Nmr structure of the n-Sh2 of the p85 subunit of phosphoinositide 3-Kinase complexed to a doubly phosphorylated peptide reveals a second phosphotyrosine binding site.
The N-terminal src homology 2 (SH2) domain of the p85 subunit of
phosphoinositide 3-kinase (PI3K) has a higher affinity for a peptide with two
phosphotyrosines than for the same peptide with only one. This unexpected result
was not observed for the C-terminal SH2 from the same protein. NMR structural
analysis has been used to understand the behavior of the N-SH2. The structure of
the free SH2 domain has been compared to that of the SH2 complexed with a doubly
phosphorylated peptide derived from polyomavirus middle T antigen (MT). The
structure of the free SH2 domain shows some differences from previous NMR and
X-ray structures. In the N-SH2 complexed with a doubly phosphorylated peptide, a
second site for phosphotyrosine interaction has been identified. Further, line
shapes of NMR signals showed that the SH2 protein-ligand complex is subject to
temperature-dependent conformational mobility. Conformational mobility is also
supported by the spectra of the ligand peptide. A binding model which accounts
for these results is developed.
