Heterodimerization of UNC-13/RIM regulates synaptic vesicle release probability but not priming in C. elegans
Haowen Liu,
Lei Li,
Daniel Nedelcu,
Qi Hall,
Lijun Zhou,
Wei Wang,
Yi Yu,
Joshua M Kaplan,
Zhitao Hu
Affiliations
Haowen Liu
Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Australia
Lei Li
Clem Jones Centre for Ageing Dementia Research, Queensland Brain Institute, The University of Queensland, Brisbane, Australia
Daniel Nedelcu
Department of Molecular Biology, Massachusetts General Hospital, Boston, United States; Department of Neurobiology, Harvard Medical School, Boston, United States
Qi Hall
Department of Molecular Biology, Massachusetts General Hospital, Boston, United States; Department of Neurobiology, Harvard Medical School, Boston, United States
UNC-13 proteins play an essential role in synaptic transmission by recruiting synaptic vesicles (SVs) to become available for release, which is termed SV priming. Here we show that the C2A domain of UNC-13L, like the corresponding domain in mammalian Munc13-1, displays two conserved binding modes: forming C2A/C2A homodimers, or forming a heterodimer with the zinc finger domain of UNC-10/RIM (C2A/RIM). Functional analysis revealed that UNC-13L’s C2A promotes synaptic transmission by regulating a post-priming process. Stimulus-evoked release but not SV priming, was impaired in unc-10 mutants deficient for C2A/RIM heterodimerization, leading to decreased release probability. Disrupting C2A/C2A homodimerization in UNC-13L-rescued animals had no effect on synaptic transmission, but fully restored the evoked release and the release probability of unc-10/RIM mutants deficient for C2A/RIM heterodimerization. Thus, our results support the model that RIM binding C2A releases UNC-13L from an autoinhibitory homodimeric complex to become fusion-competent by functioning as a switch only.
