Protein Tagging for High Resolution Structural Analysis of Synaptic Protein Complexes Using Clickable CryoEM Grids

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Project Summary/Abstract In normal learning and memory, dynamic changes in the strength of synaptic connections (called synaptic plasticity) are brought about through exquisite coordination of neurotransmitter release, protein synthesis, protein localization and cytoskeletal reorganization. The timing, magnitude, and location of these processes are determined by protein binding and enzyme activation events within protein signaling networks. In many neurological disorders the spatial and temporal regulations of these protein interactions are disrupted. Thus, in order to effectively design treatments for these complex disorders, detailed information about the spatial organization of protein signaling molecules is absolutely necessary. Current experimental paradigms of qualitative studies with knock-down, overexpression or mutation of particular proteins in mutant animals or in cell lines alone are not adequate to advance our knowledge to the necessary level of mechanistic detail. To address this gap, we are simultaneously developing: 1) a protein labeling technique that is site-specifically and covalently tags a protein with click chemistry functionality and 2) a novel non-fouling, click chemistry- functionalized transmission electron microscopy (TEM) grid coating. The grid coating will enable selective covalent capture of the tagged protein alone and in complex with its interacting proteins onto TEM grids for cryo-EM imaging. This allows to fine control over the reaction, wash, and incubation conditions that the proteins are subjected to, thus allowing control over i) the state of activation of the protein of interest, ii) the surface deposition of the protein, and iii) the binding of the protein with its associated proteins. In addition the TEM grid coatings are non-fouling and thus minimize non-specific binding interactions that would otherwise obscure protein complex identification. Direct imaging of the complexes will be performed using cryo-EM; this maintains proteins in their naturally hydrated state and allows for large protein complexes to be imaged at high resolution. Single particle analysis will be performed to reconstruct the complexes to sub-nanometer resolution.