Determinants of ligand specificity in groups I and IV WW domains

We have applied surface plasmon resonance to determine the ligand specificity of several W W domains containing Arg-14. Among these W W domains, Rsp5.2 and mNedd4.3 bound only to the Group I ligand containing Pro-Pro-Xaa-Tyr with K-D values of 11 and 55 muM, respectively. The WW domains of hPin1, C. elegans Pin1 homologue (Y110), PinA and Ssp1 bound to Group IV ligands with K-D values ranging from 22 to 700 muM. PinA and Ssp1 do not have Arg17, unlike Pin1 and Y110. The modeled structures of PinA and Ssp1 revealed that they conserve the structure and network of hydrogen bonds of Loop 1, which are also formed in Pin1 and Y110. We propose that this configuration of Loop I (referred to as the "p patch") is necessary for binding Group IV ligands, and that it can be used to predict the specificity and functions of other W W domains. In addition, we have completed the back bone assignment of the W W domain of PinA.