SH2 domains are a class of protein–protein interaction modules with the function to recognize and bind sequences characterized by the presence of a phosphorylated tyrosine. SHP2 is a protein phosphatase involved in the Ras-ERK1/2 signaling pathway that possess two SH2 domains, namely, N-SH2 and C-SH2, that mediate the interaction of SHP2 with various partners and determine the regulation of its catalytic activity. One of the main interactors of the SH2 domains of SHP2 is Gab2, a scaffolding protein with critical role in determining cell differentiation. Despite their key biological role and the importance of a correct native fold to ensure it, the mechanism of binding of SH2 domains with their ligands and the determinants of their stability have been poorly characterized. In this article, we present a comprehensive kinetic study of the folding of the C-SH2 domain and the binding mechanism with a peptide mimicking a region of Gab2. Our data, obtained at different pH and ionic strength conditions and supported by site-directed mutagenesis, highlight the role of electrostatic interactions in the early events of recognition. Interestingly, our results suggest a key role of a highly conserved histidine residue among SH2 family in the interaction with negative charges carried by the phosphotyrosine of Gab2. Moreover, the analysis of the equilibrium and kinetic folding data of C-SH2 describes a complex mechanism implying a change in rate-limiting step at high denaturant concentrations. Our data are discussed under the light of previous works on N-SH2 domain of SHP2 and other SH2 domains.
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