RESUMO
The Mst-Lats kinase cascade is central to the Hippo tumor-suppressive pathway that controls organ size and tissue homeostasis. The adaptor protein Mob1 promotes Lats activation by Mst, but the mechanism remains unknown. Here, we show that human Mob1 binds to autophosphorylated docking motifs in active Mst2. This binding enables Mob1 phosphorylation by Mst2. Phosphorylated Mob1 undergoes conformational activation and binds to Lats1. We determine the crystal structures of phospho-Mst2-Mob1 and phospho-Mob1-Lats1 complexes, revealing the structural basis of both phosphorylation-dependent binding events. Further biochemical and functional analyses demonstrate that Mob1 mediates Lats1 activation through dynamic scaffolding and allosteric mechanisms. Thus, Mob1 acts as a phosphorylation-regulated coupler of kinase activation by virtue of its ability to engage multiple ligands. We propose that stepwise, phosphorylation-triggered docking interactions of nonkinase elements enhance the specificity and robustness of kinase signaling cascades.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal , Modelos Moleculares , Proteínas Serina-Treonina Quinases/química , Proteínas Serina-Treonina Quinases/fisiologia , Transdução de Sinais , Proteínas Adaptadoras de Transdução de Sinal/química , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Animais , Sítios de Ligação , Células Cultivadas , Cristalização , Drosophila melanogaster , Via de Sinalização Hippo , Humanos , Dados de Sequência Molecular , Fosforilação , Ligação Proteica , Proteínas Serina-Treonina Quinases/metabolismo , Estrutura Quaternária de Proteína , Alinhamento de Sequência , Serina-Treonina Quinase 3RESUMO
The tumor-suppressive Hippo pathway controls tissue homeostasis through balancing cell proliferation and apoptosis. Activation of the kinases Mst1 and Mst2 (Mst1/2) is a key upstream event in this pathway and remains poorly understood. Mst1/2 and their critical regulators RASSFs contain Salvador/RASSF1A/Hippo (SARAH) domains that can homo- and heterodimerize. Here, we report the crystal structures of human Mst2 alone and bound to RASSF5. Mst2 undergoes activation through transautophosphorylation at its activation loop, which requires SARAH-mediated homodimerization. RASSF5 disrupts Mst2 homodimer and blocks Mst2 autoactivation. Binding of RASSF5 to already activated Mst2, however, does not inhibit its kinase activity. Thus, RASSF5 can act as an inhibitor or a potential positive regulator of Mst2, depending on whether it binds to Mst2 before or after activation-loop phosphorylation. We propose that these temporally sensitive functions of RASSFs enable the Hippo pathway to respond to and integrate diverse cellular signals.