Department of Microbiology, University of Chicago, 920 E. 58th Street, Cummings Life Sciences Center, 707A, Chicago, IL 60637, USA.
Infect Immun. 2010 May;78(5):1895-904. doi: 10.1128/IAI.01165-09. Epub 2010 Feb 22.
The pathogenesis of spotted fever group (SFG) Rickettsia species, including R. conorii and R. rickettsii, is acutely dependent on adherence to and invasion of host cells, including cells of the mammalian endothelial system. Bioinformatic analyses of several rickettsia genomes revealed the presence of a cohort of genes designated sca genes that are predicted to encode proteins with homology to autotransporter proteins of Gram-negative bacteria. Previous work demonstrated that three members of this family, rOmpA (Sca0), Sca2, and rOmpB (Sca5) are involved in the interaction with mammalian cells; however, very little was known about the function of other conserved rickettsial Sca proteins. Here we demonstrate that sca1, a gene present in nearly all SFG rickettsia genomes, is actively transcribed and expressed in R. conorii cells. Alignment of Sca1 sequences from geographically diverse SFG Rickettsia species showed that there are high degrees of sequence identity and conservation of these sequences, suggesting that Sca1 may have a conserved function. Using a heterologous expression system, we demonstrated that production of R. conorii Sca1 in the Escherichia coli outer membrane is sufficient to mediate attachment to but not invasion of a panel of cultured mammalian epithelial and endothelial cells. Furthermore, preincubation of a recombinant Sca1 peptide with host cells blocked R. conorii cell association. Together, these results demonstrate that attachment to mammalian cells can be uncoupled from the entry process and that Sca1 is involved in the adherence of R. conorii to host cells.
斑点热群（SFG）立克次体物种的发病机制，包括康氏立克次体和立氏立克次体，强烈依赖于与宿主细胞（包括哺乳动物内皮系统的细胞）的附着和入侵。对几种立克次体基因组的生物信息学分析表明，存在一组被指定为 sca 基因的基因，这些基因预测编码与革兰氏阴性细菌的自转运蛋白具有同源性的蛋白质。以前的工作表明，该家族的三个成员 rOmpA（Sca0）、Sca2 和 rOmpB（Sca5）参与了与哺乳动物细胞的相互作用；然而，对于其他保守的立克次体 Sca 蛋白的功能知之甚少。在这里，我们证明了几乎所有 SFG 立克次体基因组中都存在的 sca1 基因在康氏立克次体细胞中是活跃转录和表达的。来自地理上多样化的 SFG 立克次体物种的 Sca1 序列的比对表明，这些序列具有高度的序列同一性和保守性，这表明 Sca1 可能具有保守的功能。使用异源表达系统，我们证明了在大肠杆菌外膜中产生的康氏立克次体 Sca1 足以介导对一系列培养的哺乳动物上皮和内皮细胞的附着，但不能介导入侵。此外，用重组 Sca1 肽预先孵育宿主细胞可阻断康氏立克次体细胞的附着。这些结果表明，与哺乳动物细胞的附着可以与进入过程分离，并且 Sca1 参与了康氏立克次体与宿主细胞的附着。
