Regulated vesicle exocytosis is a Ca2+dependent membrane fusion event of key physiological importance for integration of the nervous, endocrine and immune systems. Because of its central role and involvement in disease, it is important to identify the proteins and mechanisms that are utilized for Ca2+regulated vesicle exocytosis. In neural &endocrine cells, the SNARE proteins VAMP-2, Syntaxin-1 &SNAP-25 constitute the core fusion machinery. SNAREs execute fusion by forming trans complexes between docked vesicles and the plasma membrane. However, not all docked vesicles are fusion-competent and a priming step is needed to promote a fusion-ready state. The assembly of SNARE complexes is fundamental to priming but poorly understood. The principal goal of our proposed research is to elucidate vesicle priming reactions. To do so, we will determine the mechanism of proteins that catalyze priming. Genetic studies indicate that Munc-13 and CAPS, which have sequence homology in a MUN domain, mediate vesicle priming possibly in concert with Munc-18. We found that Munc-13 exhibits a novel interaction with Syntaxin by binding the SNARE motif- containing H3 domain, which is different from the previously-suggested N-terminal Syntaxin binding. Further studies of this interaction and its role will likely shift the current paradigm for a molecular model of priming. We will exploit our findings that purified Munc-13 proteins reconstitute priming in permeabilized cells, promote SNARE-dependent liposome fusion, and stimulate SNARE complex formation in vitro to elucidate a new mechanism for Munc-13 function. This mechanism will be critically evaluated in neural, neuroendocrine and mast cells.
The specific aims for this project are 1) To fully characterize Munc-13-Syntaxin interactions and generate mutant proteins deficient in binding;2.) To determine the mechanism by which Munc-13 promotes SNARE complex assembly in vitro;3) To critically assess the functional role of the new Munc-13 mechanism for priming in PC12 neuroendocrine, hippocampal neuronal, and RBL-2H3 mast cells;and 4) To determine how multiple MUN domain proteins (Munc-13 &CAPS) contribute to priming in secretory cells. Completion of the proposed work will provide major new insight into vesicle priming, Munc-13 mechanisms, and the fusion machinery for regulated vesicle exocytosis.

Public Health Relevance

Neurotransmitters, peptide hormones, and inflammatory mediators are secreted from neural, endocrine and mast cells by the regulated fusion of vesicles with the plasma membrane. We will study key protein interactions that are needed to convert vesicles into a fusion-ready state. Because mutations in these proteins result in human disease (e.g., in immune system function), the work will contribute to understanding the underlying basis of these pathologies.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
Project #
Application #
Study Section
Synapses, Cytoskeleton and Trafficking Study Section (SYN)
Program Officer
Malozowski, Saul N
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Wisconsin Madison
Schools of Earth Sciences/Natur
United States
Zip Code
Bruinsma, Stephen; James, Declan J; Quintana Serrano, Melanie et al. (2018) Small molecules that inhibit the late stage of Munc13-4-dependent secretory granule exocytosis in mast cells. J Biol Chem 293:8217-8229
Zhang, Xingmin Aaron; Martin, Thomas F J (2018) High Throughput NPY-Venus and Serotonin Secretion Assays for Regulated Exocytosis in Neuroendocrine Cells. Bio Protoc 8:
Messenger, Scott W; Woo, Sang Su; Sun, Zhongze et al. (2018) A Ca2+-stimulated exosome release pathway in cancer cells is regulated by Munc13-4. J Cell Biol 217:2877-2890
Zhang, Xingmin; Jiang, Shan; Mitok, Kelly A et al. (2017) BAIAP3, a C2 domain-containing Munc13 protein, controls the fate of dense-core vesicles in neuroendocrine cells. J Cell Biol 216:2151-2166
Woo, Sang Su; James, Declan J; Martin, Thomas F J (2017) Munc13-4 functions as a Ca2+ sensor for homotypic secretory granule fusion to generate endosomal exocytic vacuoles. Mol Biol Cell 28:792-808
Chehab, Tarek; Santos, Nina Criado; Holthenrich, Anna et al. (2017) A novel Munc13-4/S100A10/annexin A2 complex promotes Weibel-Palade body exocytosis in endothelial cells. Mol Biol Cell 28:1688-1700
Kabachinski, Greg; Kielar-Grevstad, D Michelle; Zhang, Xingmin et al. (2016) Resident CAPS on dense-core vesicles docks and primes vesicles for fusion. Mol Biol Cell 27:654-68
Petrie, Matt; Esquibel, Joseph; Kabachinski, Greg et al. (2016) The Vesicle Priming Factor CAPS Functions as a Homodimer via C2 Domain Interactions to Promote Regulated Vesicle Exocytosis. J Biol Chem 291:21257-21270
Martin, Thomas F J (2015) PI(4,5)P?-binding effector proteins for vesicle exocytosis. Biochim Biophys Acta 1851:785-93
Yamaga, Masaki; Kielar-Grevstad, D Michelle; Martin, Thomas F J (2015) Phospholipase C?2 Activation Redirects Vesicle Trafficking by Regulating F-actin. J Biol Chem 290:29010-21

Showing the most recent 10 out of 46 publications