Structure and function of mGluR3 interactions with beta-arrestins and the membrane.

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PROJECT SUMMARY This proposal contains a comprehensive program to support a transition toward an independent research career focused on understanding how membrane protein function is modulated by interactions with other proteins and phospholipid membranes, and how this modulation impacts cellular processes and is altered in disease-states. This application describes an innovative and ambitious proposal directly tied to my career and training goals. Background: G protein-coupled receptors (GPCR) are membrane proteins that sense extracelluar stimuli and initiate intracellular signaling pathways through interactions with cytosolic G proteins. Classically, GPCRs are thought to undergo a multi-step inactivation and desensitization process via interactions with β-arrestins following hyper-phosphorylation of the intrinsically-disordered GPCR C-terminal domain (CTD). β-arrestins can also initiate distinct signaling cascades in addition to desensitizing and internalizing GPCRs, though the molecular determinants for each pathway are not well understood. This system is further complicated by the presence of two β-arrestin isoforms which are thought to prefer different GPCR CTD phosphorylation patterns and may initiate different cellular pathways. Metabotropic glutamate receptors (mGluR) are dimeric, neuronal GPCRs that are responsible for sensing main excitatory neurotransmitter glutamate both pre- and post-synaptically. Recently a single isoform, mGluR3, was identified to undergo robust β-arrestin-mediated internalization and the β-arrestin- binding region of the CTD was identified. This was the first reported interaction between a dimeric GPCR and β- arrestins, leading to novel questions about complex stoichiometry and structure. This mGluR3-β-arrestin interaction is further complicated by preliminary data indicating that the β-arrestin binding region of the mGluR3 CTD also interacts with the phospholipid membrane. Specific Aims and Research Design: The proposed study investigates the interactions between mGluR3 and both β-arrestins and the membrane using a combination of 1) single-molecule and ensemble fluorescence-based binding methods to investigate the determinants of the formation of mGluR3-β-arrestin complexes, and 2) cryo-electron microscopy and nuclear magnetic resonance spectroscopy to assess the structural features of interactions between mGluR3, β-arrestins, and the membrane. My in vitro and structural findings will be validated using cellular assays and imaging. Findings will inform a K99/R00 proposal aimed to apply the approaches and findings from this F32 research program broadly to other GPCRs and to pursue the functional consequences of GPCR-β-arrestin coupling in in vivo models. Training and Mentoring: Training goals are supported by 1) a team of co-sponsors Drs. Levitz and Eliezer and a close collaborator (Dr. Meyerson) with expertise in biophysical and biochemical research, 2) a rich institutional environment at Weill Cornell Medical College, and 3) scientific meetings, seminars, and planned publications. Impact: The experience gained during this award will serve at the foundation for my independent career as a protein biophysics researcher and for the development of a novel program of membrane protein research.