Absence of pneumococcal PcsB is associated with overexpression of LysM domain-containing proteins
Absence of pneumococcal PcsB is associated with overexpression of LysM domain-containing proteins
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DOI：
10.1099/mic.0.045211-0
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发表时间：
2011-07-01
期刊：
影响因子：
2.8
通讯作者：
Nagy, Eszter
中科院分区：
文献类型：
--
作者：
Giefing-Kroell, Carmen;Jelencsics, Kira E.;Nagy, Eszter
基于序列基序和表现出细胞分离缺陷的基因缺失突变细胞的表型改变，预测细胞分离B所需的链球菌蛋白（PcsB）在肽聚糖代谢中发挥重要作用。然而，到目前为止，还没有发现PcsB的酶活性。通过在四种不同的遗传背景下产生基因缺失突变株，我们可以证明pcsB对肺炎链球菌的细胞存活不是必需的，但对正常的细胞分裂是必需的。缺失突变细胞由于细胞分裂异常、生长减少和对抗生素的敏感性降低而显示出簇状结构，而这些通过携带pcsB的质粒转化完全恢复。免疫荧光染色显示PcsB定位于细胞极点，类似于PBP3和LytB，具有子细胞分离所需的肽聚糖降解活性的酶。与其他PcsB同源物的研究类似，我们无法在体外检测重组或天然肺炎球菌PcsB的肽聚糖裂解活性。除了隔膜放置和分离的缺陷外，PcsB的缺失还诱导了几种蛋白质的释放增加，如烯醇化酶、MaIX和SP0107 LysM结构域蛋白。有趣的是，编码含LysM结构域蛋白的基因存在于肺炎球菌基因组（SP0107和SP2063）中，预计与细胞壁代谢有关，在两种不同遗传背景的Delta pcsB细胞中被发现高度过表达（增加14-33倍）。除此之外，我们检测到缺乏PcsB的细胞的整体基因表达谱几乎没有变化。因此，我们的数据表明，LysM结构域蛋白部分补偿了PcsB功能的缺失，并允许肺炎球菌存活和缓慢生长。
The streptococcal protein required for cell separation B (PcsB) is predicted to play an important role in peptidoglycan metabolism, based on sequence motifs and altered phenotypes of gene deletion mutant cells exhibiting defects in cell separation. However, no enzymic activity has been demonstrated for PcsB so far. By generating gene deletion mutant strains in four different genetic backgrounds we could demonstrate that pcsB is not essential for cell survival in Streptococcus pneumoniae, but is essential for proper cell division. Deletion mutant cells displayed cluster formation due to aberrant cell division, reduced growth and antibiotic sensitivity that were fully reverted by transformation with a plasmid carrying pcsB. Immunofluorescence staining revealed that PcsB was localized to the cell poles, similarly to PBP3 and LytB, enzymes with demonstrated peptidoglycan-degrading activity required for daughter cell separation. Similarly to other studies with PcsB homologues, we could not detect peptidoglycan-lytic activity with recombinant or native pneumococcal PcsB in vitro. In addition to defects in septum placement and separation, the absence of PcsB induced an increased release of several proteins, such as enolase, MaIX and the SP0107 LysM domain protein. Interestingly, genes encoding both LysM domain-containing proteins that are present in the pneumococcal genome (SP0107 and SP2063) and predicted to be involved in cell wall metabolism were found to be highly overexpressed (14-33-fold increase) in Delta pcsB cells in two different genetic backgrounds. Otherwise, we detected very few changes in the global gene expression profile of cells lacking PcsB. Thus our data suggest that LysM domain proteins partially compensate for the lack of PcsB function and allow the survival and slow growth of the pneumococcus.