SHC is an adapter protein that has been implicated in Ras activation. Mast cells express two isoforms of 46 and 52 kDa. Both isoforms of SHC have two domains, an N-terminal phosphotyrosine-binding (PTB) domain and a C-terminal SH2 domain that allows Shc to bind to proteins containing phosphorylated tyrosine residues. Following receptor stimulation, SHC is phosphorylated by Src kinases Syk on Y239, Y240 and Y317 (p56 isoform). Both phosphotyrosines Y239 and Y317 creates the binding site for the SH2 domain of GRB2.