Cited by 251Protein Structure and DynamicsMachine Learning in BioinformaticsEnzyme Structure and Function

The DOI matches its Crossref record; 61 of the 62 references it cites were found in a registry or an index; none of the 33 sources its claims cite is checked for support yet.

AlphaFold 2: Why It Works and Its Implications for Understanding the Relationships of Protein Sequence, Structure, and Function

Open access
Skolnick, Jeffrey, Gao, Mu, Zhou, Hongyi, Singh, Suresh·2021·Journal of Chemical Information and Modeling

Abstract

AlphaFold 2 (AF2) was the star of CASP14, the last biannual structure prediction experiment. Using novel deep learning, AF2 predicted the structures of many difficult protein targets at or near experimental resolution. Here, we present our perspective of why AF2 works and show that it is a very sophisticated fold recognition algorithm that exploits the completeness of the library of single domain PDB structures. It has also learned local side chain packing rearrangements that enable it to refine proteins to high resolution. The benefits and limitations of its ability to predict the structures of many more proteins at or close to atomic detail are discussed.

Overview

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Written from the paper’s full text.

TL;DR

This Viewpoint argues that AlphaFold 2 (AF2) succeeds mainly as a sophisticated fold-recognition algorithm that exploits the near-completeness of the single-domain PDB structure library, plus learned local side-chain packing refinement. It also assesses AF2’s human-exome coverage and discusses implications and limits for inferring protein function, ligand binding, and phenotype.

Key findings

  • AF2 often produced models with TM-score > 0.9, while MSA-based methods plateau around TM-score 0.85; TM-score > 0.85 indicates both global fold and details are correct.
  • In human exome predictions, AF2 confidence score correlated with TM-score at 0.67. For low-quality models, only 10% had a closest template with TM-score ≥ 0.55; for good models, 53%; for high-accuracy models, 86%. These trends held with a current PDB library of almost 90,000 structures clustered at 70% sequence identity.
  • Comparing 26,996 consensus human exome sequences, TASSER-VMT predicted at least one domain with TM-score > 0.4 for 89% of sequences; AF2 had confidence >70 for 67.4% and >60 for 86.9%. AF2 added 8.7% of human sequences with confidence >60, and the union provided confident models for at least one domain for 97.5% of human sequences.
  • For ligand homology modeling, low-resolution structures are adequate, with at most a 20% improvement in enrichment factor going from lower resolution (TM-score > 0.4) to crystal structures, because binding sites are generally the most accurately predicted parts of a protein’s structure.

Methods

  • This is a Viewpoint/perspective, not a new AF2 training study. It interprets AF2’s mechanism using prior deep-learning work and structural analyses.
  • The authors used TM-align to generate structural alignments of AF2-predicted human proteins to a 41,000-member PDB library from 2016, and also examined results with a current PDB library of almost 90,000 structures clustered at 70% sequence identity.
  • They analyzed correlations between AF2 confidence scores and TM-score/contact order, binned confidence as <70, 70–90, and >90, and compared AF2 coverage with TASSER-VMT on 26,996 consensus human exome sequences.

Limitations

  • The paper states that structure alone does not provide biochemical function and cannot predict phenotypical function, which often depends on complex interactions among proteins, RNA, DNA, and metabolites.
  • The paper states that AF2 predicts a particular conformational state; if an active conformation is predicted, it may not work for targeting the inactive state. It also notes that AF2 was trained on proteins with particular ions and might not accurately represent binding pockets under other conditions.
  • The paper states that much work remains to establish AF2’s strengths and limitations, including whether it can predict effects of missense mutations, splice variants, chameleon sequences, cryptic pockets, and allosteric transitions. Evident from the text: the analysis is a perspective focused on the human exome and single-domain PDB completeness, and multimeric/multi-domain prediction is discussed as likely but not fully established.

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Integrity signals

Registry

Crossref · 10.1021/acs.jcim.1c01114

Cites

61 of 61 references verified0 citation errors · 0 not checkable

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Claims the paper makes

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  • It may state two separate claims as one. 11
  • Probably not a substantial claim. 1
11 of 11
  • The paper relies on this without support.

    Binding sites are generally the most accurately predicted parts of a protein's structure.

    “The reason is simple; binding sites are generally the most accurately predicted parts of a protein’s structure.”
  • The paper relies on this without support.

    AF2 was trained on proteins having particular ions.

    “Since AF2 was trained on proteins having particular ions, for example, it might not provide an accurate representation of the binding pocket under other conditions.”
2 of 2

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Metadata

Authors
Skolnick, J., Gao, M., Zhou, H., & Singh, S.
Affiliations
  • Georgia Institute of Technology (US)
  • Twilight Design, 4 Adams Road, Kendall Park, New Jersey 08824, United States
Corresponding author
Skolnick, Jeffrey
Venue
Journal of Chemical Information and Modeling
Published
2021-09-29
Volume
61
Issue
10
Pages
4827-4831
ISSN
  • 1549-9596 (ISSN-L)
  • 1549-960X
OpenAlex
W3201869122
Cited by
251
References
62
Citations by year
2026: 28 · 2025: 58 · 2024: 64 · 2023: 66 · 2022: 31 · 2021: 2
FWCI
12.86
Type
journal article
Language
en
Open access
Locations
  • Journal of Chemical Information and Modeling (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
Funders
U.S. Department of Health and Human Services (GM-118039)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Protein Structure and Dynamics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Machine Learning in Bioinformatics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Structural Biology › Enzyme Structure and Function
Keywords
AlphaFold2, protein structure prediction, CASP14, deep learning, protein fold recognition, side-chain packing, sequence-structure-function relationships
MeSH terms
Algorithms, Amino Acid Sequence, Proteins, Protein Folding

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