A genomic signature for endosporulation includes a gene coding for a protease, YabG, which in the model organism Bacillus subtilis is involved in assembly of the spore coat. We show that in the human pathogen Clostridioidesm difficile, YabG is critical for the assembly of the coat and exosporium layers of spores. YabG is produced during sporulation under the control of the mother cell-specific regulators σE and σK and associates with the spore surface layers. YabG shows an N-terminal SH3-like domain and a C-terminal domain that resembles single domain response regulators, such as CheY, yet is atypical in that the conserved phosphoryl-acceptor residue is absent. Instead, the CheY-like domain carries residues required for activity, including Cys207 and His161, the homologues of which form a catalytic diad in the B. subtilis protein, and also Asp162. The substitution of any of these residues by Ala, eliminates an auto-proteolytic activity as well as interdomain processing of CspBA, a reaction that releases the CspB protease, required for proper spore germination. An in-frame deletion of yabG or an allele coding for an inactive protein, yabGC207A, both cause misassemby of the coat and exosporium and the formation of spores that are more permeable to lysozyme and impaired in germination and host colonization. Furthermore, we show that YabG is required for the expression of at least two σK-dependent genes, cotA, coding for a coat protein, and cdeM, coding for a key determinant of exosporium assembly. Thus, YabG also impinges upon the genetic program of the mother cell possibly by eliminating a transcriptional repressor. Although this activity has not been described for the B. subtilis protein and most of the YabG substrates vary among sporeformers, the general role of the protease in the assembly of the spore surface is likely to be conserved across evolutionary distance.

中文翻译：

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艰难梭菌中孢子表面层的组装、萌发和宿主定殖需要孢子形成特征蛋白酶。

内孢子形成的基因组特征包括编码蛋白酶YabG的基因，该酶在模型生物枯草芽孢杆菌中参与孢子外壳的组装。我们发现，在人类病原体艰难梭菌中，YabG 对于孢子外壳层和孢子外层的组装至关重要。YabG 在母细胞特异性调节因子 σE 和 σK 的控制下在孢子形成过程中产生，并与孢子表面层相关。YabG 显示 N 端 SH3 样结构域和 C 端结构域，类似于单结构域响应调节因子（例如 CheY），但不典型，因为不存在保守的磷酰基受体残基。相反，CheY 样结构域携带活性所需的残基，包括 Cys207 和 His161（其同源物在枯草芽孢杆菌蛋白中形成催化二联体）以及 Asp162。这些残基中的任何一个被 Ala 取代，消除了 CspBA 的自蛋白水解活性以及域间加工，这是一种释放正确孢子萌发所需的 CspB 蛋白酶的反应。yabG 或编码无活性蛋白 yabGC207A 的等位基因的框内缺失都会导致外壳和孢子外膜的错误组装，以及形成更容易渗透溶菌酶并损害萌发和宿主定植的孢子。此外，我们发现 YabG 是至少两个 σK 依赖基因的表达所必需的，cotA 编码外壳蛋白，cdeM 编码外孢子组装的关键决定因素。因此，YabG 还可能通过消除转录阻遏物来影响母细胞的遗传程序。尽管尚未描述枯草芽孢杆菌蛋白的这种活性，并且大多数 YabG 底物在孢子形成体之间有所不同，但蛋白酶在孢子表面组装中的一般作用可能在整个进化距离中保持保守。