Part 1: Proline-binding domains beyond SH3
1.WW Domain
• Description: This domain recognizes proline-rich sequences, typically motifs like PPxY or
[pS/pT] P, to mediate protein-protein interactions in signaling pathways.
• Reference: Mayer, B. J. (2005). Who's on first? Promoting protein–protein interactions
with WW domains. Science Signaling, 2005(282), pe14.
2. EVH1 (Ena/VASP homology 1) domain
• Description: The EVH1 domain recognizes proline-rich peptides containing FPPPP
motifs and mediates protein–peptide interactions involved in cytoskeletal regulation.
• Reference: Ball, L. J., et al. (2002). Structure and binding properties of the EVH1
domain. (2002). EMBO Journal, 21(15), 3989–3999.
Part 2: Why proline is common in binding motifs
1. Structural Constraint and Reduced Entropic Cost
Proline's cyclic side chain restricts its backbone dihedral angles, naturally favoring the adoption
of a polyproline type II (PPII) helix. This rigid, pre-organized structure means the peptide does
not need to fold into shape upon meeting its partner; this reduces the entropic penalty of
binding, thereby increasing the overall binding affinity and facilitating specific recognition by
protein domains.
2. Physicochemical Accessibility and Backbone Properties
Unlike other amino acids, proline lacks a backbone amide hydrogen, which prevents it from
participating in the standard hydrogen-bonding networks of alpha-helices or beta-sheets.
Consequently, proline-rich segments often remain in extended, solvent-exposed conformations
rather than being buried within the protein core. This ensures the motif is highly accessible for
interaction with external binding domains
