Structural Characterization of a Phospho‐Switch in the Metastasis Suppressor RKIP (LB189)

Abstract

RKIP is a member of the phosphatidylethanolamine binding protein (PEBP) family with over 400 members. Previous work showed that phosphorylation of S153 was sufficient to alter RKIP binding partners, effectively upregulating the MAP kinase and β‐adrenergic receptor signaling pathways (Granovsky and Rosner, Cell Res., 18:452, 2008). Yet little is known regarding the mechanism by which RKIP phosphorylation regulates these key signaling pathways. Here we propose a three state allosteric model to explain RKIP function. Using NMR, we demonstrate that the RKIP phospho‐switch is associated with a major structural change that can be instigated by breaking a single salt bridge. We also demonstrate that RKIP can dimerize as a result of the phospho‐switch due to formation of disulfide linkages and the functional significance of this oligomerization will be presented. Together these results reveal a novel phospho‐switch that regulates RKIP function and has broad applicability to other PEBP family members throughout evolution.