The WW domain: linking cell signalling to the membrane cytoskeleton.

The WW domain is one of the smallest yet most versatile protein-protein interaction modules. The ability of this simple domain to interact with a number of proline-containing ligands has resulted in a great deal of functional diversity. Most recently it has been shown that WW domain interactions can also be differentially regulated by tyrosine phosphorylation. Here we briefly review WW domain ligands and structure in comparison to SH3 domain ligands and structure and discuss recent findings with regard to the regulation of WW domain interactions by phosphorylation. In particular we describe the potential for differential binding of the b-dystroglycan WW domain ligand by dystrophin or caveolin-3 in skeletal muscle and show how this could act as a switch to alter the relative affinity of the muscle dystroglycan complex for caveolin-3 or dystrophin and utrophin.