Marraffini Luciano A, Schneewind Olaf
Departments of Microbiology and Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois 60637, USA.
J Biol Chem. 2005 Apr 22;280(16):16263-71. doi: 10.1074/jbc.M500071200. Epub 2005 Feb 16.
Staphylococcus aureus sortase A cleaves surface protein precursors bearing C-terminal LPXTG motif sorting signals between the threonine and glycine residues. Using lipid II precursor as cosubstrate, sortase A catalyzes the amide linkage between the carboxyl group of threonine and the amino group of pentaglycine cross-bridges, thereby tethering C-terminal ends of surface proteins to the bacterial cell wall envelope. Staphylococcal sortase B also anchors its only known substrate, the IsdC precursor with a C-terminal NPQTN motif sorting signal, to the cell wall envelope. Herein, we determined the cell wall anchor structure of IsdC. The sorting signal of IsdC is cleaved between threonine and asparagine of the NPQTN motif, and the carboxyl group of threonine is amide-linked to the amino group of pentaglycine crossbridges. In contrast to sortase A substrates, the anchor structure of IsdC displays shorter glycan strands and significantly less cell wall cross-linking. A model is proposed whereby sortases A and B recognize unique features of sorting signals and peptidoglycan substrates to deposit proteins with distinct topologies in the cell wall envelope.
金黄色葡萄球菌分选酶A在苏氨酸和甘氨酸残基之间切割带有C端LPXTG基序分选信号的表面蛋白前体。分选酶A以脂质II前体作为共底物，催化苏氨酸的羧基与五甘氨酸交联桥的氨基之间形成酰胺键，从而将表面蛋白的C末端连接到细菌细胞壁包膜上。葡萄球菌分选酶B也将其唯一已知的底物——带有C端NPQTN基序分选信号的IsdC前体锚定到细胞壁包膜上。在此，我们确定了IsdC的细胞壁锚定结构。IsdC的分选信号在NPQTN基序的苏氨酸和天冬酰胺之间被切割，苏氨酸的羧基与五甘氨酸交联桥的氨基形成酰胺键。与分选酶A的底物不同，IsdC的锚定结构显示出较短的聚糖链且细胞壁交联显著减少。我们提出了一个模型，据此分选酶A和B识别分选信号和肽聚糖底物的独特特征，以在细胞壁包膜中沉积具有不同拓扑结构的蛋白质。
