Src-homology 3 (SH3) domains bind to proline-rich motifs in target proteins. We
have determined high-resolution crystal structures of the complexes between the
SH3 domains of Abl and Fyn tyrosine kinases, and two ten-residue proline-rich
peptides derived from the SH3-binding proteins 3BP-1 and 3BP-2. The X-ray data
show that the basic mode of binding of both proline-rich peptides is the same.
Peptides are bound over their entire length and interact with three major sites
on the SH3 molecules by both hydrogen-bonding and van der Waals contacts.
Residues 4-10 of the peptide adopt the conformation of a left-handed polyproline
helix type II. Binding of the proline at position 2 requires a kink at the
non-proline position 3.
