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Cited by 26Protein Structure and DynamicsAlzheimer's disease research and treatmentsProtein Interaction Studies and Fluorescence Analysis

Biophysical analysis of progressive C-terminal truncations of human apolipoprotein E4: insights into secondary structure and unfolding properties.

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Chroni, Angeliki, Pyrpassopoulos, Serapion, Thanassoulas, Angelos, Nounesis, George, Zannis, Vassilis I., Stratikos, Efstratios·2008·Biochemistry
DOI 10.1021/bi800469rPMC PMC2692411
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Abstract

Apolipoprotein E4 (apoE4) is a risk factor for Alzheimer's disease and has been associated with a variety of neuropathological processes. ApoE4 C-terminally truncated forms have been found in brains of Alzheimer's disease patients. Structural rearrangements in apoE4 are known to be key to its physiological functions. To understand the effect of C-terminal truncations on apoE4 lipid-free structure, we produced a series of recombinant apoE4 forms with progressive C-terminal deletions between residues 166 and 299. Circular dichroism measurements show a dramatic loss in helicity upon removal of the last 40 C-terminal residues, whereas further truncations of residues 203-259 lead to recovery of helical content. Further deletion of residues 186-202 leads to a small increase in helical content. Thermal denaturation indicated that removal of residues 260-299 leads to an increase in melting temperature but truncations down to residue 186 did not further affect the melting temperature. The progressive C-terminal truncations, however, gradually increased the cooperativity of thermal unfolding. Chemical denaturation of the apoE4 forms revealed a two-step process with a clear intermediate stage that is progressively lost as the C-terminus is truncated down to residue 230. Hydrophobic fluorescent probe binding suggested that regions 260-299 and 186-202 contain hydrophobic sites, the former being solvent accessible in the wild-type molecule and the latter being accessible only upon truncation. Taken together, our results show an important but complex role of apoE4 C-terminal segments in secondary structure stability and unfolding and suggest that interactions mediated by the C-terminal segments are important for the structural integrity and conformational changes of apoE4.

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  • All three variants exhibited similar chemical denaturation curves to wild-type apoE3, with a characteristic shallow plateau near the midpoint indicative of a transition intermediate state.

    “All three variants exhibited similar shape curves as wild-type apoE3 with a characteristic shallow plateau near the midpoint of the denaturation, indicative of a transition intermediate state as described before [43].”

    From Biophysical Analysis of Apolipoprotein E3 Variants Linked with Development of Type III Hyperlipoproteinemia (2011) · cites this paper as [43]

    The Results (Chemical Unfolding of apoE4) describe a discernible intermediate in wild-type apoE4 chemical denaturation, supporting the cited interpretation of a denaturation plateau. The paper does not establish the claimed similarity of three variants to wild-type apoE3; its apoE4 deletion variants instead show an intermediate that is reduced or abolished. (LLM, conf=0.87)

    Experimental — accuracy not yet measured

  • ApoE variants with lower thermodynamic stability and changes in conformational plasticity have been shown to have altered interdomain interactions and defective physiological functions.

    “ApoE variants with lower thermodynamic stability and changes in conformational plasticity have been shown to have altered interdomain interactions and defective physiological functions (19, 24 -28).”

    From Molecular Basis for Increased Risk for Late-onset Alzheimer Disease Due to the Naturally Occurring L28P Mutation in Apolipoprotein E4 (2014) · cites this paper as [25]

    The Discussion’s “Functional Properties of apoE4 C-Terminal Truncation Mutants” section links altered unfolding behavior to impaired lipid interactions and cholesterol efflux. But it describes a correlation between structural stabilization—not lower stability—and loss of function. The paper discusses N- and C-terminal domain interactions, but does not establish that the functionally impaired truncation variants have altered interdomain interactions. Page numbers are unavailable in our copy. (LLM, conf=0.87)

    Experimental — accuracy not yet measured

  • Both apoE4[L28P] and apoE4[Δ(166-299)] display the loss of a key unfolding intermediate during chemical denaturation.

    “Furthermore, both variants display one common characteristic, namely the loss of a key unfolding intermediate during chemical denaturation (25).”

    From Molecular Basis for Increased Risk for Late-onset Alzheimer Disease Due to the Naturally Occurring L28P Mutation in Apolipoprotein E4 (2014) · cites this paper as [25]

    The Results section (‘Chemical Unfolding of apoE4’; page not provided) reports that the chemical-denaturation intermediate is essentially absent in apoE4[Δ166–299]. The paper examines C-terminal deletion variants, but our copy does not report this finding for apoE4[L28P], so it supports only one of the two variants named. (LLM, conf=0.89)

    Experimental — accuracy not yet measured

  • ApoE4[Δ(166-299)] is largely thermodynamically stabilized, whereas apoE4[L28P] is destabilized.

    “ApoE4[(⌬(166 -299)] is largely thermodynamically stabilized (25), whereas apoE4[L28P] is destabilized.”

    From Molecular Basis for Increased Risk for Late-onset Alzheimer Disease Due to the Naturally Occurring L28P Mutation in Apolipoprotein E4 (2014) · cites this paper as [25]

    The Results sections on chemical and thermal unfolding (page unavailable) show that apoE4[Δ(166–299)] loses an unfolding intermediate and unfolds more cooperatively, supporting a stabilization in those respects. But its melting temperature returns to approximately the wild-type value, and the Discussion notes possible destabilization of the N-terminal domain. The citation is attached to the truncation claim, not the separate statement about apoE4[L28P]. (LLM, conf=0.85)

    Experimental — accuracy not yet measured

  • Structural and biophysical properties of apoE can dictate the function of the protein.

    “Several studies have suggested that the structural and biophysical properties of apoE can dictate the function of the protein and have provided insight into the mechanisms by which apoE is involved in cardiovascular and neurological diseases [42], [43], [44], [45], [46], [47], [48], [49].”

    From Biophysical Analysis of Apolipoprotein E3 Variants Linked with Development of Type III Hyperlipoproteinemia (2011) · cites this paper as [43]

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Authors
Chroni, A., Pyrpassopoulos, S., Thanassoulas, A., Nounesis, G., Zannis, V. I., & Stratikos, E.
Affiliations
Boston University (US)
Corresponding author
  • Chroni, Angeliki
  • Stratikos, Efstratios
ORCID
Venue
Biochemistry
Publisher
American Chemical Society (ACS)
Published
2008-08-09
Volume
47
Issue
35
Pages
9071-9080
ISSN
  • 0006-2960 (ISSN-L)
  • 1520-4995
DOI
10.1021/bi800469r
PMC
PMC2692411
OpenAlex
W1998040868
Cited by
26
References
8
Citations by year
2024: 1 · 2023: 1 · 2019: 1 · 2018: 2 · 2016: 1 · 2015: 3 · 2014: 2 · 2013: 2 · 2012: 5
FWCI
1.01
Type
journal article
Language
en
Open access
Locations
  • Biochemistry (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
Funders
National Heart, Lung, and Blood Institute (HL 68216, R01HL068216)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Protein Structure and Dynamics
  • Health Sciences › Medicine › Physiology › Alzheimer's disease research and treatments
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Protein Interaction Studies and Fluorescence Analysis
Keywords
APOE ε4, C-terminal truncation, Alzheimer's disease, protein secondary structure, alpha-helix content, thermal denaturation, unfolding cooperativity, chemical denaturation, hydrophobic sites, solvent accessibility, conformational change
MeSH terms
Circular Dichroism, Humans, Structure-Activity Relationship, Sequence Deletion, Protein Structure, Secondary, Protein Folding, Apolipoprotein E4

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