Reid J, Fung H, Gehring K, Klebba P E, Nikaido H
Department of Microbiology and Immunology, University of California, Berkeley 94720.
J Biol Chem. 1988 Jun 5;263(16):7753-9.
Porin, a transmembrane protein in the outer membrane of Escherichia coli, exists in a trimeric structure which is not dissociated during sodium dodecyl sulfate-polyacrylamide gel electrophoresis at 25 degrees C. This unusual stability was utilized in the study of the conformational changes which accompany the targeting of porin to the outer membrane. A delay of 16-44 s between completion of synthesis of a monomer and its assembly into a trimer was found from the ratio of monomers to trimers found in exponentially growing cells. Pulse-chase experiments showed that rapid processing of precursor OmpF molecules was followed by assembly into sodium dodecyl sulfate-resistant oligomers with a half-time of 20 s at 30 degrees C. An intermediate in assembly was isolated by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis below 10 degrees C and was identified as a metastable dimer.
孔蛋白是大肠杆菌外膜中的一种跨膜蛋白，以三聚体结构存在，在25℃的十二烷基硫酸钠-聚丙烯酰胺凝胶电泳过程中不会解离。这种不同寻常的稳定性被用于研究孔蛋白靶向外膜时伴随的构象变化。从指数生长细胞中单体与三聚体的比例发现，单体合成完成与其组装成三聚体之间存在16 - 44秒的延迟。脉冲追踪实验表明，前体OmpF分子快速加工后，在30℃下以20秒的半衰期组装成耐十二烷基硫酸钠的寡聚体。在10℃以下通过免疫沉淀和十二烷基硫酸钠-聚丙烯酰胺凝胶电泳分离出组装过程中的一种中间体，鉴定为亚稳二聚体。
