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Distinct domains of complexin I differentially regulate neurotransmitter release

Abstract

Complexins constitute a family of four synaptic high-affinity SNARE complex–binding proteins. They positively regulate a late, post-priming step in Ca2+-triggered synchronous neurotransmitter release, but the underlying molecular mechanisms are unclear. We show here that SNARE complex binding of complexin I (CplxI) via its central α-helix is necessary but, unexpectedly, not sufficient for its key function in promoting neurotransmitter release. An accessory α-helix on the N-terminal side of the SNARE complex–binding region has an inhibitory effect on fast synaptic exocytosis, whereas sequences N-terminally adjacent to this helix facilitate Ca2+-triggered release even in the absence of the Ca2+ sensor synaptotagmin-1. Our results indicate that distinct functional domains of CplxI differentially regulate synaptic exocytosis and that, through the interplay between these domains, CplxI carries out a crucial role in fine-tuning Ca2+-triggered fast neurotransmitter release.

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Figure 1: Overexpression of CplxI rescues CplxI/II DKO neurons.
Figure 2: Synaptic function is not sensitive to CplxI abundance.
Figure 3: Identification of mutations in CplxI that block SNARE complex binding.
Figure 4: Rescue of CplxI/II DKO neurons with SNARE complex binding–deficient CplxI mutants.
Figure 5: SNARE complex binding and function of CplxI N-terminal mutants.
Figure 6: Overexpression of CplxI N-terminal mutants in WT neurons.
Figure 7: Effects of overexpression of WT CplxI and CplxI27–134 in Syt1 KO neurons.
Figure 8: Model for complexin function in Ca2+-triggered neurotransmitter release.

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Acknowledgements

We thank H. Chen, T. Hellmann, I. Herfort, D. Reuter, S. Wenger and A. Zeuch for excellent technical assistance; F. Benseler, D. Schwerdtfeger and I. Thanhäuser for DNA sequencing and oligonucleotide synthesis; R. Nehring and R. Atkinson for technical advice; H. Bellen for comments on the manuscript and E. Neher for continuous support and advice. This work was supported by the Deutsche Forschungsgemeinschaft (SFB 523/B9 to N.B. and C.R.), a Heisenberg Fellowship (to C.R.), the Brown Foundation (to C.R.), the US National Institutes of Health (NS50655 to C.R., NS37200 to J.R.) and Baylor Research Advocates for Student Scientists and a McNair Fellowship (both to H.-T.C.).

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Correspondence to Nils Brose or Christian Rosenmund.

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Supplementary Figures 1–4, Supplementary Data, Supplementary Methods (PDF 4243 kb)

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Xue, M., Reim, K., Chen, X. et al. Distinct domains of complexin I differentially regulate neurotransmitter release. Nat Struct Mol Biol 14, 949–958 (2007). https://doi.org/10.1038/nsmb1292

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