¹H and ¹⁵N assignments and secondary structure of the PI3K SH3 domain

The sequential ¹H and ¹⁵N assignments of the SH3 domain of human phosphatidyl inositol 3'-kinase (PI3K) were determined by a combination of homonuclear and heteronuclear NMR experiments. With the exception of several protons belonging to lysine and proline residues, all proton and proton-bearing amide nitrogen resonances were assigned. Based on the sequential nuclear Overhauser effects (NOEs), ³J_NH-CαH coupling constants and locations of slowly exchanging amide protons, we determined that the secondary structures of the protein consists of six β-strands, two β-turns and four short helices. Additional long range NOEs indicate that these β-strands form two antiparallel β-sheets. The topology of secondary structural elements of the PI3K SH3 domain is similar to those of the SH3 domains from c-Src and α-spectrin, suggesting that the SH3 family has a common tertiary structural motif.