The function of PTB domain proteins

Phosphotyrosine binding (PTB) domains have been identified in a large numbe r of proteins. In proteins like Shc and IRS-1, the PTB domain binds in a ph osphotyrosine-dependent fashion to peptides that form a beta turn. In these proteins, PTB domains play an important role in signal transduction by gro wth factor receptors. However, in several other proteins, the PTB domains h ave been found to participate in phosphotyrosine-independent interactions. The X11 family of proteins contains a PTB domain that binds peptides in a p hosphotyrosine-independent fashion. The homologue of X11 in C. elegans is t he lin-10 gene, a gene crucial for receptor targeting to the basolateral su rface of body wall epithelia. The X11/Lin-10 proteins are found in a comple x with two other proteins, Lin-2 and Lin-7, which have also been implicated in basolateral targeting in worm epithelia. This protein complex is also l ikely to be important in the targeting of cell surface proteins in mammalia n neurons and epithelia. The ability of the PTB domain to bind peptides in a phosphotyrosine-dependent and -independent fashion allows this domain to be involved in diverse cellular functions.