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Mol Cell Proteomics. 2017 Jun;16(6):1111-1125. doi: 10.1074/mcp.M117.068130. Epub 2017 Apr 3.

Regulation of Protein Interactions by Mps One Binder (MOB1) Phosphorylation.

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From the ‡Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, Ontario, Canada, M5G 1X5.
§Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada, M5S 1A8.
¶The Institute of Cancer Research, Divisions of Structural Biology and Cancer Biology, London, UK, SW7 3RP.
‖NE-CAT APS, Building 436E, Argonne National Lab, 9700 S. Cass Avenue, Argonne, Illinois 60439.
From the ‡Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, Ontario, Canada, M5G 1X5;
**Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada, M5S 1A8.


MOB1 is a multifunctional protein best characterized for its integrative role in regulating Hippo and NDR pathway signaling in metazoans and the Mitotic Exit Network in yeast. Human MOB1 binds both the upstream kinases MST1 and MST2 and the downstream AGC group kinases LATS1, LATS2, NDR1, and NDR2. Binding of MOB1 to MST1 and MST2 is mediated by its phosphopeptide-binding infrastructure, the specificity of which matches the phosphorylation consensus of MST1 and MST2. On the other hand, binding of MOB1 to the LATS and NDR kinases is mediated by a distinct interaction surface on MOB1. By assembling both upstream and downstream kinases into a single complex, MOB1 facilitates the activation of the latter by the former through a trans-phosphorylation event. Binding of MOB1 to its upstream partners also renders MOB1 a substrate, which serves to differentially regulate its two protein interaction activities (at least in vitro). Our previous interaction proteomics analysis revealed that beyond associating with MST1 (and MST2), MOB1A and MOB1B can associate in a phosphorylation-dependent manner with at least two other signaling complexes, one containing the Rho guanine exchange factors (DOCK6-8) and the other containing the serine/threonine phosphatase PP6. Whether these complexes are recruited through the same mode of interaction as MST1 and MST2 remains unknown. Here, through a comprehensive set of biochemical, biophysical, mutational and structural studies, we quantitatively assess how phosphorylation of MOB1A regulates its interaction with both MST kinases and LATS/NDR family kinases in vitro Using interaction proteomics, we validate the significance of our in vitro studies and also discover that the phosphorylation-dependent recruitment of PP6 phosphatase and Rho guanine exchange factor protein complexes differ in key respects from that elucidated for MST1 and MST2. Together our studies confirm and extend previous work to delineate the intricate regulatory steps in key signaling pathways.

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