Sortase B-anchored surface proteins of S.aureus

描述(由申请人提供)：由金黄色葡萄球菌引起的人类感染是一个严重的治疗挑战，因为出现了抗药性菌株。表面蛋白锚定在金黄色葡萄球菌细胞壁的机制被认为是抗感染治疗的一个可能的靶点。葡萄球菌表面蛋白是以N端信号肽和C端分选信号为前体合成的，含有LPXTG基序和带正电荷的残基。带电残基被认为保留了分泌途径中的表面蛋白，允许在LPXTG基序的苏氨酸(T)和甘氨酸(G)之间进行信号切割。苏氨酸的羧基随后与肽聚糖交叉桥的氨基连接，将表面蛋白的C末端锚定在葡萄球菌的细胞壁上。Ssortase(SrtA)是金黄色葡萄球菌的一种膜锚定转肽酶，负责将带有LPXTG基序的表面蛋白锚定在细胞壁被膜上。 我们在此报告了在革兰氏阳性病原菌中发现的第二种分解酶(SrtB)。 金黄色葡萄球菌，是锚定迄今未知的具有NPQTN基序的表面蛋白所必需的。纯化的srtB在体外可裂解含NPQTN的多肽，srtB突变体在动物感染的持久性方面存在缺陷。SrtB是铁调控基因座的一部分，称为铁反应表面决定簇(ISD)，它还含有一个铁色素转运蛋白和带有NPQTN和LPXTG基序的表面蛋白。因此，细胞壁锚定的表面蛋白和ISD基因似乎参与了一种新的铁获取机制，这对细菌的发病非常重要。本研究旨在研究Ssortase B在将表面蛋白锚定到细胞壁被膜上的作用，并研究srtB介导的细胞壁分离在感染过程中的作用。遗传和生化实验的目的是鉴定NPQTN-分选信号中含有表面蛋白的锚定在细胞壁被膜上所需的基因或基因产物。其他实验检测了ISD基因在铁运输中的生理作用。

DESCRIPTION (provided by applicant): Human infections caused by Staphylococcus aureus present a serious therapeutic challenge due to the appearance of antibiotic-resistant strains. The mechanism of surface protein anchoring to the S. aureus cell wall is examined as a possible target for anti-infective therapy. Staphylococcal surface proteins are synthesized as precursors with an N-terminal signal peptide and a C-terminal sorting signal, containing a LPXTG motif as well as positively charged residues. The charged residues are thought to retain surface proteins within the secretion pathway, allowing sorting signal cleavage between the threonine (T) and the glycine (G) of the LPXTG motif. The carboxyl-group of threonine is subsequently amide-linked to the amino-group of peptidoglycan crossbridges, anchoring the C-terminal ends of surface proteins to the staphylococcal cell wall. Sortase (SrtA), a membrane anchored transpeptidase of S. aureus, is responsible for anchoring surface proteins with a LPXTG motif to the cell wall envelope. We report here the identification of a second sortase (SrtB) in the Gram-positive pathogen Staphylococcus aureus that is required for anchoring of a hitherto unknown surface protein with a NPQTN motif. Purified SrtB cleaves NPQTN-bearing peptides in vitro, and a srtB mutant is defective in the persistence of animal infections. SrtB is part of an iron-regulated locus called iron-responsive surface determinants (isd), which also contains a ferrichrome transporter and surface proteins with NPQTN and LPXTG motifs. Thus, cell wall anchored surface proteins and the isd locus appear to be involved in a novel mechanism of iron acquisition that is important for bacterial pathogenesis. This proposal aims to characterize the role of sortase B in anchoring surface proteins to the cell wall envelope and to study the contribution of SrtB-mediated cell wall sorting during infection. Genetic and biochemical experiments aim at the identification of genes or gene products that are required for the anchoring of NPQTN-sorting signal containing surface proteins to the cell wall envelope. Other experiments examine the physiological role of the isd locus in iron transport.