Katagiri H, Terasaki J, Murata T, Ishihara H, Ogihara T, Inukai K, Fukushima Y, Anai M, Kikuchi M, Miyazaki J
Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
J Biol Chem. 1995 Mar 10;270(10):4963-6. doi: 10.1074/jbc.270.10.4963.
munc-18/n-Sec1/rbSec1, a brain homologue of the yeast Sec1p protein, is thought to participate in regulating the docking and fusion of synaptic vesicles. We have screened the mouse cDNA library of an MIN6 cell line, derived from pancreatic beta cells, for its novel isoform and have identified a cDNA encoding a 593-amino acid protein having 63, 53, and 30% identity with munc-18/n-Sec1/rbSec1, Caenorhabditis elegans unc18, and Saccharomyces cerevisiae Sec1p, respectively. While munc-18/n-Sec1/rbSec1 expression has been reported to be neural-specific, RNA blot analysis has revealed that the novel isoform, which we refer to as muSec1 (mammalian ubiquitous Sec1), is expressed ubiquitously. We have also identified mouse munc-18/n-Sec1/rbSec1 from the MIN6 cDNA library, indicating that different isoforms of a protein participating in vesicular transport exist in a single cell. muSec1 bound to glutathione S-transferase-syntaxin 1A and, although with lower affinity, to glutathione S-transferase-syntaxin 4 fusion protein. These findings suggest that muSec1 is, via its binding to the syntaxin family, involved in the protein trafficking from the Golgi apparatus to the plasma membrane and that the fundamental mechanisms of protein trafficking have been conserved from yeast through virtually all mammalian cells.
munc-18/n-Sec1/rbSec1是酵母Sec1p蛋白的一种脑同源物，被认为参与调节突触小泡的对接和融合。我们从源自胰腺β细胞的MIN6细胞系的小鼠cDNA文库中筛选其新的异构体，并鉴定出一个编码593个氨基酸的蛋白质的cDNA，该蛋白质与munc-18/n-Sec1/rbSec1、秀丽隐杆线虫unc18和酿酒酵母Sec1p的同源性分别为63%、53%和30%。虽然据报道munc-18/n-Sec1/rbSec1的表达具有神经特异性，但RNA印迹分析表明，我们称为muSec1（哺乳动物普遍存在的Sec1）的新异构体在各处均有表达。我们还从MIN6 cDNA文库中鉴定出小鼠munc-18/n-Sec1/rbSec1，这表明参与囊泡运输的一种蛋白质的不同异构体存在于单个细胞中。muSec1与谷胱甘肽S-转移酶-突触融合蛋白1A结合，并且尽管亲和力较低，但也与谷胱甘肽S-转移酶-突触融合蛋白4结合。这些发现表明，muSec1通过与突触融合蛋白家族结合，参与从高尔基体到质膜的蛋白质运输，并且蛋白质运输的基本机制从酵母到几乎所有哺乳动物细胞都是保守的。
