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.