Kline Kimberly A, Kau Andrew L, Chen Swaine L, Lim Adeline, Pinkner Jerome S, Rosch Jason, Nallapareddy Sreedhar R, Murray Barbara E, Henriques-Normark Birgitta, Beatty Wandy, Caparon Michael G, Hultgren Scott J
Department of Molecular Microbiology, Washington University School of Medicine, 660 S. Euclid Ave., Campus Box 8230, Saint Louis, MO 63110-1093, USA.
J Bacteriol. 2009 May;191(10):3237-47. doi: 10.1128/JB.01837-08. Epub 2009 Mar 13.
Pathogenic streptococci and enterococci primarily rely on the conserved secretory (Sec) pathway for the translocation and secretion of virulence factors out of the cell. Since many secreted virulence factors in gram-positive organisms are subsequently attached to the bacterial cell surface via sortase enzymes, we sought to investigate the spatial relationship between secretion and cell wall attachment in Enterococcus faecalis. We discovered that sortase A (SrtA) and sortase C (SrtC) are colocalized with SecA at single foci in the enterococcus. The SrtA-processed substrate aggregation substance accumulated in single foci when SrtA was deleted, implying a single site of secretion for these proteins. Furthermore, in the absence of the pilus-polymerizing SrtC, pilin subunits also accumulate in single foci. Proteins that localized to single foci in E. faecalis were found to share a positively charged domain flanking a transmembrane helix. Mutation or deletion of this domain in SrtC abolished both its retention at single foci and its function in efficient pilus assembly. We conclude that this positively charged domain can act as a localization retention signal for the focal compartmentalization of membrane proteins.
致病性链球菌和肠球菌主要依靠保守的分泌（Sec）途径将毒力因子转运并分泌到细胞外。由于革兰氏阳性菌中的许多分泌型毒力因子随后会通过分选酶附着在细菌细胞表面，因此我们试图研究粪肠球菌中分泌与细胞壁附着之间的空间关系。我们发现分选酶A（SrtA）和分选酶C（SrtC）在肠球菌的单个位点与SecA共定位。当SrtA缺失时，经SrtA加工的底物聚集物质在单个位点积累，这意味着这些蛋白质有一个单一的分泌位点。此外，在缺乏菌毛聚合SrtC的情况下，菌毛蛋白亚基也会在单个位点积累。在粪肠球菌中定位于单个位点的蛋白质被发现共享一个位于跨膜螺旋两侧的带正电荷结构域。SrtC中该结构域的突变或缺失消除了其在单个位点的保留及其在有效菌毛组装中的功能。我们得出结论，这个带正电荷的结构域可以作为膜蛋白焦点分隔的定位保留信号。
