ACERT Highlights: ACERT's Service and Collaborative Projects

National Institute of General Medical Sciences
	National Biomedical Resource for Advanced ESR Spectroscopy

ACERT's Service and Collaborative Projects

Membrane Binding Induces Distinct Structural Signatures in the Mouse Complexin-1C-Terminal Domain

Complexins play a critical role in regulating SNARE-mediated exocytosis of synaptic vesicles. Evolutionary divergences in complexin function have complicated our understanding of the role these proteins play in inhibiting the spontaneous fusion of vesicles. Previous structural and functional characterizations of worm and mouse complexins have indicated the membrane curvature-sensing C-terminal domain of these proteins is responsible for differences in inhibitory function. We have characterized the structure and dynamics of the mCpx1 CTD in the absence and presence of membranes and membrane mimetics using NMR, ESR, and optical spectroscopies. In the absence of lipids, the mCpx1 CTD features a short helix near its N-terminus and is otherwise disordered. In the presence of micelles and small unilamellar vesicles, the mCpx1 CTD forms a discontinuous helical structure in its C-terminal 20 amino acids, with no preference for specific lipid compositions. In contrast, the mCpx1 CTD shows distinct compositional preferences in its interactions with large unilamellar vesicles. These studies identify structural divergences in the mCpx1 CTD relative to the wCpx1 CTD in regions that are known to be critical to the wCpx1 CTD's role in inhibiting spontaneous fusion of synaptic vesicles, suggesting a potential structural basis for evolutionary divergences in complexin function.

Publication: J. Mol. Biol. (web-published, June, 2022) doi: 10.1016/j.jmb.2022.167710

Figure 1. The complexin CTD is essential for complexin regulation of SNARE-mediated exocytosis. (A) Complexin is comprised of four domains, all of which play specific roles in the function of the protein. (B) Through its interactions with and ability to preferentially bind highly curved membranes, the CTD is thought to tether complexin to synaptic vesicles (left) to facilitate its regulatory interactions with the SNARE complex (right). The CTD has been shown to have sub-domains that facilitate its interactions with highly-curved vesicles. Previous structural characterizations of worm complexin 1 (wCpx1) indicate that an amphipathic helix (AH) forms in the presence of highly curved vesicles, while the C-terminal (CT) motif also binds to vesicles but remains unstructured. A second amphipathic helix (AH2) retains structure even in the absence of vesicles. (C) The sequences of the CTDs of worm complexin 1 (above) and mouse complexin 1 (below) reveal little or no conservation between the two, but putative AHand CT-motifs have been identified in the mCpx1 CTD (underlined), in analogy to the motifs previously characterized for the worm protein (bold).

Emily M. Grasso, Mayu S. Terakawa (Department of Biochemistry, Weill Cornell Medicine, New York, NY)
Alex L. Lai (Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY)
Ying Xue Xie, Trudy F. Ramlall (Department of Biochemistry, Weill Cornell Medicine, New York, NY)
Jack H. Freed (Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY)
and David Eliezer (Department of Biochemistry, Weill Cornell Medicine, New York, NY)

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ACERT is supported by grant 1R24GM146107 from the National Institute of General Medical Sciences (NIGMS), part of the National Institutes of Health.

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