pH-dependent self-association of the Src homology 2 (SH2) domain of the Src homologous and collagen-like (SHC) protein

The Src homologous and collagen-like (SHC) protein plays an essential role in signal transduction pathways in that it participates in the chain of events thai leads to the activation of the protein Ras. The crystal structure of the SH2 domain of SHC has been determined using the method of multiple isomorphous replacement at a resolution of 2.5 Å. The SH2 domain of SHC is similar in fold to other SH2 domains. The peptide-binding surfaces resemble that of the SH2 domain of Src in that a deep pocket is formed where the third amino acid C-terminal to the phosphotyrosine can insert. A novel feature e of this structure is the observation of a disulfide bond and an extensive dimer interface between two symmetry-related molecules. Solution studies under reducing conditions using analytical centrifugation and PAGE suggest that the SH2 domain of SHC dimerizes in a pH-dependent manner where low pH conditions (~pH 4.5) are conducive to dimer formation. Dimerization of SHC may have important biological implications in that it may promote the assembly of large heteromultimeric signaling complexes.