Hayward R D, McGhie E J, Koronakis V
Department of Pathology, University of Cambridge, UK.
Mol Microbiol. 2000 Aug;37(4):727-39. doi: 10.1046/j.1365-2958.2000.02027.x.
An early event in Salmonella infection is the invasion of non-phagocytic intestinal epithelial cells. The pathogen is taken up by macropinocytosis, induced by contact-dependent delivery of bacterial proteins that subvert signalling pathways and promote cytoskeletal rearrangement. SipB, a Salmonella protein required for delivery and invasion, was shown to localize to the cell surface of bacteria invading mammalian target cells and to fractionate with outer membrane proteins. To investigate the properties of SipB, we purified the native full-length protein following expression in recombinant Escherichia coli. Purified SipB assembled into hexamers via an N-terminal protease-resistant domain predicted to form a trimeric coiled coil, reminiscent of viral envelope proteins that direct homotypic membrane fusion. The SipB protein integrated into both mammalian cell membranes and phospholipid vesicles without disturbing bilayer integrity, and it induced liposomal fusion that was optimal at neutral pH and influenced by membrane lipid composition. SipB directed heterotypic fusion, allowing delivery of contents from E. coli-derived liposomes into the cytosol of living mammalian cells.
沙门氏菌感染早期的一个事件是侵袭非吞噬性肠道上皮细胞。病原体通过巨胞饮作用被摄取，这是由细菌蛋白的接触依赖性递送诱导的，这些细菌蛋白会破坏信号通路并促进细胞骨架重排。SipB是递送和侵袭所需的一种沙门氏菌蛋白，已显示其定位于侵入哺乳动物靶细胞的细菌的细胞表面，并与外膜蛋白一起分级分离。为了研究SipB的特性，我们在重组大肠杆菌中表达后纯化了天然全长蛋白。纯化后的SipB通过一个预计形成三聚体卷曲螺旋的N端蛋白酶抗性结构域组装成六聚体，这让人联想到指导同型膜融合的病毒包膜蛋白。SipB蛋白整合到哺乳动物细胞膜和磷脂囊泡中，而不破坏双层膜的完整性，并且它诱导脂质体融合，在中性pH值时最适宜，且受膜脂质组成的影响。SipB指导异型融合，使来自大肠杆菌来源脂质体的内容物能够递送到活的哺乳动物细胞的细胞质中。
