Hay J C, Hirling H, Scheller R H
Howard Hughes Medical Institute, Department of Molecular and Cellular Physiology, Stanford University Medical Center, Stanford, California 94305-5428, USA.
J Biol Chem. 1996 Mar 8;271(10):5671-9. doi: 10.1074/jbc.271.10.5671.
Vesicle traffic propagates and maintains distinct subcellular compartments and routes secretory products from their site of synthesis to their final destinations. As a basis for the specificity of vesicular transport reactions, each step in the secretory pathway appears to be handled by a distinct set of evolutionarily conserved proteins. Mammalian proteins responsible for vesicle trafficking at early steps in the secretory pathway are not well understood. In this report, we describe rat sec22 (rsec22) and rat bet1 (rbet1), mammalian sequence homologs of yeast proteins identified as mediators of endoplasmic reticulum-to-Golgi protein transport. rsec22 and rbet1 were expressed widely in mammalian tissues, as anticipated for proteins involved in fundamental membrane trafficking reactions. Recombinant rsec22 and rbet1 proteins behaved as integral membrane components of 28 and 18 kDa, respectively, consistent with their primary structures, which contain a predicted transmembrane domain at or near the carboxyl terminus. Recombinant rsec22 and rbet1 had distinct subcellular localizations, with rsec22 residing on endoplasmic reticulum membranes and rbet1 found on Golgi membranes. Studies with brefeldin A and nocodazole indicated that rbet1 function might involve interaction with or retention in the intermediate compartment. The distinct localizations of rsec22 and rbet1 may reflect their participation in opposite directions of membrane flow between the endoplasmic reticulum and Golgi apparatus.
囊泡运输可传播并维持不同的亚细胞区室，还能将分泌产物从其合成位点运输至最终目的地。作为囊泡运输反应特异性的基础，分泌途径中的每一步似乎都由一组独特的、进化上保守的蛋白质来处理。目前对哺乳动物中负责分泌途径早期阶段囊泡运输的蛋白质了解尚少。在本报告中，我们描述了大鼠sec22（rsec22）和大鼠bet1（rbet1），它们是酵母蛋白的哺乳动物序列同源物，已被鉴定为内质网到高尔基体蛋白质运输的介质。正如参与基本膜运输反应的蛋白质所预期的那样，rsec22和rbet1在哺乳动物组织中广泛表达。重组rsec22和rbet1蛋白分别表现为28 kDa和18 kDa的整合膜成分，这与其一级结构一致，其一级结构在羧基末端或附近含有一个预测的跨膜结构域。重组rsec22和rbet1具有不同的亚细胞定位，rsec22定位于内质网膜上，而rbet1则存在于高尔基体膜上。用布雷菲德菌素A和诺考达唑进行的研究表明，rbet1的功能可能涉及与中间区室的相互作用或滞留。rsec22和rbet1的不同定位可能反映了它们在内质网和高尔基体之间膜流的相反方向上的参与情况。
