Sortase B-anchored surface proteins of S.aureus

描述（由申请人提供）：由于抗生素耐药菌株的出现，金黄色葡萄球菌引起的人类感染给治疗带来了严重的挑战。研究了表面蛋白锚定在金黄色葡萄球菌细胞壁上的机制，作为抗感染治疗的可能靶点。葡萄球菌表面蛋白以n端信号肽和c端分选信号为前体，含有LPXTG基序和带正电的残基。带电残基被认为在分泌途径中保留表面蛋白，允许在LPXTG基序的苏氨酸(T)和甘氨酸(G)之间进行分选信号切割。苏氨酸的羧基随后与肽聚糖的氨基通过酰胺连接，将表面蛋白的c端固定在葡萄球菌细胞壁上。分类酶（SrtA）是金黄色葡萄球菌的一种膜锚定转肽酶，负责将具有LPXTG基序的表面蛋白锚定在细胞壁包膜上。

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.