Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Avenida da República EAN, Oeiras, Portugal.
Texas A&M University, Department of Biology, College Station, Texas, United States of America.
PLoS Pathog. 2023 Nov 13;19(11):e1011741. doi: 10.1371/journal.ppat.1011741. eCollection 2023 Nov.
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.
一个内孢子形成的基因组特征包括一个编码蛋白酶的基因，YabG，在模式生物枯草芽孢杆菌中，它参与孢子衣的组装。我们表明，在人类病原体艰难梭菌中，YabG 对于孢子衣和外孢子层的组装至关重要。YabG 在母细胞特异性调节剂σE 和 σK 的控制下在孢子形成过程中产生，并与孢子表面层结合。YabG 表现出一个 N 端 SH3 样结构域和一个 C 端结构域，类似于单个结构域反应调节剂，如 CheY，但它是非典型的，因为保守的磷酸受体残基不存在。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一个催化二联体，还包括 Asp162。这些残基中的任何一个被 Ala 取代，都会消除自动蛋白水解活性以及 CspBA 的结构域间加工，该反应释放出 CspB 蛋白酶，这对于正确的孢子发芽是必需的。yabG 的无义突变或编码无活性蛋白的等位基因 yabGC207A 的缺失都会导致衣和外孢子的组装错误，形成对溶菌酶更具渗透性且发芽和宿主定殖受损的孢子。此外，我们表明 YabG 是至少两个σK 依赖性基因 cotA（编码衣蛋白）和 cdeM（编码外孢子组装的关键决定因素）表达所必需的。因此，YabG 还可能通过消除转录抑制剂来影响母细胞的遗传程序。虽然这种活性尚未在枯草芽孢杆菌蛋白中描述，并且大多数 YabG 底物在孢子形成体中不同，但蛋白酶在孢子表面组装中的一般作用可能在进化距离上是保守的。
