Nguyen Truong Cuc Quynh, Nestvogel Dennis, Ratai Olga, Schirra Claudia, Stevens David R, Brose Nils, Rhee JeongSeop, Rettig Jens
Institute of Physiology, Saarland University, Building 59, 66421 Homburg/Saar, Germany.
Neurophysiology Group, Max-Planck-Institute of Experimental Medicine, 37075 Göttingen, Germany; Department of Molecular Neurobiology, Max-Planck-Institute of Experimental Medicine, 37075 Göttingen, Germany.
Cell Rep. 2014 Nov 6;9(3):902-9. doi: 10.1016/j.celrep.2014.09.050. Epub 2014 Oct 23.
Priming of secretory vesicles is a prerequisite for their Ca(2+)-dependent fusion with the plasma membrane. The key vesicle priming proteins, Munc13s and CAPSs, are thought to mediate vesicle priming by regulating the conformation of the t-SNARE syntaxin, thereby facilitating SNARE complex assembly. Munc13s execute their priming function through their MUN domain. Given that the MUN domain of Ca(2+)-dependent activator protein for secretion (CAPS) also binds syntaxin, it was assumed that CAPSs prime vesicles through the same mechanism as Munc13s. We studied naturally occurring splice variants of CAPS2 in CAPS1/CAPS2-deficient cells and found that CAPS2 primes vesicles independently of its MUN domain. Instead, the pleckstrin homology domain of CAPS2 seemingly is essential for its priming function. Our findings indicate a priming mode for secretory vesicles. This process apparently requires membrane phospholipids, does not involve the binding or direct conformational regulation of syntaxin by MUN domains of CAPSs, and is therefore not redundant with Munc13 action.
分泌囊泡的引发是其与质膜发生钙离子依赖性融合的前提条件。关键的囊泡引发蛋白，即Munc13s和CAPSs，被认为是通过调节靶标可溶性N-乙基马来酰胺敏感因子附着蛋白受体（t-SNARE） syntaxin的构象来介导囊泡引发的，从而促进SNARE复合体的组装。Munc13s通过其MUN结构域执行引发功能。鉴于分泌的钙离子依赖性激活蛋白（CAPS）的MUN结构域也能结合syntaxin，因此推测CAPSs通过与Munc13s相同的机制引发囊泡。我们在缺乏CAPS1/CAPS2的细胞中研究了CAPS2天然存在的剪接变体，发现CAPS2引发囊泡与其MUN结构域无关。相反，CAPS2的普列克底物蛋白同源结构域似乎对其引发功能至关重要。我们的研究结果表明了一种分泌囊泡的引发模式。这一过程显然需要膜磷脂，不涉及CAPSs的MUN结构域对syntaxin的结合或直接构象调节，因此与Munc13的作用并不冗余。
