Synaptotagmin-1, quintuple mutant the C2B domain
Synaptotagmin-1 and neuronal SNARE proteins play key roles in evoked synchronous neurotransmitter release. However, it is unknown how they cooperate to trigger synaptic vesicle fusion. Here we report atomic-resolution crystal structures of Ca2+- and Mg2+-bound complexes between synaptotagmin-1 and the neuronal SNARE complex, one of which was determined with diffraction data from an X-ray free electron laser, leading to an atomic-resolution structure with accurate rotamer assignments for many sidechains. The structures revealed several interfaces, including a large, specific, Ca2+-independent, and conserved interface. Tests of this interface by mutagenesis suggest that it is essential for Ca2+-triggered neurotransmitter release in neuronal synapses and for Ca2+-triggered vesicle fusion in a reconstituted system. We propose that this interface forms prior to Ca2+-triggering, and moves en bloc as Ca2+ influx promotes the interactions between synaptotagmin-1 and the plasma membrane, and consequently remodels the membrane to promote fusion, possibly in conjunction with other interfaces.
Q.Zhou, Y.Lai, T.Bacaj, M.Zhao, A.Y.Lyubimov, M.Uervirojnangkoorn, O.B.Zeldin, A.S.Brewster, N.K.Sauter, A.E.Cohen, S.M.Soltis, R.Alonso-Mori, M.Chollet, H.T.Lemke, R.A.Pfuetzner, U.B.Choi, W.I.Weis, J.Diao, T.C.Sudhof, A.T.Brunger, Architecture of the synaptotagmin-SNARE machinery for neuronal exocytosis. Nature 525, 62-67 (2015).

Primary data
5ccj-sf.cif (3.3 MB bytes): deposited structure factors
5CCJ.pdb (1.0 MB bytes): deposited coordinates
Image of the quintuple mutant of Syt1-C2B