PTB domain binding to signaling proteins through a sequence motif containing phosphotyrosine

Src homology 2 (SH2) domains mediate assembly of signaling complexes by binding specifically to tyrosine-phosphorylated proteins. A phosphotyrosine binding (PTB) domain has been identified which also binds specifically to tyrosine-phosphorylated targets, but is structurally different from SH2 domains. Expression cloning was used to identify targets of PTB domains. PTB domains bound to phosphotyrosine within a sequence motif, asparagine-X1-X2-phosphotyrosine (where X represents any amino acid), that is found in many signaling proteins and is not recognized by SH2 domains. Mutational studies indicated that high affinity binding of PTB domains may require a specific conformation of the motif.