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bioRxiv · 10.64898/2026.11.12.766256

Functional mapping of synaptotagmin 1 Ca2+ ligands that mediate excitation-secretion coupling in neurons

Mishra, S.·Mehta, N.·Dominguez, M. J.·Beckett, E. R.·Wozney, M.·Vukovic, A.·Sutton, R. B.·Chapman, E. R.
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Abstract

Synaptotagmin (SYT) 1 is a Ca2+ sensor that triggers rapid synaptic vesicle exocytosis, but how it is activated by Ca2+ remains enigmatic. SYT1 contains two Ca2+-sensing motifs, C2A and C2B. Structural studies have proposed that five acidic residues in each C2 domain mediate Ca2+-binding, but their functional relevance remains unclear. Here, we mutated each of the ten putative ligands and conducted side-by-side comparisons of Ca2+-binding activity and evoked glutamate release. Remarkably, all ten putative ligands are crucial for evoked synchronous release, overturning the view that binding of Ca2+ to C2A is dispensable. Importantly, Ca2+ binding to C2B is essential for synchronization. Furthermore, we report that two new human mutations, corresponding to Ca2+ ligands in C2B, are dominant-negative. Finally, four new crystal structures reveal how the choice of neutralizing substitution differentially alters SYT1 structure and, consequently, function.

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Mishra, S., Mehta, N., Dominguez, M. J., Beckett, E. R., Wozney, M., Vukovic, A., Sutton, R. B., Chapman, E. R.. 2026-11-13. Functional mapping of synaptotagmin 1 Ca2+ ligands that mediate excitation-secretion coupling in neurons. https://doi.org/10.64898/2026.11.12.766256

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