A specific negatively charged sequence confers intramolecular regulation on Munc13-1 function in synaptic exocytosis

• 成果类型: Article
• 署名作者: Zhao, Kexu; Zhang, Li; Lei, Mengshi; Jin, Ziqi; Du, Tianxin; Zhang, Hong; Sheng, Yin; Hu, Zhitao; Wang, Shen; Ma, Cong
• 署名单位: Huazhong University of Science & Technology; Zhengzhou University; Huazhong University of Science & Technology; City University of Hong Kong; Huazhong University of Science & Technology; Huazhong University of Science & Technology; Guangzhou Medical University
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-15258
• DOI: 10.1073/pnas.2508915122
• 发表日期: 2025-06-17
• 关键词: short-term plasticity; active zone; electrostatic interactions; neurotransmitter release; transmitter release; phosphorylation; proteins; complex; mechanisms; receptor

摘要

Munc13 family proteins are crucial for the secretion of neurotransmitters and hormones necessary for cell communication. They share a conserved C-terminal region that includes C2 and the MUN domains, which facilitate membrane interactions and the assembly of soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) complexes. Neuronal isoforms of Munc13 possess a variable N-terminal region that is essential for neurotransmitter release and short-term plasticity, although the precise functions of this region remain not fully understood. Here, we identified a negatively charged sequence within the N terminus of Munc13-1, termed polyE, which is specific to Munc13-1 among all Munc13 isoforms and potentially derived from a common ancestor of homeotherms. We found that polyE binds significantly to the MUN domain through charge-charge interactions, inhibiting MUN activity in promoting SNARE complex assembly. Disrupting the polyE-MUN interaction by introducing pseudophosphorylated mutations in the MUN domain alleviates this inhibition, thereby enhancing neurotransmitter release. Strikingly, Ca2+ ions exhibit significant binding to polyE. We found that 40 mu M of Ca2+ adequately competes with the polyE-MUN interaction to reduce polyE inhibition. This concentration is comparable to presynaptic local [Ca2+]i triggered by a single action potential. Taken together, these results indicate an autoinhibition conformation of Munc13-1 mediated by the polyE-MUN interaction. In addition, the relief of this autoinhibition conformation of Munc13-1 by presynaptic Ca2+ influx and/or posttranslational modifications in the MUN domain may underlie Munc13-1 function in neurotransmitter release and short-term plasticity.