Abstract
Munc13-1 plays a crucial role in neurotransmitter release. We recently proposed that the C-terminal region encompassing the C1, C2B, MUN and C2C domains of Munc13-1 (C1C2BMUNC2C) bridges the synaptic vesicle and plasma membranes through interactions involving the C2C domain and the C1-C2B region. However, the physiological relevance of this model has not been demonstrated. Here we show that C1C2BMUNC2C bridges membranes through opposite ends of its elongated structure. Mutations in putative membrane-binding sites of the C2C domain disrupt the ability of C1C2BMUNC2C to bridge liposomes and to mediate liposome fusion in vitro. These mutations lead to corresponding disruptive effects on synaptic vesicle docking, priming, and Ca2+-triggered neurotransmitter release in mouse neurons. Remarkably, these effects include an almost complete abrogation of release by a single residue substitution in this 200 kDa protein. These results show that bridging the synaptic vesicle and plasma membranes is a central function of Munc13-1.
Highlights
The release of neurotransmitters by Ca2+-triggered synaptic vesicle exocytosis is crucial for interneuronal communication
These results demonstrate that the Munc13-1 C2C domain plays a critical role in synaptic exocytosis, in agreement with previous results (Liu et al, 2016; Madison et al, 2005; Stevens et al, 2005), and show that this role is important for vesicle priming and crucial for evoked neurotransmitter release
Great advances have been recently made in understanding the mechanism of neurotransmitter release, including the fundamental concept that Munc18-1 and Munc13s orchestrate soluble NSF attachment proteins (SNAPs) receptors (SNAREs) complex assembly in an N-ethylmaleimide sensitive factor (NSF)-SNAP-resistant manner (Ma et al, 2013) that explains at least in part the total abrogation of neurotransmitter release observed in the absence of Munc18-1 or Munc13s (Richmond et al, 1999; Varoqueaux et al, 2002; Verhage et al, 2000)
Summary
The release of neurotransmitters by Ca2+-triggered synaptic vesicle exocytosis is crucial for interneuronal communication. Reconstitution studies of synaptic vesicle fusion and vesicle clustering assays suggested that the C2C domain binds to membranes, leading to a model whereby the conserved Munc C-terminal region bridges the synaptic vesicle and plasma membranes through respective interactions with the C2C domain and the C1-C2B region on opposite ends of the MUN domain (Liu et al, 2016) (Figure 1—figure supplement 1). A single point mutation in a 200 kDa protein such as Munc practically abolishes evoked neurotransmitter release, demonstrating the crucial importance of the membrane bridging activity for Munc function and for the sequence of events that lead to synaptic vesicle fusion
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
