Pneumococcal CbpD is a murein hydrolase that requires a dual cell envelope binding specificity to kill target cells during fratricide
Pneumococcal CbpD is a murein hydrolase that requires a dual cell envelope binding specificity to kill target cells during fratricide
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DOI：
10.1111/j.1365-2958.2010.07143.x
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发表时间：
2010-05-01
影响因子：
3.6
通讯作者：
Havarstein, Leiv Sigve
中科院分区：
文献类型：
--
作者：
Eldholm, Vegard;Johnsborg, Ola;Havarstein, Leiv Sigve
具有自然遗传转化能力的肺炎球菌表达了一些参与DNA结合、摄取、易位和重组的蛋白质。此外，它们攻击和溶解存在于相同环境中的无能力的姐妹细胞。这种现象被称为杀兄弟。肺炎球菌杀兄弟体的关键效应因子是CbpD，这是一种分泌蛋白，包含一个n端CHAP结构域、两个SH3b结构域和一个c端胆碱结合结构域（CBD）。CbpD被认为可以降解靶细胞的细胞壁，但缺乏支持这一假设的实验证据。在这里，我们发现CbpD确实具有水解活性，并且这种活性需要功能性CBD和SH3b结构域。为了更好地了解CbpD的非催化c端区域所起的关键作用，在CBD和SH3b结构域与绿色荧光蛋白（GFP）之间构建了多种翻译融合。结果表明，SH3b结构域特异性识别和结合肽聚糖，而CBD结构域作为定位信号，将CbpD引导到肺炎球菌细胞的隔膜区。有趣的是，透射电镜分析显示，CbpD攻击的靶细胞在间隔区破裂，与CBD结构域显示的结合特异性一致。
P>Pneumococci that are competent for natural genetic transformation express a number of proteins involved in binding, uptake, translocation and recombination of DNA. In addition, they attack and lyse non-competent sister cells present in the same environment. This phenomenon has been termed fratricide. The key effector of pneumococcal fratricide is CbpD, a secreted protein encompassing an N-terminal CHAP domain, two SH3b domains and a C-terminal choline-binding domain (CBD). CbpD is believed to degrade the cell wall of target cells, but experimental evidence supporting this hypothesis has been lacking. Here, we show that CbpD indeed has muralytic activity, and that this activity requires functional CBD and SH3b domains. To better understand the critical role played by the non-catalytic C-terminal region of CbpD, various translational fusions were constructed between the CBD and SH3b domains and green fluorescent protein (GFP). The results showed that the SH3b domains specifically recognize and bind peptidoglycan, while the CBD domain functions as a localization signal that directs CbpD to the septal region of the pneumococcal cell. Intriguingly, transmission electron microscopy analysis revealed that target cells attacked by CbpD ruptures at the septal region, in accordance with the binding specificity displayed by the CBD domain.