Crystal structure of the C-terminal SH2 domain of the p85 alpha regulatorysubunit of phosphoinositide 3-kinase: An SH2 domain mimicking its own substrate

The binding properties of Src homology-2 (SH2) domains to phosphotyrosine ( pY)-containing peptides have been studied in recent years with the elucidat ion of a large number of crystal and solution structures. Taken together, t hese structures suggest a general mode of binding of pY-containing peptides , explain the specificities of different SH2 domains, and may be used to de sign inhibitors of pY binding by SH2 domain-containing proteins. We now rep ort the crystal structure to 1.8 Angstrom resolution of the C-terminal SH2 domain (C-SH2) of the P85 alpha regulatory subunit of phosphoinositide S-ki nase (PI3 K). Surprisingly, the carboxylate group of Asp2 from a neighbouri ng molecule occupies the phosphotyrosine binding site and interacts with Ar g18 (alpha A2) and Arg36 (beta B5), in a similar manner to the phosphotyros ine-protein interactions seen in structures of other SH2 domains complexed with pY peptides. It is the first example of a non-phosphate-containing, no n-aromatic mimetic of phosphotyrosine binding to SH2 domains, and this coul d have implications for the design of substrate analogues and inhibitors. O verall, the crystal structure closely resembles the solution structure, but a number of loops which demonstrate mobility in solution are well defined by the crystal packing. C-SH2 has adopted a binding conformation reminiscen t of the ligand bound N-terminal SH2 domain of PI3K, apparently induced by the substrate mimicking of a neighbouring molecule in the crystal. (C) 1999 Academic Press.