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A complete map of affinity and specificity encoding for a partially fuzzy protein interaction

ABSTRACT: Thousands of protein domains encoded in the human genome function by binding up to a million short linear motifs embedded in intrinsically disordered regions of other proteins. How affinity and specificity are encoded in these binding domains and the motifs themselves is not well understood. The evolvability of binding specificity - how rapidly and extensively it can change upon mutation - is also largely unexplored, as is the contribution of ‘fuzzy’ dynamic residues to affinity and specificity in protein-protein interactions. Here we produce the first global map of affinity and specificity encoding in a globular protein domain. Quantifying >200,000 energetic interactions between the domain and ligand allows us to identify 20 major energetically coupled pairs of sites. These are organised into six modules, with the vast majority of mutations in each module only reprogramming specificity for a single position in the ligand. Nine of the major energetic couplings encoding specificity are direct structural contacts and 11 have an allosteric mechanism of action. The dynamic tail of the ligand is more robust to mutation than the structured portion but contributes additively to binding affinity and communicates with structured residues to enable changes in specificity. Our results present how affinity and specificity are encoded in a globular protein domain interacting with a disordered peptide and a direct comparison of the encoding of affinity and specificity in structured and dynamic molecular recognition.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE265816 | GEO | 2024/04/25

REPOSITORIES: GEO

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Project description:Proteins function in crowded cellular environments in which they must bind to specific target proteins but also avoid binding to many other off-target proteins. In large protein families this task is particularly challenging because many off-target proteins have very similar structures. How this specificity of physical protein-protein interactions in cellular networks is encoded and evolves is not very well understood. Here we address the question of specificity-encoding by comprehensively quantifying the effects of all mutations in one protein, JUN, on its binding to all other members of a protein family, the 54 human basic leucine zipper transcription factors. Fitting a global thermodynamic model to the data reveals that most affinity changing mutations equally affect JUN’s propensity to bind to all its interaction partners. Mutations that alter the specificity of binding are much rarer. These specificity-altering mutations are, however, distributed throughout the JUN interaction interface. JUN’s interaction specificity is encoded by both positive determinants that promote on-target interactions and negative determinants that prevent off-target interactions. Indeed, about half of the specificity-defining residues in JUN have dual functions and both promote on-target binding and prevent off-target binding. Whereas nearly all mutations that alter specificity are pleiotropic and also alter the affinity of binding to all interaction partners, the converse is not true with mutations outside of the interface able to tune affinity without affecting specificity. Our results provide the first global view of how mutations in a protein affect binding to all its potential interaction partners and reveal the distributed encoding of specificity and affinity in an interaction interface. They also show how the modular architecture of coiled-coils provides an elegant solution to the challenge of optimising specificity and affinity in a large protein family.

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A complete map of affinity and specificity encoding for a partially fuzzy protein interaction

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