The Requirement for Pneumococcal MreC and MreD Is Relieved by Inactivation of the Gene Encoding PBP1a
The Requirement for Pneumococcal MreC and MreD Is Relieved by Inactivation of the Gene Encoding PBP1a
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DOI：
10.1128/jb.05245-11
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发表时间：
2011-08-01
影响因子：
3.2
通讯作者：
Winkler, Malcolm E.
中科院分区：
文献类型：
--
作者：
Land, Adrian D.;Winkler, Malcolm E.
MreC和MreD，沿着与肌动蛋白同源物MreB一起，是维持杆状细菌形状所必需的。杆状细菌中MreCD的耗竭导致球形细胞的形成和抑制突变的积累。卵球菌属细菌，如肺炎链球菌，缺乏MreB同源物，并且S.肺炎MreCD（MreCD（Spn））蛋白是未知的。在大多数链球菌属物种中，mreCD位于pcsB细胞分裂基因的上游，但我们发现mreCD和pcsB是独立转录的。与杆状细菌相似，我们发现mreCD在S的强毒血清型2 D39菌株中是必需的。肺炎链球菌感染，并且MreCD的消耗导致细胞变圆和裂解。相比之下，实验室菌株R6含有允许Delta mreCD突变体生长的抑制子，并且旁路抑制子在D39 Delta mreCD突变体中积累。一类抑制因子消除了A类青霉素结合蛋白1a（PBP1a）的功能。未包封的Delta pbp1a D39突变体的直径小于其pbp1a（+）亲本或Delta pbp2a和Delta pbp1b突变体，后者缺乏其他A类PBP，且未显示Delta mreCD突变的抑制。受抑制的Delta mreCD Delta pbp1a双突变体形成形状异常的细胞，与单个Delta pbp1a突变体相比，一些细胞具有错位的肽聚糖（PG）生物合成。定量Western印迹显示MreC（Spn）是丰富的（每个细胞约8，500个二聚体），并且免疫荧光显微镜（IFM）将MreCD（Spn）定位于分裂细胞的赤道和隔膜，类似于指示PG合成的PBP和PG五肽。这些综合结果与MreCD（Spn）指导外周PG合成并控制PBP1a定位或活性的模型一致。
MreC and MreD, along with the actin homologue MreB, are required to maintain the shape of rod-shaped bacteria. The depletion of MreCD in rod-shaped bacteria leads to the formation of spherical cells and the accumulation of suppressor mutations. Ovococcus bacteria, such as Streptococcus pneumoniae, lack MreB homologues, and the functions of the S. pneumoniae MreCD (MreCD(Spn)) proteins are unknown. mreCD are located upstream from the pcsB cell division gene in most Streptococcus species, but we found that mreCD and pcsB are transcribed independently. Similarly to rod-shaped bacteria, we show that mreCD are essential in the virulent serotype 2 D39 strain of S. pneumoniae, and the depletion of MreCD results in cell rounding and lysis. In contrast, laboratory strain R6 contains suppressors that allow the growth of Delta mreCD mutants, and bypass suppressors accumulate in D39 Delta mreCD mutants. One class of suppressors eliminates the function of class A penicillin binding protein 1a (PBP1a). Unencapsulated Delta pbp1a D39 mutants have smaller diameters than their pbp1a(+) parent or Delta pbp2a and Delta pbp1b mutants, which lack other class A PBPs and do not show the suppression of Delta mreCD mutations. Suppressed Delta mreCD Delta pbp1a double mutants form aberrantly shaped cells, some with misplaced peptidoglycan (PG) biosynthesis compared to that of single Delta pbp1a mutants. Quantitative Western blotting showed that MreC(Spn) is abundant (approximate to 8,500 dimers per cell), and immunofluorescent microscopy (IFM) located MreCD(Spn) to the equators and septa of dividing cells, similarly to the PBPs and PG pentapeptides indicative of PG synthesis. These combined results are consistent with a model in which MreCD(Spn) direct peripheral PG synthesis and control PBP1a localization or activity.