Lazzell Diana R, Belizaire Roger, Thakur Pratima, Sherry David M, Janz Roger
WM Keck Center for Learning and Memory, Department of Neurobiology and Anatomy, University of Texas Medical School, Houston, Texas 77030, USA.
J Biol Chem. 2004 Dec 10;279(50):52124-31. doi: 10.1074/jbc.M407502200. Epub 2004 Oct 5.
SV2 proteins are abundant synaptic vesicle proteins expressed in two major (SV2A and SV2B) and one minor (SV2C) isoform. SV2A and SV2B have been shown to be involved in the regulation of synaptic vesicle exocytosis. Previous studies found that SV2A, but not SV2B, can interact with the cytoplasmic domain of synaptotagmin 1, a Ca2+ sensor for synaptic vesicle exocytosis. To determine whether SV2B can interact with full-length synaptotagmin 1, we performed immunoprecipitations from brain protein extracts and found that SV2B interacts strongly with synaptotagmin 1 in a detergent-resistant, Ca2+ -independent manner. In contrast, an interaction between native SV2A and synaptotagmin 1 was not detectable under these conditions. The SV2B-synaptotagmin 1 complex also contained the synaptic t-SNARE proteins, syntaxin 1 and SNAP-25, suggesting that SV2B may participate in exocytosis by modulating the interaction of synaptotagmin 1 with t-SNARE proteins. Analysis of retinae in SV2B knock-out mice revealed a strong reduction in the level of synaptotagmin 1 in rod photoreceptor synapses, which are unique in that they express only the SV2B isoform. In contrast, other synaptic vesicle proteins were not affected by SV2B knock out, indicating a specific role for SV2B in the regulation of synaptotagmin 1 levels at certain synapses. These experiments suggest that the SV2B-synaptotagmin 1 complex is involved in the regulation of synaptotagmin 1 stability and/or trafficking. This study has demonstrated a new role of SV2B as a regulator of synaptotagmin 1 that is likely mediated by direct interaction of these two synaptic proteins.
SV2蛋白是丰富的突触小泡蛋白，以两种主要异构体（SV2A和SV2B）和一种次要异构体（SV2C）形式表达。已证明SV2A和SV2B参与突触小泡胞吐作用的调节。先前的研究发现，SV2A而非SV2B可与突触结合蛋白1的胞质结构域相互作用，突触结合蛋白1是突触小泡胞吐作用的Ca2+传感器。为了确定SV2B是否能与全长突触结合蛋白1相互作用，我们从脑蛋白提取物中进行了免疫沉淀，发现SV2B以一种抗去污剂、不依赖Ca2+的方式与突触结合蛋白1强烈相互作用。相比之下，在这些条件下未检测到天然SV2A与突触结合蛋白1之间的相互作用。SV2B-突触结合蛋白1复合物还包含突触t-SNARE蛋白、 syntaxin 1和SNAP-25，这表明SV2B可能通过调节突触结合蛋白1与t-SNARE蛋白的相互作用参与胞吐作用。对SV2B基因敲除小鼠视网膜的分析显示，视杆光感受器突触中突触结合蛋白1的水平大幅降低，视杆光感受器突触的独特之处在于它们仅表达SV2B异构体。相比之下，其他突触小泡蛋白不受SV2B基因敲除的影响，这表明SV2B在某些突触中对突触结合蛋白1水平的调节具有特定作用。这些实验表明，SV2B-突触结合蛋白1复合物参与突触结合蛋白1稳定性和/或运输的调节。这项研究证明了SV2B作为突触结合蛋白1调节剂的新作用，这可能是由这两种突触蛋白的直接相互作用介导的。
