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Structural Differences between the Streptococcus agalactiae Housekeeping and Pilus-Specific Sortases: SrtA and SrtC1

机译:无乳链球菌管家和Pilus特异性分选酶之间的结构差异:SrtA和SrtC1

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摘要

The assembly of pili on the cell wall of Gram-positive bacteria requires transpeptidase enzymes called sortases. In Streptococcus agalactiae, the PI-1 pilus island of strain 2603V/R encodes two pilus-specific sortases (SrtC1 and SrtC2) and three pilins (GBS80, GBS52 and GBS104). Although either pilus-specific sortase is sufficient for the polymerization of the major pilin, GBS80, incorporation of the minor pilins GBS52 and GBS104 into the pilus structure requires SrtC1 and SrtC2, respectively. The S. agalactiae housekeeping sortase, SrtA, whose gene is present at a different location and does not catalyze pilus polymerization, was shown to be involved in cell wall anchoring of pilus polymers. To understand the structural basis of sortases involved in such diverse functions, we determined the crystal structures of S. agalactiae SrtC1 and SrtA. Both enzymes are made of an eight-stranded beta-barrel core with variations in their active site architecture. SrtA exhibits a catalytic triad arrangement similar to that in Streptococcus pyogenes SrtA but different from that in Staphylococcus aureus SrtA. In contrast, the SrtC1 enzyme contains an N-terminal helical domain and a ‘lid’ in its putative active site, which is similar to that seen in Streptococcus pneumoniae pilus-specific sortases, although with subtle differences in positioning and composition. To understand the effect of such differences on substrate recognition, we have also determined the crystal structure of a SrtC1 mutant, in which the conserved DP(W/F/Y) motif was replaced with the sorting signal motif of GBS80, IPNTG. By comparing the structures of WT wild type SrtA and SrtC1 and the ‘lid’ mutant of SrtC1, we propose that structural elements within the active site and the lid may be important for defining the role of specific sortase in pili biogenesis.
机译:菌毛在革兰氏阳性细菌细胞壁上的组装需要称为分选酶的转肽酶。在无乳链球菌中,菌株2603V / R的PI-1菌毛岛编码两个菌毛特异性分选酶(SrtC1和SrtC2)和三个菌毛蛋白(GBS80,GBS52和GBS104)。尽管任一菌毛特异性分选酶都足以聚合主要菌毛GBS80,但将次菌毛GBS52和GBS104掺入菌毛结构中分别需要SrtC1和SrtC2。无乳链球菌管家分选酶SrtA,其基因存在于不同的位置,并且不催化菌毛聚合,被证明参与菌毛聚合物的细胞壁锚定。为了了解参与这种多样化功能的分选酶的结构基础,我们确定了无乳链球菌SrtC1和SrtA的晶体结构。两种酶均由八链β-桶状核心组成,其活性位点结构有所不同。 SrtA具有类似于化脓性链球菌SrtA的催化三联体排列,但不同于金黄色葡萄球菌SrtA的催化三联排列。相反,SrtC1酶在其推定的活性位点中包含一个N末端螺旋结构域和一个“盖子”,这与肺炎链球菌菌毛特异性分选酶中所见的相似,尽管在位置和组成上存在细微的差异。为了了解这种差异对底物识别的影响,我们还确定了SrtC1突变体的晶体结构,其中保守的DP(W / F / Y)主题被GBS80 IPNTG的排序信号主题取代。通过比较野生型野生型SrtA和SrtC1以及SrtC1的“盖子”突变体的结构,我们认为活性位点和盖子中的结构元件对于定义特定分选酶在菌毛生物发生中的作用可能很重要。

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