Department of Biochemistry, University of Oxford, England.
SH3 domains are found in proteins associated with receptor tyrosine kinase signal transduction complexes. The solution structure of the SH3 domain of the 85 kd regulatory subunit of phosphatidylinositol 3-kinase is shown to be a compact beta barrel consisting of five beta strands arranged in two beta sheets of three and two strands. The structure is similar to that of chicken brain alpha spectrin but represents a distinct class of SH3 domain, with an insertion between the second and third beta strands that may influence binding specificity. 1H chemical shift changes induced by complex formation with a synthetic peptide derived from the SH3-binding protein dynamin, together with amino acid sequence comparisons, suggest that the ligand-binding site consists of a hydrophobic surface flanked by two charged loops.