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AlphaFold and Implications for Intrinsically Disordered Proteins

Open access
Ruff, Kiersten M., Pappu, Rohit V.·2021·Journal of Molecular Biology

Abstract

Accurate predictions of the three-dimensional structures of proteins from their amino acid sequences have come of age. AlphaFold, a deep learning-based approach to protein structure prediction, shows remarkable success in independent assessments of prediction accuracy. A significant epoch in structural bioinformatics was the structural annotation of over 98% of protein sequences in the human proteome. Interestingly, many predictions feature regions of very low confidence, and these regions largely overlap with intrinsically disordered regions (IDRs). That over 30% of regions within the proteome are disordered is congruent with estimates that have been made over the past two decades, as intense efforts have been undertaken to generalize the structure-function paradigm to include the importance of conformational heterogeneity and dynamics. With structural annotations from AlphaFold in hand, there is the temptation to draw inferences regarding the "structures" of IDRs and their interactomes. Here, we offer a cautionary note regarding the misinterpretations that might ensue and highlight efforts that provide concrete understanding of sequence-ensemble-function relationships of IDRs. This perspective is intended to emphasize the importance of IDRs in sequence-function relationships (SERs) and to highlight how one might go about extracting quantitative SERs to make sense of how IDRs function.

AI snapshot

Written from the paper’s full text.

TL;DR

This perspective cautions against over-interpreting AlphaFold’s low-confidence and “unstructured” annotations for intrinsically disordered regions as literal structures or as failures of prediction. It argues that quantitative sequence–ensemble descriptions, not static models, are needed to understand IDR function.

Key findings

  • AlphaFold annotated over 98% of human proteome sequences, but roughly 30% of residues have pLDDT scores below 50, consistent with estimates that about 30% of the human proteome is disordered.
  • Low-confidence regions largely overlap intrinsically disordered regions (IDRs); the authors argue most are likely genuinely disordered rather than well-folded structures that AlphaFold missed.
  • Static AlphaFold structures of IDRs often overestimate radius of gyration relative to SAXS measurements, as shown for p27 CTD and the hnRNP-A1 prion-like low-complexity domain (A1-LCD).
  • Quantitative ensembles from atomistic simulations vetted by experiments reveal sequence-specific behavior: p27 CTD behaves on average like a Flory random coil, A1-LCD uses aromatic stickers/spacers, and Httex1 prefers tadpole-like conformations with polyQ radius scaling as n^1/3.

Methods

  • Perspective/cautionary note, not primary research; it synthesizes the AlphaFold papers, human proteome annotations, and prior IDP literature.
  • Uses illustrative examples—p27 Kip1 CTD, hnRNP-A1 A1-LCD, and huntingtin exon 1 (Httex1)—comparing AlphaFold static structures with SAXS, NMR, smFRET, and atomistic simulations based on the ABSINTH implicit solvation model and forcefield.
  • Main analysis is interpretive and qualitative, focused on why static AlphaFold depictions of IDRs lack physical meaning and how sequence–ensemble relationships should instead be quantified.

Limitations

  • The paper does not state formal limitations.
  • Evident from the text: it is a perspective/opinion piece, not a systematic review, and its examples are drawn largely from the authors’ own work and close colleagues.
  • Evident from the text: no new experimental data are reported; the quantitative examples rely on previously published simulations and experiments, and the scope is limited to interpreting AlphaFold annotations for IDRs.

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

Integrity signals

Registry

Crossref · 10.1016/j.jmb.2021.167208

Cites

97 of 97 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Claims the paper makes

0 of 58 cited sources checked · 0 supported · 0 flagged

  • Findingcitation

    Integrating SAXS and NMR measurements with simulations suggests that the ensemble of conformations of A1-LCD fluctuates among locally compact regions, globally compact conformations, and expanded conformations.

    “Integrating SAXS and NMR measurements with simulations, suggests that the ensemble of conformations fluctuate among locally compact regions, globally compact conformations, and expanded conformations.88”
    Quote in the paperSubstantial claim0 of 1 sources checked
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  • Findingnone given

    Many AlphaFold predictions feature regions of very low confidence, and these regions largely overlap with intrinsically disordered regions.

    “Interestingly, many predictions feature regions of very low confidence, and these regions largely overlap with intrinsically disordered regions (IDRs).”
    Quote in the paperNot a substantial claim
  • Findingcitation

    The efficiency of T187 phosphorylation does not change monotonically with changes to Rg.

    “However, the efficiency of T187 phosphorylation does not change monotonically with changes to R g .”
    Quote in the paperSubstantial claim
  • Findingnone given

    Roughly 30% of residues across predicted structures in the human proteome tend to have pLDDT scores less than 50.

    “Roughly 30% of the residues across predicted structures in the human proteome tend to have pLDDT scores that are less than 50.”
    Quote in the paperNot a substantial claim
  • Findingcitation

    There is a cryptic motif that is proximal to the primary substrate motif that regulates the efficiency of T187 phosphorylation.

    “Instead, there is a cryptic motif that is proxi-mal to the primary substrate motif that regulates the efficiency of T187 phosphorylation.64”
    Quote in the paperSubstantial claim0 of 1 sources checked
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    Findingcitation

    Modulating the charge patterning changes the mean size of the conformational ensemble of p27 CTD monotonically, consistent with SAXS experiments.

    “Modulating the charge patterning changes the mean size of the conformational ensemble monotonically, consistent with SAXS experiments.64”
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    Findingcitation

    A sizable fraction of the N-terminal region of p27 is predicted to adopt a helical structure by AlphaFold, and this is consistent with experimental characterizations based on NMR spectroscopy.

    “A sizable fraction of the N-terminal region is predicted to adopt a helical structure by Alpha-Fold, and this is consistent with experimental characterizations based on nuclear magnetic resonance (NMR) spectroscopy.85”
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    Findingown data

    Atomistic simulations reproduce the average Rg value measured using SAXS for p27 CTD.

    “Atomistic simulations reproduce the average R g value measured using SAXS.”
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  • May combine two claims.

    Premisecitation

    The ensemble of an IDR is sequence-specific, and the extent of heterogeneity and relative preferences of conformations within the ensemble depend on the primary sequence, solution conditions, and functional contexts.

    “This ensemble is sequence-specific 30,31 and the extent of heterogeneity 36 as well as the relative preferences of conformations within the ensemble will depend on the primary sequence, solution conditions, and functional contexts.”
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  • Probably not a substantial claim: may not pass S2 (checkable), S4 (based).

    Premisenone given

    Disorder implies that a diverse conformational ensemble best describes the region of interest.

    “Instead, disorder implies that a diverse conformational ensemble best describes the region of interest.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Premisecitation

    The N-terminal portion (residues 1-95) of p27 folds upon binding to Cdk2/cyclin A and this leads to kinase inhibition.

    “The N-terminal portion (residues 1-95) folds upon binding to Cdk2/cyclin A and this leads to kinase inhibition.85,86”
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    Premisecitation

    AlphaFold developers state that long regions with pLDDT < 50 adopt a readily identifiable ribbon-like appearance and should not be interpreted as structures but rather as a prediction of disorder.

    “In the current dataset, long regions with pLDDT < 50 adopt a readily identifiable ribbon-like appearance, and should not be interpreted as structures but rather as a prediction of disorder.”
    Quote in the paperSubstantial claim
  • May combine two claims.

    Premisecitation

    Intrinsically disordered regions often evolve more rapidly than ordered regions, and alignments of these regions are generally poorer and involve large gaps and extensions of gaps because orthologous IDRs can span vast sequence lengths.

    “Intrinsically disordered regions often evolve more rapidly than ordered regions and thus alignments of these regions are generally poorer and involve large gaps and extensions of gaps because orthologous IDRs can span vast sequence lengths.9,23,58,60,[68][69][70]”
    Quote in the paperSubstantial claim0 of 1 sources checked
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  • Probably not a substantial claim: may not pass S3 (load-bearing). May combine two claims.

    Premisecitation

    Alleviation of steric clashes leads to a steep decrease in potential energy, and often the local minimum will be situated closest to the region of the steepest drop in energy.

    “Alleviation of steric clashes leads to a steep decrease in the potential energy, and often the local minimum will be situated closest to the region of the steepest drop in energy.72,73”
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    Premisecitation

    Over the past two decades, there has been growing recognition that the sequence-structure-function paradigm must be generalized to account for the role of conformational heterogeneity and conformational dynamics in protein function.

    “Over the past two decades, there has been growing recognition that the sequence-structurefunction paradigm must be generalized to account for the role of conformational heterogeneity and conformational dynamics in protein function.”
    Quote in the paperNot a substantial claim
  • Probably not a substantial claim: may not pass S3 (load-bearing).

    Premisenone given

    AlphaFold was deployed to predict the structures of 98.5% of proteins in the human proteome.

    “created quite a stir when it was deployed to predict the structures of 98.5% of proteins in the human proteome.”
    Quote in the paperNot a substantial claim
  • May combine two claims.

    Interpretationcitation

    Aromatic residues function as cohesive motifs known as stickers that drive single chain compaction as well as phase separation of A1-LCD.

    “leading to the postulate, tested through theory, computations, and experiments, that aromatic residues function as cohesive motifs known as stickers that drive single chain compaction as well as phase separation 88 -the latter through a network of intermolecular interactions.”
    Quote in the paperSubstantial claim0 of 1 sources checked
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  • Classified as probably not a substantial claim. May combine two claims.

    Premisecitation

    Under standard conditions used to study and characterize protein structures, IDPs/IDRs are defined by conformational heterogeneity, and the preference for heterogeneity is encoded in their amino acid sequences.

    “Under standard conditions used to study and characterize protein structures, IDPs/IDRs are defined by conformational heterogeneity, and the preference for heterogeneity is encoded in their amino acid sequences.11,[29][30][31]”
    Quote in the paperSubstantial claim0 of 4 sources checked
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    Premisecitation

    The overall number of distinct conformations, conformational heterogeneity, and relative importance of different conformations within the ensemble are defined by a combination of sequence-encoded short- and long-range interactions as well as modulation by solution conditions.

    “The overall number of distinct conformations in the ensemble, the conformational heterogeneity, in terms of features such as the sizes and shapes sampled, and the relative importance of different conformations within the ensemble are defined by a combination of sequence-encoded short-and long-range interactions 37,38 as well as the modulation of these interactions by solution conditions.39,40”
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    Premisecitation

    Prediction engines are available to identify regions that undergo disorder-to-order, order-to-disorder, and disorder-to-disorder transitions upon binding.

    “Importantly, prediction engines are also available to identify regions that undergo disorder-to-order, order-to-disorder, and disorder-to-disorder transitions upon binding.44”
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    Premisecitation

    The Pro-rich C-terminal region of Httex1 forms a semi-flexible tail.

    “The Pro-rich C-terminal region forms a semi-flexible tail.”
    Quote in the paperSubstantial claim0 of 1 sources checked
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  • Probably not a substantial claim: may not pass S2 (checkable).

    Premisecitation

    IDPs/IDRs are best defined by a heterogeneous ensemble of conformations.

    “IDPs/IDRs are best defined by a heterogeneous ensemble of conformations.36”
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    Interpretationcitation

    The growth of the 'sticky head' with polyQ length mediates homotypic interactions and modulates heterotypic interactions in the cellular context.

    “Taken together with complementary efforts focused on characterizing Httex1 phase behavior, the results obtained from multipronged studies of monomeric Httex1 predict that the growth of the “sticky head” with polyQ length mediates homotypic interactions and modulates heterotypic interactions in the cellular context.94”
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18 of 18

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

  • AlphaFold successfully predicts natively disordered protein regions, and there is a correlation between decrease of pLDDT and propensity to be in a disordered region.

    “Evidence in favor of this point of view is the successful prediction of natively disordered protein regions by AlphaFold and the correlation between the decrease of pLDDT and propensity to be in a disordered region [25].”
  • Like peptides, IDPs and IDRs are best viewed as sampling diverse conformational ensembles rather than one static conformation.

    “like peptides, IDPs and IDRs are best thought of as sampling diverse conformational ensembles rather than a single static conformation42”
  • Ruff et al found radius of gyration values for IDPs/IDR-containing proteins from static AF2 models deviate significantly from SAXS experimental values.

    “Ruff et al showed that radius of gyration values of IDPs / IDR containing proteins calculated using static AF2 models significantly deviates from those experimentally obtained by small-angle X-ray scattering (SAXS)42”
  • Preliminary studies suggest most targets with very low pLDDT (<50) are likely IDPs/IDRs rather than well-folded proteins AF2 fails to predict.

    “Preliminary studies suggest that the majority of targets with very low-confidence score (pLDDT < 50) assigned by AF2 are likely to be IDPs / IDRs rather than well-folded structures that AF2 fails to predict42–44”
  • Some groups used MD simulations to suggest pLDDT and PAE provide information about dynamics and disorder.

    “Some groups have used MD simulations to suggest that pLDDT and PAE metrics provide information on dynamics and disorder42,65”

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.

  • Two different references are numbered 26

    Minor

    The reference list assigns number 26 to both the Miskei et al. and Tóth-Petróczy et al. papers, making citations to reference 26 ambiguous.

1 of 1

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Authors
Ruff, K. M., & Pappu, R. V.
Affiliations
Washington University in St. Louis (US)
Corresponding author
Pappu, Rohit V.
Venue
Journal of Molecular Biology
Publisher
Elsevier BV
Published
2021-10
Volume
433
Issue
20
Pages
167208
ISSN
0022-2836 (ISSN-L)
OpenAlex
W3195375135
Cited by
635
References
103
Citations by year
2026: 97 · 2025: 154 · 2024: 139 · 2023: 144 · 2022: 91 · 2021: 10
FWCI
10.23
Type
journal article
Language
en
Open access
Locations
  • Journal of Molecular Biology (publishedVersion, cc-by-nc-nd)
  • PubMed (publishedVersion)
Funders
National Institutes of Health
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Protein Structure and Dynamics
  • Physical Sciences › Materials Science › Materials Chemistry › Enzyme Structure and Function
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Receptor Mechanisms and Signaling
Keywords
AlphaFold, intrinsically disordered regions, protein structure prediction, sequence-function relationships, conformational heterogeneity, protein dynamics, protein-protein interaction network
MeSH terms
Deep Learning, Animals, Humans, Models, Molecular, Protein Conformation, Protein Folding, Computational Biology, Proteome, Intrinsically Disordered Proteins

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