- The WWC family consists of three proteins‐ KIBRA/WWC1, WWC2, and WWC3. The
three proteins share a similar primary structure and interact with a common set of proteins. Each paralog contains two WW domains which recognize proline‐rich sequences of the type PPxY (P is proline, Y is tyrosine, x is any amino acid). WW domains adopt a three‐stranded antiparallel beta sheet fold, but the WWC proteins are “atypical” in that, the second WW domain (WW2) is unfolded. The WWC proteins are implicated in regulating cell proliferation, organ growth, cell migration, synaptic signaling and generally thought to perform overlapping functions in most tissues. However, in recent years, several studies point to unique functions for each paralog. This study presents data that suggest that the unique functions arise from differences in binding mechanisms. Constructs of the WW domains of KIBRA and WWC3 and the PPxY segments of four putative binding partners, Large tumor suppressor 1 (LATS1), Angiomotin-like 1 (AMOTL1), DENDRIN, and Synaptopodin (SYNPO) were cloned and over-expressed in E.coli. Binding affinities and binding-induced structural changes were determined by isothermal titration calorimetry (ITC), fluorescence spectroscopy (FS) and nuclear magnetic resonance spectroscopy (NMR). The ITC data show that the LATS1, DENDRIN, and AMOTL1 polypeptides bind the KIBRA WW domains with a higher affinity than the WWC3 WW domains. The FS and NMR data further show that the binding of LATS1 and SYNPO to KIBRA and WWC3 does not induce folding of the WW2 domain, however, mutant LATS1 and SYNPO constructs, designed to mimic the short linker between the DENDRIN PPxY sites, induced folding of the KIBRA and WWC3 WW2 domains. The results suggest that differences in binding affinities for partner proteins and/or binding-induced folding may contribute to the unique functions of the WWC proteins.