Barlag Britta, Hensel Michael
Abteilung Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, Barbarastr. 11, Osnabrück 49076, Germany.
Molecules. 2015 Jan 12;20(1):1134-50. doi: 10.3390/molecules20011134.
Salmonella enterica is a Gram-negative, food-borne pathogen, which colonizes the intestinal tract and invades enterocytes. Invasion of polarized cells depends on the SPI1-encoded type III secretion system (T3SS) and the SPI4-encoded type I secretion system (T1SS). The substrate of this T1SS is the non-fimbrial giant adhesin SiiE. With a size of 595 kDa, SiiE is the largest protein of the Salmonella proteome and consists of 53 repetitive bacterial immunoglobulin (BIg) domains, each containing several conserved residues. As known for other T1SS substrates, such as E. coli HlyA, Ca2+ ions bound by conserved D residues within the BIg domains stabilize the protein and facilitate secretion. The adhesin SiiE mediates the first contact to the host cell and thereby positions the SPI1-T3SS to initiate the translocation of a cocktail of effector proteins. This leads to actin remodeling, membrane ruffle formation and bacterial internalization. SiiE binds to host cell apical membranes in a lectin-like manner. GlcNAc and α2-3 linked sialic acid-containing structures are ligands of SiiE. Since SiiE shows repetitive domain architecture, we propose a zipper-like binding mediated by each individual BIg domain. In this review, we discuss the characteristics of the SPI4-T1SS and the giant adhesin SiiE.
肠炎沙门氏菌是一种革兰氏阴性食源性病原体，它定殖于肠道并侵入肠上皮细胞。极性细胞的侵入依赖于SPI1编码的III型分泌系统（T3SS）和SPI4编码的I型分泌系统（T1SS）。该T1SS的底物是非菌毛巨型粘附素SiiE。SiiE大小为595 kDa，是沙门氏菌蛋白质组中最大的蛋白质，由53个重复的细菌免疫球蛋白（BIg）结构域组成，每个结构域包含几个保守残基。正如其他T1SS底物（如大肠杆菌HlyA）一样，BIg结构域内由保守D残基结合的Ca2+离子可稳定蛋白质并促进分泌。粘附素SiiE介导与宿主细胞的首次接触，从而定位SPI1-T3SS以启动一系列效应蛋白的转运。这会导致肌动蛋白重塑、膜皱褶形成和细菌内化。SiiE以凝集素样方式结合宿主细胞顶端膜。GlcNAc和含α2-3连接唾液酸的结构是SiiE的配体。由于SiiE具有重复的结构域架构，我们提出由每个单独的BIg结构域介导拉链样结合。在本综述中，我们讨论了SPI4-T1SS和巨型粘附素SiiE的特性。
