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Cited by 266Biochemical and Structural CharacterizationBacterial Genetics and BiotechnologyAntimicrobial Resistance in Staphylococcus

Protein sorting to the cell wall envelope of Gram-positive bacteria

Open access
Ton-That, Hung, Marraffini, Luciano A., Schneewind, Olaf·2004·Biochimica et Biophysica Acta (BBA) - Molecular Cell Research
DOI 10.1016/j.bbamcr.2004.04.014
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Abstract

The covalent anchoring of surface proteins to the cell wall envelope of Gram-positive bacteria occurs by a universal mechanism requiring sortases, extracellular transpeptidases that are positioned in the plasma membrane. Surface protein precursors are first initiated into the secretory pathway of Gram-positive bacteria via N-terminal signal peptides. C-terminal sorting signals of surface proteins, bearing an LPXTG motif or other recognition sequences, provide for sortase-mediated cleavage and acyl enzyme formation, a thioester linkage between the active site cysteine residue of sortase and the C-terminal carboxyl group of cleaved surface proteins. During cell wall anchoring, sortase acyl enzymes are resolved by the nucleophilic attack of peptidoglycan substrates, resulting in amide bond formation between the C-terminal end of surface proteins and peptidoglycan cross-bridges within the bacterial cell wall envelope. The genomes of Gram-positive bacteria encode multiple sortase genes. Recent evidence suggests that sortase enzymes catalyze protein anchoring reactions of multiple different substrate classes with different sorting signal motif sequences, protein linkage to unique cell wall anchor structures as well as protein polymerization leading to the formation of pili on the surface of Gram-positive bacteria.

AI snapshot

Written from the paper’s full text.

TL;DR

This review describes how Gram-positive bacteria covalently attach surface proteins and pili to the peptidoglycan envelope using sortase transpeptidases. It synthesizes evidence that sortases recognize C-terminal sorting signals, form acyl-enzyme intermediates, and link substrates to cell wall precursors or other pilin subunits.

Key findings

  • Sortase-mediated anchoring depends on N-terminal secretion signals and C-terminal sorting signals; the canonical signal includes an LPXTG motif, a hydrophobic region, and a positively charged tail. Sortase cleaves between threonine and glycine, forms a thioester acyl enzyme, and resolves it via nucleophilic attack from a peptidoglycan cross-bridge or lipid II, producing an amide bond.
  • *Staphylococcus aureus* sortase A is a class I enzyme of 206 amino acids with an eight-stranded β-barrel and a catalytic Cys-His pair; histidine 120 is required for catalysis. Sortase B instead cleaves an NPQTN signal in IsdC. *S. aureus* strains carry genes for 18–22 LPXTG surface proteins, and deleting *srtA* blocks their anchoring and reduces virulence in animal models.
  • Multiple sortases and non-LPXTG signals exist. *Streptococcus pyogenes* has four sortase genes; deleting *srtA* blocks anchoring of M6, protein F, ScpA, and GRAB, but not T6, while deleting *srtB* blocks T6. *Listeria monocytogenes* SrtB anchors SvpA via an NAKTN motif.
  • Sortases also polymerize pili. In *Corynebacterium diphtheriae*, SpaA forms the pilus shaft, SpaB appears at intervals, and SpaC is at the tip; deleting *srtA* abolishes pilus assembly, and substitutions in a conserved pilin-motif lysine or the LPXTG motif prevent assembly.

Methods

  • Narrative review, not primary research; it synthesizes published genetic, biochemical, structural, and microscopy studies on Gram-positive surface protein sorting and sortase enzymes.
  • Data/sample: cited literature and genome analyses across species including *S. aureus*, *L. monocytogenes*, *S. pyogenes*, *C. diphtheriae*, *Actinomyces naeslundii*, and *Streptomyces coelicolor*; no new experimental sample or dataset is reported.
  • Main analysis: conceptual synthesis of sorting-signal recognition, sortase catalysis, cell wall anchoring, pilus assembly, iron acquisition, and chaplin-mediated hyphae formation.

Limitations

  • The paper does not explicitly list formal limitations; it identifies unresolved questions, including how two sortases distinguish substrates carrying the same LPXTG motif, the role of the NAKTN sequence in SvpA anchoring, the function of listerial SrtB, and the mechanism of streptococcal fimbrial polymerization.
  • Evident from the text: as a review, it presents no new experimental data and does not describe a systematic search strategy or inclusion criteria; several models are proposed as hypotheses rather than demonstrated mechanisms.

Model-written summary. Check it against the paper before relying on it.

Integrity signals

Registry

Crossref · 10.1016/j.bbamcr.2004.04.014

Cites

70 of 70 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

86 of 178 cited sources checked · 43 supported · 1 flagged · accuracy not yet measured

  • Premisecitation

    Two groups identified a set of six genes encoding proteins likely involved in aerial hyphae formation, named chaplins.

    “Recently, two groups have identified a set of six genes encoding proteins that are likely involved in aerial hyphae formation and which were named chaplins [66,67].”
    Quote in the paperNot a substantial claim2 of 2 sources checked
    • cites [66] Claessen, 2003, Genes Dev source

      The ‘Identification and characterization of the chaplins of S. coelicolor’ section (page not provided) says the authors identified eight homologous genes and named them chaplins, not six. The ‘Chaplins are involved in formation of aerial hyphae’ section supports their role in aerial hyphae formation; it describes deletion of up to six genes, which does not make the identified set six genes. (LLM, conf=0.90)

      Experimental — accuracy not yet measured
    • cites [67] Elliot, 2003, Genes Dev source

      The Identification section names the chaplin genes chpA–H, and the A model of chaplin assembly and function section explicitly says the family has eight members, not six. The paper does support their involvement in aerial mycelium formation and refers to an accompanying manuscript by another group. (LLM, conf=0.89)

      Checked by a reasoning model — may be wrong.

      Experimental — accuracy not yet measured
  • Premisecitation

    Surface protein precursors are first initiated into the secretory pathway of Gram-positive bacteria via N-terminal signal peptides.

    “Surface protein precursors are first initiated into the secretory pathway of Gram-positive bacteria via N-terminal signal peptides.”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [31] Bae, 2003, J. Bacteriol source
  • Premisereasoning

    During cell wall anchoring, sortase acyl enzymes are resolved by the nucleophilic attack of peptidoglycan substrates, resulting in amide bond formation between the C-terminal end of surface proteins and peptidoglycan cross-bridges within the bacterial cell wall envelope.

    “During cell wall anchoring, sortase acyl enzymes are resolved by the nucleophilic attack of peptidoglycan substrates, resulting in amide bond formation between the C-terminal end of surface proteins and peptidoglycan cross-bridges within the bacterial cell wall envelope.”
    Quote in the paperSubstantial claim3 of 5 sources checked
    • cites [28] Ruzin, 2002, J. Bacteriol source

      Split into 2 atoms — 1 confirmed, 1 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured
    • cites [29] Perry, 2002, J. Biol. Chem source
    • cites [30] Ton-That, 1999, J. Biol. Chem source
    • cites [32] Ton-That, 1997, J. Biol. Chem source
    • cites [51] Ton-That, 1999, Proc. Natl. Acad. Sci. U. S. A source

      Split into 2 atoms — 1 confirmed, 1 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured
  • Premisecitation

    The genomes of Gram-positive bacteria encode multiple sortase genes.

    “The genomes of Gram-positive bacteria encode multiple sortase genes.”
    • Also stated in: § 4. Sortase · plain
      “Sortase homologs have been found in all available Gram-positive bacterial genomes and in most cases, more than one sortase gene has been identified [36,37].”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [36] Comfort, 2004, Infect. Immun source
    • cites [37] Pallen, 2001, Trends Microbiol source
  • Premisecitation

    Peptidoglycan biosynthesis occurs in the bacterial cytoplasm, membrane and extracellular cell wall compartments.

    “Peptidoglycan biosynthesis occurs in the bacterial cytoplasm, membrane and extracellular cell wall compartments [5,27].”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [5] Navarre, 1999, Microbiol. Mol. Biol. Rev source
    • cites [27] Strominger, 1967, Fed. Proc

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims. 36
  • Classified as probably not a substantial claim. 19

  • May combine two claims.

    Premisecitation

    C-terminal sorting signals of surface proteins, bearing an LPXTG motif or other recognition sequences, provide for sortase-mediated cleavage and acyl enzyme formation, a thioester linkage between the active site cysteine residue of sortase and the C-terminal carboxyl group of cleaved surface proteins.

    “C-terminal sorting signals of surface proteins, bearing an LPXTG motif or other recognition sequences, provide for sortase-mediated cleavage and acyl enzyme formation, a thioester linkage between the active site cysteine residue of sortase and the C-terminal carboxyl group of cleaved surface proteins.”
    Quote in the paperSubstantial claim2 of 3 sources checked
    • cites [34] Navarre, 1994, Mol. Microbiol source
    • cites [51] Ton-That, 1999, Proc. Natl. Acad. Sci. U. S. A source

      Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured
    • cites [52] Ton-That, 2000, J. Biol. Chem source

      Split into 2 atoms — 0 confirmed, 2 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Although bacterial peptidoglycan structure varies from one species to another, several structural or functional elements are conserved.

    “Although bacterial peptidoglycan structure varies from one species to another, several structural or functional elements are conserved (Fig. 1) [15,22].”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [15] Schleifer, 1972, Bacteriol. Rev source
    • cites [22] Ghuysen, 1968, Bacteriol. Rev source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Glycan chains are cross-linked by short cell wall peptides, generating a three-dimensional molecular network that maintains the integrity of the bacterium.

    “Glycan chains are cross-linked by short cell wall peptides, generating a three-dimensional molecular network that maintains the integrity of the bacterium [24,25].”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [24] Ghuysen, 1965, Biochemistry source

      The indexed copy identifies the 1965 paper in a bibliographic entry (Biochemistry 4, pp. 2245–2254), but the retrieved passages do not contain its substantive text. Searches for peptide cross-links and a three-dimensional glycan network returned material about other works, so this copy cannot verify what the cited paper says about the claimed structure or its role in bacterial integrity. (LLM, conf=0.76)

      Experimental — accuracy not yet measured
    • cites [25] Tipper, 1965, Proc. Natl. Acad. Sci. U. S. A source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Reassociation of anchorless adhesins and invasins occurs in Streptococcus pyogenes.

    “(vi) Reassociation of anchorless adhesins and invasins (in Streptococcus pyogenes) [14].”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [14] Pancholi, 1997, J. Exp. Med source

      The Abstract describes surface dehydrogenase (SDH) on group A streptococci, and the Results section on streptococcal adherence and invasion examines their interaction with pharyngeal cells; page numbers are not available in our copy. Neither passage establishes that anchorless adhesins or invasins leave and reassociate with the bacterial surface. Searches for reassociation, anchoring, and rebinding found no passage addressing that process. (LLM, conf=0.74)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    While most sorting signals carry the LPXTG motif, in many other cases they harbor variations of the sequence motif.

    “While most of these sorting signals carry the LPXTG motif, in many other cases they harbor variations of the sequence motif.”
    Quote in the paperNot a substantial claim3 of 4 sources checked
    • cites [5] Navarre, 1999, Microbiol. Mol. Biol. Rev source

      The passage preceding Table 1 (section labeled Abstract; page unavailable) says the LPXTG motif is conserved in all known wall-anchored surface proteins, while noting substitutions at the threonine position. This supports the existence of variants, but not the claim that many sorting signals carry variations rather than the LPXTG motif. (LLM, conf=0.85)

      Experimental — accuracy not yet measured
    • cites [35] Mazmanian, 2002, Proc. Natl. Acad. Sci. U. S. A source

      Table 2 lists predominantly LPXTG sorting signals, alongside LPAAG and LPKAG signals. The Results and Discussion also identify an NPQTN signal anchored by SrtB. These passages support the existence of variations, but do not establish that they occur in “many other cases” beyond the signals examined here. (LLM, conf=0.78)

      Experimental — accuracy not yet measured
    • cites [36] Comfort, 2004, Infect. Immun source
    • cites [37] Pallen, 2001, Trends Microbiol source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Based on the presence or absence of topogenic sequences, sortases can be divided into two classes.

    “Based on the presence or absence of topogenic sequences, sortases can be divided into two classes.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [41] Mazmanian, 2001, Mol. Microbiol source

      The “A second sortase gene (srtB)” section says that S. aureus has two sortase genes, srtA and srtB, and suggests their enzymes may act on different substrates. It does not classify sortases generally into two classes based on the presence or absence of topogenic sequences; no page number is available in our copy. (LLM, conf=0.76)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    Deletion of the srtA gene abolishes the function of all of these sorting signals and abrogates anchoring and display of an entire class of surface proteins.

    “Deletion of the srtA gene abolishes the function of all of these sorting signals and abrogates anchoring and display of an entire class of surface proteins [35,39].”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites [35] Mazmanian, 2002, Proc. Natl. Acad. Sci. U. S. A source
    • cites [39] Mazmanian, 1999, Science source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The major class of sortases encompasses enzymes with an N-terminal signal peptide/membrane anchor (class I).

    “The major class of sortases encompasses enzymes with an N-terminal signal peptide/ membrane anchor (class I).”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [41] Mazmanian, 2001, Mol. Microbiol source

      The Sortase (SrtA) section describes SrtA as having a putative N-terminal membrane-spanning domain. Our copy does not classify sortases as “class I” or say that this is the major class; its references to signal peptides concern the surface-protein substrates, not sortase enzymes. No page number is available in our copy. (LLM, conf=0.86)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    SvpA encompasses an NAKTN cell wall sorting motif and its structural gene is transcribed together with the srtB gene in the same operon.

    “SvpA encompasses an NAKTN cell wall sorting motif and its structural gene is transcribed together with the srtB gene in the same operon.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [38] Bierne, 2004, J. Bacteriol source

      The Results identify an NAKTN motif in SvpA and report RT-PCR evidence suggesting that svpA and srtB belong to the same seven-gene transcriptional unit. The paper describes NAKTN only as a possible sorting-recognition motif, however; it does not establish that the motif itself performs that function. (LLM, conf=0.84)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    Inactivation of the streptococcal srtB gene abolished the surface display and anchoring of T6 protein without affecting that of M6 protein, protein F, C5a peptidase (ScpA), or GRAB.

    “However, inactivation of the streptococcal srtB gene abolished the surface display and anchoring of T6 protein without affecting that of M6 protein, protein F, C5a peptidase (ScpA), or GRAB [50].”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [50] Barnett, 2002, J. Bacteriol source

      The Results report that the srtB mutant had reduced T6 on the cell surface, while M6, protein F, ScpA, and GRAB were unaffected. The claim's protein-specific distinction is supported, but “abolished” overstates the reported reduction. (LLM, conf=0.90)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    Sortase B mutant listeria do not display SvpA on the bacterial surface, a phenotype that could be complemented by the expression of plasmid-encoded srtB.

    “Sortase B mutant listeria do not display SvpA on the bacterial surface, a phenotype that could be complemented by the expression of plasmid-encoded srtB [38].”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [38] Bierne, 2004, J. Bacteriol source

  • May combine two claims.

    Premisecitation

    Sortase cleaves the LPXTG motif between the threonine (T) and the glycine (G) residues both in vivo and in vitro, capturing cleaved polypeptide as a thioester-linked acyl enzyme at its active site cysteine residue.

    “Sortase cleaves the LPXTG motif between the threonine (T) and the glycine (G) residues both in vivo and in vitro, capturing cleaved polypeptide as a thioester-linked acyl enzyme at its active site cysteine residue [34,51,52].”
    Quote in the paperSubstantial claim2 of 3 sources checked
    • cites [34] Navarre, 1994, Mol. Microbiol source
    • cites [51] Ton-That, 1999, Proc. Natl. Acad. Sci. U. S. A source

      The Discussion states that sortase cleaves between threonine and glycine in the LPXTG motif, and the Results show cleavage by purified sortase in vitro. The paper presents capture of the cleaved polypeptide as a thioester linked to the enzyme’s cysteine as a proposed mechanism supported by hydroxylamine and cysteine-184 experiments, rather than as an established observation in both settings. (LLM, conf=0.84)

      Experimental — accuracy not yet measured
    • cites [52] Ton-That, 2000, J. Biol. Chem source

      The in vitro cleavage results identify the bond between threonine and glycine, and the introduction describes sortase-dependent cleavage of LPXTG sorting signals in staphylococci. However, the paper presents capture of the cleaved protein as a cysteine-linked thioester intermediate as a proposed mechanism, not an observed result; it does not directly establish the precise in vivo cleavage bond. Section labels are available in our copy, but page numbers are not. (LLM, conf=0.88)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    Staphylococcal srtA is constitutively expressed, whereas srtB expression is only induced under iron starvation, a condition that bacteria encounter when entering their mammalian hosts.

    “Staphylococcal srtA is constitutively expressed, whereas srtB expression is only induced under iron starvation, a condition that bacteria encounter when entering their mammalian hosts [35,49].”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [35] Mazmanian, 2002, Proc. Natl. Acad. Sci. U. S. A source
    • cites [49] Mazmanian, 2003, Science source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The second, minor class is formed by sortases with an N-terminal signal peptide and a C-terminal membrane anchor (class II).

    “The second, minor class is formed by sortases with an N-terminal signal peptide and a C-terminal membrane anchor (class II) [41].”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [41] Mazmanian, 2001, Mol. Microbiol source

      The “A second sortase gene (srtB)” section identifies a second sortase gene in S. aureus, but does not classify sortases by membrane topology. Searches for “class II,” “minor class,” and a sortase with an N-terminal signal peptide and C-terminal membrane anchor found no passage stating the claimed classification; the paper instead describes an N-terminal membrane anchor for SrtA. (LLM, conf=0.76)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    S. parasanguis assembles adhesive filaments containing Fap1, which harbors a cell wall sorting signal.

    “S. parasanguis assembles adhesive filaments containing Fap1, which harbors a cell wall sorting signal.”
    Quote in the paperNot a substantial claim1 of 1 sources checked
    • cites [3] Wu, 2001, Crit. Rev. Oral Biol. Med source

  • May combine two claims.

    Premisecitation

    Orf4 is responsible for assembly of type I pili but not type II fimbriae, whereas Orf365 fulfills the reciprocal role for type II fimbriae.

    “Orf4 appears to be responsible for the assembly of type I pili but not of type II fimbriae, whereas Orf365 fulfills the reciprocal role for type II fimbriae [3,58].”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [3] Wu, 2001, Crit. Rev. Oral Biol. Med source

      The discussion of A. naeslundii fimbriae (p. 107) identifies Orf4 among genes involved in type I assembly and Orf365 as a type II assembly gene. It does not establish that their roles are exclusive: it suggests some fimbrial genes may be interchangeable and that Orf365 may also process a type I subunit. (LLM, conf=0.88)

      Experimental — accuracy not yet measured
    • cites [58] Yeung, 1999, Crit. Rev. Oral Biol. Med source

  • May combine two claims.

    Premisecitation

    Thioester-linked acyl-enzyme intermediates of sortase are sensitive to hydroxylaminolysis, releasing surface protein threonine hydroxamate into the extracellular medium and preventing cell wall anchoring.

    “Thioester-linked acylenzyme intermediates of sortase are sensitive to hydroxylaminolysis, releasing surface protein threonine hydroxamate into the extracellular medium and preventing cell wall anchoring [51].”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [51] Ton-That, 1999, Proc. Natl. Acad. Sci. U. S. A source

  • May combine two claims.

    Premisecitation

    Methylmethane thiosulfonate forms a disulfide bond with the sulfhydryl group of the active site cysteine, thus generating an acyl enzyme intermediate.

    “The latter reagent forms a disulfide bond with the sulfhydryl group of the active site cysteine, thus generating an acyl enzyme intermediate.”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [30] Ton-That, 1999, J. Biol. Chem source
    • cites [51] Ton-That, 1999, Proc. Natl. Acad. Sci. U. S. A source

      The Results state that methanethiosulfonate forms a disulfide with sulfhydryl groups and inactivates sortase. But the Discussion describes the acyl-enzyme intermediate as a thioester formed when sortase cleaves an LPXTG-bearing protein, not as a product of the reagent’s disulfide bond. (LLM, conf=0.88)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    Disruption of orf4 caused FimP and Orf1 subunits to accumulate in the envelope and prevented fimbrial structure assembly.

    “A similar result was observed when orf4 was disrupted; FimP and Orf1 subunits accumulated in the envelope, and the fimbrial structure was not assembled [59].”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [59] Yeung, 1997, Infect. Immun source

      In “Potential role of the putative ORFs in fimbria synthesis and function” (page not provided), the ORF4-disrupted mutant expressed the 65-kDa fimbrial structural subunit; the Discussion reports that it lacked assembled fimbriae. The paper does not report accumulation of FimP or Orf1 in the envelope, and says that only the 65-kDa subunit was detected in this mutant. (LLM, conf=0.88)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    Chaplins D-H are very short polypeptides, whereas chaplins A-C are longer and carry a C-terminal sorting signal (LAXTG motif).

    “Chaplins D -H are very short polypeptides, whereas chaplins A -C are longer and carry a C-terminal sorting signal (LAXTG motif).”
    Quote in the paperNot a substantial claim2 of 2 sources checked
    • cites [66] Claessen, 2003, Genes Dev source
    • cites [67] Elliot, 2003, Genes Dev source

  • May combine two claims.

    Premisecitation

    Deletion of six chaplin genes (chpA-H) hindered the formation of aerial hyphae; the defect could be complemented by the addition of exogenous chaplin proteins.

    “Deletion of six chaplin genes (chpA -H) hindered the formation of aerial hyphae; the defect could be complemented by the addition of exogenous chaplin proteins.”
    Quote in the paperSubstantial claim2 of 2 sources checked
    • cites [66] Claessen, 2003, Genes Dev source
    • cites [67] Elliot, 2003, Genes Dev source

      Split into 2 atoms — 1 confirmed, 1 partially supported, 0 disputed, 0 misattributed, 0 unverifiable. Expand the claim to see per-atom verdicts.

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    IsdB and IsdA carry LPXTG motif sorting signals and are cell wall anchored by sortase A.

    “Two other surface proteins, encoded by isdB and isdA, carry LPXTG motif sorting signals and are cell wallanchored by sortase A.”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [35] Mazmanian, 2002, Proc. Natl. Acad. Sci. U. S. A source
    • cites [49] Mazmanian, 2003, Science source

  • May combine two claims.

    Premisecitation

    IsdC is synthesized as a precursor with a NPQTN type C-terminal sorting signal that is cleaved and tethered to the cell wall envelope via a sortase B-dependent mechanism.

    “One of these binding proteins, IsdC, is synthesized as a precursor with a NPQTN type C-terminal sorting signal that is cleaved and tethered to the cell wall envelope via a sortase B-dependent mechanism.”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites [35] Mazmanian, 2002, Proc. Natl. Acad. Sci. U. S. A source
    • cites [49] Mazmanian, 2003, Science source

  • May combine two claims.

    Premisecitation

    Heme-iron is transported across the cell wall envelope (IsdA, IsdC) and plasma membrane (IsdD, IsdE and IsdF).

    “Heme-iron is then transported across the cell wall envelope (IsdA, IsdC) and plasma membrane (IsdD, IsdE and IsdF).”
    Quote in the paperSubstantial claim1 of 2 sources checked
    • cites [35] Mazmanian, 2002, Proc. Natl. Acad. Sci. U. S. A source

      The isd operon section and Fig. 1 identify IsdE and IsdF as a putative iron transporter, while the IsdC cell-wall-anchoring results (Fig. 3) establish that IsdC is attached to the cell wall. These passages do not establish heme-iron transport across either barrier or the claimed transport roles of IsdA and IsdD. Page numbers are not available in our copy. (LLM, conf=0.87)

      Experimental — accuracy not yet measured
    • cites [49] Mazmanian, 2003, Science source

  • May combine two claims.

    Interpretationcitation

    Chaplins A-C are anchored to the peptidoglycan via sorting signals with a LAXTG motif, allowing the smaller chaplins D-H to be immobilized and nucleated on the cell surface by interaction with their chaplin domains.

    “It is suggested that chaplins A -C are anchored to the peptidoglycan via sorting signals with a LAXTG motif, allowing the smaller chaplins DH to be immobilized and nucleated on the cell surface by interaction with their chaplin domains (Fig. 7) [66].”
    Quote in the paperSubstantial claim1 of 1 sources checked
    • cites [66] Claessen, 2003, Genes Dev source

      The Discussion (page unavailable) proposes that ChpA-C may be linked to peptidoglycan through their LAXTG motifs and coassemble with ChpD-H through homologous sequences, thereby immobilizing the smaller chaplins at the cell surface. It does not say that ChpA-C nucleate ChpD-H assembly; that additional mechanism is unsupported. (LLM, conf=0.84)

      Experimental — accuracy not yet measured

  • May combine two claims.

    Premisecitation

    IsdB binds hemoglobin and IsdA and IsdB presumably remove bound heme-iron.

    “These factors first bind hemoglobin (IsdB) and presumably remove bound heme-iron (IsdA, IsdB).”
    Quote in the paperNot a substantial claim1 of 2 sources checked
    • cites [35] Mazmanian, 2002, Proc. Natl. Acad. Sci. U. S. A source

      The unpaginated “srtB and the isd Operon” passage describes a putative iron-acquisition system, and the IsdC passages address cell-wall anchoring. Searches for IsdA, IsdB, hemoglobin, and heme-iron removal found no passage in our copy saying that IsdB binds hemoglobin or that IsdA and IsdB remove its bound heme-iron. (LLM, conf=0.76)

      Experimental — accuracy not yet measured
    • cites [49] Mazmanian, 2003, Science source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Gram-positive bacteria are surrounded by a rigid cell wall, also referred to as murein or peptidoglycan.

    “Gram-positive bacteria are surrounded by a rigid cell wall, also referred to as ''murein'' or ''peptidoglycan'' [15].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [15] Schleifer, 1972, Bacteriol. Rev source

  • May combine two claims.

    Interpretationnone given

    Recent evidence suggests that sortase enzymes catalyze protein anchoring reactions of multiple different substrate classes with different sorting signal motif sequences, protein linkage to unique cell wall anchor structures, and protein polymerization leading to the formation of pili on the surface of Gram-positive bacteria.

    “Recent evidence suggests that sortase enzymes catalyze protein anchoring reactions of multiple different substrate classes with different sorting signal motif sequences, protein linkage to unique cell wall anchor structures as well as protein polymerization leading to the formation of pili on the surface of Gram-positive bacteria.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Some bacterial adhesins that interact with extracellular matrix molecules of their host have been classified as microbial surface components recognizing adhesive matrix molecules (MSCRAMMs).

    “Some bacterial adhesins, for example surface proteins that interact with extracellular matrix molecules of their host (fibronectin, collagen, laminin, fibrinogen or others), have been classified as microbial surface components recognizing adhesive matrix molecules (MSCRAMMs); full reviews of MSCRAMMs have been published elsewhere [4].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [4] Patti, 1994, Annu. Rev. Microbiol source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Insertion of surface proteins into the plasma membrane via an alpha-helical membrane anchor structure occurs for ActA of L. monocytogenes.

    “(iv) Insertion of surface proteins into the plasma membrane via an alpha-helical membrane anchor structure (ActA of L. monocytogenes) [11].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [11] Kocks, 1992, Cell source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The amino group of the first amino acid in the peptide moiety is linked to the carboxyl group of the lactic acid of N-acetylmuramic acid via an amide bond.

    “The amino group of the first amino acid in the peptide moiety is linked to the carboxyl group of the lactic acid of N-acetylmuramic acid via an amide bond (Fig. 1) [26].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [26] Tipper, 1965, Biochemistry source

  • May combine two claims.

    Premisecitation

    After synthesis in the cytoplasm, nucleotide precursors form a phosphodiester bond with an undecaprenol carrier (lipid I) and then N-acetylglucosamine is attached to generate lipid II.

    “After synthesis in the cytoplasm, nucleotide precursors form a phosophodiester bond with an undecaprenol carrier (lipid I) and then N-acetylglucosamine is attached to generate lipid II [27].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [27] Strominger, 1967, Fed. Proc

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    The glycan strands of all bacterial peptidoglycan consist of repeat disaccharide units, N-acetylglucosamine-(β1-4)-N-acetylmuramic acid (GlcNAc-MurNAc).

    “The glycan strands of all bacterial peptidoglycan consist of repeat disaccharide units, N-acetylglucosamine -(h1-4)-N-acetylmuramic acid (GlcNAc -MurNAc) [23].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [23] Ghuysen, 1963, Biochemistry source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Six different mechanisms of protein anchoring to the Gram-positive bacterial envelope are currently known.

    “Six different mechanisms of protein anchoring to the Gram-positive bacterial envelope are currently known [6,7].”
    Quote in the paperNot a substantial claim0 of 2 sources checked
    • cites [6] Cossart, 2000, Proc. Natl. Acad. Sci. U. S. A source
    • cites [7] Chhatwal, 2002, Trends Microbiol source

  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisecitation

    Staphylococcal sortase A, a class I enzyme, contains 206 amino acid residues.

    “Staphylococcal sortase A, a class I enzyme, contains 206 amino acid residues [42].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [42] Ilangovan, 2001, Proc. Natl. Acad. Sci. U. S. A source

  • May combine two claims.

    Premisecitation

    The fimP and fimA genes encode major protein subunits of A. naeslundii type I and type II fimbriae, respectively.

    “Yeung [58] showed that the fimP and fimA genes encode major protein subunits of A. naeslundii type I and type II fimbriae, respectively.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [58] Yeung, 1999, Crit. Rev. Oral Biol. Med source

  • May combine two claims.

    Premisecitation

    Actinomyces naeslundii forms fimbriae, short filaments on the bacterial surface that are composed of FimP (type I fimbriae) or FimA (type II fimbriae).

    “Actinomyces naeslundii, a human pathogen that can be isolated from supragingival dental plaque, forms fimbriae, short filaments on the bacterial surface that are composed of FimP (type I fimbriae) or FimA (type II fimbriae) [58].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [58] Yeung, 1999, Crit. Rev. Oral Biol. Med source

  • May combine two claims.

    Premisecitation

    Assembled corynebacterial pili are released from the bacterial surface by treatment with murein hydrolase, suggesting that pilus fibers may be anchored to the cell wall envelope.

    “Assembled pili are released from the bacterial surface by treatment with murein hydrolase, suggesting that pilus fibers may be anchored to the cell wall envelope.”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [62] Ton-That, 2003, Mol. Microbiol source

  • May combine two claims.

    Premisecitation

    The fimA gene is located elsewhere on the actinomycetal chromosome and the orf365 gene is located immediately adjacent to fimA.

    “The fimA gene is located elsewhere on the actinomycetal chromosome and the orf365 gene is located immediately adjacent to fimA [60].”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [60] Yeung, 1998, J. Bacteriol

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • May combine two claims.

    Interpretationreasoning

    Corynebacterial pili are composed of covalently linked protein subunits and tethered to the bacterial cell wall.

    “arguments support the hypothesis that corynebacterial pili are composed of covalently linked protein subunits and tethered to the bacterial cell wall.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [62] Ton-That, 2003, Mol. Microbiol source

  • May combine two claims.

    Interpretationreasoning

    Actinomyces sortases appear to polymerize fimbrial precursors into a supramolecular structure that may be composed of repeating subunits, in contrast to staphylococcal sortases that anchor monomeric surface proteins to the cell wall envelope.

    “In contrast to staphylococci, where sortase anchors monomeric surface proteins to the cell wall envelope, Actinomyces sortases appear to polymerize fimbrial precursors into a supramolecular structure that may be composed of repeating subunits.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Proteinaceous filaments on microbial surfaces, named pili or fimbriae, provide adhesive functions and play important roles during the establishment of respiratory, urinary, periodontal and intestinal infectious diseases.

    “Proteinaceous filaments on microbial surfaces, named pili or fimbriae, provide adhesive functions and play important roles during the establishment of respiratory, urinary, periodontal and intestinal infectious diseases [54 -57].”
    Quote in the paperNot a substantial claim0 of 4 sources checked
    • cites [54] Pichichero, 1982, Lancet source
    • cites [55] Hultgren, 1993, Cell source
    • cites [56] Thelin, 1996, Infect. Immun source
    • cites [57] Yeung, 2000

      Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  • Classified as probably not a substantial claim. May combine two claims.

    Interpretationreasoning

    The polymerization of Actinomyces fimbrial precursors is thought to require formation of novel sortase-mediated peptide bonds, with the cleaved sorting signal presumably attached to another fimbrial subunit.

    “Such a scenario is thought to require the formation of novel sortase-mediated peptide bonds, as the cleaved sorting signal is presumably attached to another fimbrial subunit (vide infra).”
    Quote in the paperSubstantial claim

  • May combine two claims.

    Premisecitation

    SpaA is distributed uniformly along the pilus shaft, SpaB is observed at regular intervals, and SpaC seems positioned at the pilus tip.

    “SpaA, the major pilin protein, is distributed uniformly along the pilus shaft, while SpaB is observed at regular intervals and SpaC seems positioned at the pilus tip (Fig. 4B -E).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites [62] Ton-That, 2003, Mol. Microbiol source

  • May combine two claims.

    Premisecitation

    Substitution of the conserved lysine with alanine or arginine abolished pilus assembly, as did amino acid substitutions within the LPXTG motif.

    “Substitution of this lysine with alanine or arginine abolished pilus assembly, as did amino acid substitutions within the LPXTG motif.”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [62] Ton-That, 2003, Mol. Microbiol source

  • Probably not a substantial claim: may not pass S3 (load-bearing), S4 (based). May combine two claims.

    Interpretationreasoning

    ChpE and ChpH are expressed during mycelium formation and are presumed to form a film that reduces water surface tension and allows hyphal protrusion into the air.

    “As ChpE and ChpH are expressed during mycelium formation, these proteins are presumed to form a film that reduces water surface tension and allows hyphal protrusion into the air.”
    Quote in the paperNot a substantial claim

  • Classified as probably not a substantial claim.

    Interpretationreasoning

    Iron acquisition strategies of L. monocytogenes, which assumes a predominantly intracellular life cycle, seem to differ markedly from the mechanisms used by the extracellular pathogen S. aureus.

    “Further investigation will be required to address the function of listerial sortase B, as iron acquisition strategies of L. monocytogenes, which assumes a predominantly intracellular life cycle, seem to differ markedly from the mechanisms used by the extracellular pathogen S. aureus.”
    Quote in the paperSubstantial claim

  • Probably not a substantial claim: may not pass S4 (based).

    Premisenone given

    Sortases are membrane transpeptidases that catalyze amide bond exchange mechanisms, using sorting signals of precursor proteins and cell wall envelope components as substrates.

    “Sortases are membrane transpeptidases that catalyze amide bond exchange mechanisms, using sorting signals of precursor proteins and cell wall envelope components as substrates.”
    Quote in the paperNot a substantial claim

  • Probably not a substantial claim: may not pass S4 (based). May combine two claims.

    Interpretationnone given

    All chaplins, which are expressed in the aerial hyphae, are presumed to diffuse to the outer surface and to assemble a layer of fibrils that confers hydrophobicity to the aerial hypha.

    “All chaplins, which are expressed in the aerial hyphae, are presumed to diffuse to the outer surface and to assemble a layer of fibrils that confers hydrophobicity to the aerial hypha.”
    Quote in the paperNot a substantial claim

  • May combine two claims.

    Interpretationcitation

    The LPXTG anchor structures of IsdA and IsdB promote receptor function for hemoglobin and heme-iron on the staphylococcal surface, whereas the NPQTN structure may function in heme-iron passage across the bacterial cell wall.

    “The LPXTG anchor structures of IsdA and IsdB promote receptor function for hemoglobin and heme-iron on the staphylococcal surface, whereas the NPQTN structure may function in heme-iron passage across the bacterial cell wall (Fig. 6).”
    Quote in the paperSubstantial claim0 of 1 sources checked
    • cites [49] Mazmanian, 2003, Science source

  • May combine two claims.

    Premisenone given

    Sortases are strategically positioned on the outside of bacterial cells and catalyze amide bond exchange reactions with newly translocated polypeptides, reactions that are fueled by peptide bond cleavage without direct consumption of high energy phosphates.

    “Sortases are strategically positioned on the outside of bacterial cells and catalyze amide bond exchange reactions with newly translocated polypeptides, reactions that are fueled by peptide bond cleavage without direct consumption of high energy phosphates.”
    Quote in the paperNot a substantial claim
51 of 51

  • The authors state this as an assumption.

    The hydrophobic and positively charged residues of the cell wall sorting signal retain the translocated protein within the plasma membrane until the substrate is recognized by sortase.

    “It is presumed that the hydrophobic and positively charged residues of the cell wall sorting signal retain the translocated protein within the plasma membrane until the substrate is recognized by sortase [8] (Fig. 3).”

  • The authors state this as an assumption.

    If a surface protein gene is located in the same transcriptional unit with a sortase gene, the two genes encode enzyme/substrate pairs.

    “If a surface protein gene is located in the same transcriptional unit with a sortase gene, it is generally presumed that the two genes encode enzyme/substrate pairs [37].”

  • The authors state this as an assumption.

    SrtB-mediated anchoring can provide for a designated anchor structure, subcellular location and/or function of IsdC in heme-iron transport.

    “It is presumed that SrtB-mediated anchoring can provide for a designated anchor structure, subcellular location and/or function of IsdC in heme-iron transport.”
3 of 3

Self-check

Percentages, sums and reported differences re-computed from the paper’s own numbers.

Each contradiction between two passages listed here was confirmed by an independent check.

  • A disulfide modification is called an acyl-enzyme intermediate

    Minor

    The paper defines the sortase acyl-enzyme intermediate as a thioester linking sortase to a cleaved surface protein. It later calls a disulfide formed by an inhibitory reagent an acyl-enzyme intermediate, although that is a different linkage.

  • Chaplin count conflicts with the named groups

    Minor

    The text says there are six chaplin genes, but its two named groups, A-C and D-H, cover eight distinct chaplins.

2 of 2

Cites

Flagged first, then by citations

Research works printed but not linked: 3

  1. Strominger, 1967, Fed. Proc, 26, 9
  2. Yeung, 1998, J. Bacteriol, 66, 1482
  3. Fouet, 2002, Curr. Top. Microbiol. Immunol, 271, 87

Cited by

Sorted by citations

Related

Authors
Ton-That, H., Marraffini, L. A., & Schneewind, O.
Affiliations
University of Chicago (US)
Corresponding author
Schneewind, Olaf
ORCID
Venue
Biochimica et Biophysica Acta (BBA) - Molecular Cell Research
Publisher
Elsevier BV
Published
2004-11
Volume
1694
Issue
1-3
Pages
269-278
ISSN
0167-4889 (ISSN-L)
DOI
10.1016/j.bbamcr.2004.04.014
OpenAlex
W2150931072
Semantic Scholar
d33cf365f4b1b017bb3637036e6706584b88d67e
Cited by
266
References
69
Citations by year
2026: 1 · 2025: 5 · 2024: 3 · 2023: 7 · 2022: 5 · 2021: 7 · 2020: 8 · 2019: 5 · 2018: 6 · 2017: 12 · 2016: 14 · 2015: 12 · 2014: 20 · 2013: 18 · 2012: 19
FWCI
1.39
Type
journal article
Language
en
Open access
Licence
Locations
  • Biochimica et Biophysica Acta (BBA) - Molecular Cell Research (publishedVersion)
  • PubMed (publishedVersion)
Funders
  • U.S. Public Health Service
  • National Institute of Allergy and Infectious Diseases (AI38897, AI52474, R01AI038897, R01AI052474)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Biochemical and Structural Characterization
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Genetics › Bacterial Genetics and Biotechnology
  • Health Sciences › Medicine › Infectious Diseases › Antimicrobial Resistance in Staphylococcus
Keywords
sortase, protein sorting, cell wall anchoring, Gram-positive bacteria, surface proteins, LPXTG motif, signal peptide, thioester linkage, peptidoglycan, acyl-enzyme, fimbriae, protein polymerization, plasma membrane enzymes
MeSH terms
Bacterial Proteins, Cell Wall, Cysteine Endopeptidases, Gram-Positive Bacteria, Fimbriae, Bacterial, Aminoacyltransferases, Protein Transport, Protein Sorting Signals, Hyphae

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-11.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-11.

Cited sources are checked by gpt-6-sol.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

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