INTERACTION OF THE P85-SUBUNIT OF PI 3-KINASE AND ITS N-TERMINAL SH2-DOMAIN WITH A PDGF RECEPTOR PHOSPHORYLATION SITE - STRUCTURAL FEATURES AND ANALYSIS OF CONFORMATIONAL-CHANGES

Circular dichroism and fluorescence spectroscopy were used to investigate the structure of the p85alpha subunit of the PI 3-kinase, a closely related p85beta protein, and a recombinant SH2 domain-containing fragment of p85alpha. Significant spectral changes, indicative of a conformational change, were observed on formation of a complex with a 17 residue peptide containing a phosphorylated tyrosine residue. The sequence of this peptide is identical to the sequence surrounding Tyr751 in the kinase-insert region of the platelet-derived growth factor beta-receptor (betaPDGFR). The rotational correlation times measured by fluorescence anisotropy decay indicated that phosphopeptide binding changed the shape of the SH2 domain-containing fragment. The CD and fluorescence spectroscopy data support the secondary structure prediction based on sequence analysis and provide evidence for flexible linker regions between the various domains of the p85 proteins. The significance of these results for SH2 domain-containing proteins is discussed.