InterPro: IPR013247 SH3, type 3

SH3 (src Homology-3) domains are small protein modules containing approximately 50 amino acid residues [1, 2]. They are found in a great variety of intracellular or membrane-associated proteins [3, 4, 5] for example, in a variety of proteins with enzymatic activity, in adaptor proteins that lack catalytic sequences and in cytoskeletal proteins, such as fodrin and yeast actin binding protein ABP-1.

The SH3 domain has a characteristic fold which consists of five or six beta-strands arranged as two tightly packed anti-parallel beta sheets. The linker regions may contain short helices [6]. The surface of the SH3-domain bears a flat, hydrophobic ligand-binding pocket which consists of three shallow grooves defined by conservative aromatic residues in which the ligand adopts an extended left-handed helical arrangement. The ligand binds with low affinity but this may be enhanced by multiple interactions. The region bound by the SH3 domain is in all cases proline-rich and contains PXXP as a core-conserved binding motif. The function of the SH3 domain is not well understood but they may mediate many diverse processes such as increasing local concentration of proteins, altering their subcellular location and mediating the assembly of large multiprotein complexes [7].

A homologue of the SH3 domain has been found in a number of different bacterial proteins including glycyl-glycine endopeptidase, bacteriocin and some hypothetical proteins.