WW domain tandem-containing proteins such as KIBRA, YAP, and MAGI play critical roles in cell growth and cell polarity via binding to and positioning target proteins in specific subcellular regions. An immense disparity exists between promiscuity of WW domain-mediated target bindings and specific roles of WW domain scaffold proteins in the cell growth regulation. Hence, by measuring the binding constants of many interactions between WW domains, either isolated or in the form of tandem, and their binding targets, we discovered that WW domain tandems of KIBRA and MAGI, but not YAP, bind to specific target proteins with extremely high affinity and exquisite specificity. We determined high-resolution structures of 7 representative WW tandem/target complex structures: four complex st...[ Read more ]

WW domain tandem-containing proteins such as KIBRA, YAP, and MAGI play critical roles in cell growth and cell polarity via binding to and positioning target proteins in specific subcellular regions. An immense disparity exists between promiscuity of WW domain-mediated target bindings and specific roles of WW domain scaffold proteins in the cell growth regulation. Hence, by measuring the binding constants of many interactions between WW domains, either isolated or in the form of tandem, and their binding targets, we discovered that WW domain tandems of KIBRA and MAGI, but not YAP, bind to specific target proteins with extremely high affinity and exquisite specificity. We determined high-resolution structures of 7 representative WW tandem/target complex structures: four complex structures of KIBRA WW tandem with the PY motifs of PTPN14, AMOT, PTPN14, and β-Dystroglycan; MAGI2 WW tandem in complex with Dendrin PY motifs and two complex structures of YAP WW tandem with Dendrin PY motifs. By systematic biochemistry and structural biology analyses, we succeeded in decoding the target binding mechanisms governing the WW tandem-mediated interactions of proteins involved in the cell growth and polarity regulations. Furthermore, we identified over 100 previously unknown target proteins specific for KIBRA and MAGI2/3 WW tandems, including synaptic proteins β-Dystroglycan, JCAD, which suggests that the target recognition mechanisms elucidated here not only can guide the functional studies of WW domain-containing proteins in cell growth and polarity but also other cellular processes including neuronal synaptic signaling. Finally, the results presented in this study may serve as a portal for future studies of WW domain-containing proteins in general.