Structural Analysis and Functional Implications of the Negative mTORCl Regulator REDD1

REDD1 is a conserved stress-response protein that regulates mTORCl, a critical I-C regulator of cell growth and proliferation that is implicated in cancer. REDD1 Is Induced by hypoxia, and REDDI overexpression is sufficient to inhibit mTORCl. mFORCl Is regulated by file small GTPase Rheb, which H) in-turn is regulated by the GTPase-activating protein complex, TSC1/TSC2. REDDI induced-m-FORCl Inhibition requires the TSC1/TSC2 complex, and REDDI has been proposed to act by directly binding to and sequestering 14-3-3 proteins away from TSC2 leading to TSC2-depedent inhibition of mTORCl. Structure/function analyses have led LIS to identify two segments in REDD1 that are essential for function which act in an interdependent manner. We have determined a crystal structure of REDDI at 2.0 angstrom resolution, Which shows (flat these two segments fold together to form an Intact domain with a novel fold. This domain is characterized by an alpha/beta Sandwich consisting of two antiparallel alpha-helices and a mixed -shcct encompassing an uncommon psi-loop motif, Structure-based docking and functional analyses suggest that REDDI does not directly bind to 14-3-3 proteins. Sequence conservation mapping to the surface of the structure and mutagenesis studies demarcated I hotspot likely to interact with effector Proteins that is essential for REDDI-i-mediated mTORCl inhibition.