Structure-function study of mammalian Munc18-1 and C. elegans UNC-18 implicates domain 3b in the regulation of exocytosis
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Munc18-1 is an essential synaptic protein functioning during multiple stages of the exocytotic process including vesicle recruitment, docking and fusion. These functions require a number of distinct syntaxin-dependent interactions; however, Munc18-1 also regulates vesicle fusion via syntaxin-independent interactions with other exocytotic proteins. Although the structural regions of the Munc18-1 protein involved in closed-conformation syntaxin binding have been thoroughly examined, regions of the protein involved in other interactions are poorly characterised. To investigate this we performed a random transposon mutagenesis, identifying domain 3b of Munc18-1 as a functionally important region of the protein. Transposon insertion in an exposed loop within this domain specifically disrupted Mint1 binding despite leaving affinity for closed conformation syntaxin and binding to the SNARE complex unaffected. The insertion mutation significantly reduced total amounts of exocytosis as measured by carbon fiber amperometry in chromaffin cells. Introduction of the equivalent mutation in UNC-18 in Caenorhabditis elegans also reduced neurotransmitter release as assessed by aldicarb sensitivity. Correlation between the two experimental methods for recording changes in the number of exocytotic events was verified using a previously identified gain of function Munc18-1 mutation E466K (increased exocytosis in chromaffin cells and aldicarb hypersensitivity of C. elegans). These data implicate a novel role for an exposed loop in domain 3b of Munc18-1 in transducing regulation of vesicle fusion independent of closed-conformation syntaxin binding.
Graham , M E , Prescott , G R , Johnson , J R , Jones , M , Walmesley , A , Haynes , L P , Morgan , A , Burgoyne , R D & Barclay , J W 2011 , ' Structure-function study of mammalian Munc18-1 and C. elegans UNC-18 implicates domain 3b in the regulation of exocytosis ' PLoS One , vol 6 , no. 3 , e17999 . DOI: 10.1371/journal.pone.0017999
© 2011 Graham et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
This work was supported by grants from the Wellcome Trust and BBSRC. GRP was supported by a Wellcome Trust Prize Studentship. The C. elegans strain used in this work was provided by the Caenorhabditis Genetics Center, which is funded by the National Institutes of Health National Center for Research Resources (NCRR). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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