Alexei Andrea G, Bullen Nathan P, Garrett Stephen R, Sychantha David, Whitney John C
Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada; Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada; Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
J Biol Chem. 2024 Dec;300(12):108007. doi: 10.1016/j.jbc.2024.108007. Epub 2024 Nov 16.
The human gastrointestinal tract is a competitive environment inhabited by dense polymicrobial communities. Bacteroides, a genus of Gram-negative anaerobes, are prominent members of this ecological niche. Bacteroides spp. uses a repertoire of mechanisms to compete for resources within this environment such as the delivery of proteinaceous toxins into neighbouring competitor bacteria and the ability to consume unique metabolites available in the gut. In recent work, Bacteroides stercoris gut colonization was linked to the activity of a prophage-encoded ADP-ribosyltransferase, which was found to stimulate the release of the metabolite inosine from host epithelial cells. This fitness factor, termed Bxa, shares a similar genomic arrangement to bacterial toxins encoded within interbacterial antagonism loci. Here, we report that Bxa also possesses antibacterial ADP-ribosyltransferase activity, raising the question of how Bxa-producing bacteria resist intoxication prior to Bxa's release from cells. To this end, we identify two cognate immunity proteins, Bsi and BAH, that neutralize Bxa's antibacterial activity using distinct mechanisms. BAH acts as an enzymatic immunity protein that reverses Bxa ADP-ribosylation whereas Bsi physically interacts with Bxa and blocks its ADP-ribosylation activity. We also find that the N-terminal domain of Bxa is dispensable for toxicity and homologous domains in other bacteria are fused to a diverse array of predicted toxins found throughout the Bacteroidaceae, suggesting that Bxa belongs to a broader prophage encoded polymorphic toxin system. Overall, this work shows that Bxa is a promiscuous ADP-ribosyltransferase and that B. stercoris possesses mechanisms to protect itself from the toxic activity of this prophage encoded fitness factor.
人类胃肠道是一个由密集的多微生物群落栖息的竞争环境。拟杆菌属，革兰氏阴性厌氧菌的一个属，是这个生态位的重要成员。拟杆菌属利用一系列机制在这个环境中竞争资源，例如将蛋白质毒素传递到邻近的竞争细菌中，以及消耗肠道中可用的独特代谢物的能力。在最近的工作中，硬结拟杆菌的肠道定殖与一种原噬菌体编码的ADP-核糖基转移酶的活性有关，该酶被发现能刺激宿主上皮细胞释放代谢物肌苷。这种适应性因子，称为Bxa，与细菌间拮抗位点内编码的细菌毒素具有相似的基因组排列。在这里，我们报告Bxa也具有抗菌ADP-核糖基转移酶活性，这就提出了一个问题，即产生Bxa的细菌在Bxa从细胞中释放之前如何抵抗中毒。为此，我们鉴定了两种同源免疫蛋白，Bsi和BAH，它们使用不同的机制中和Bxa的抗菌活性。BAH作为一种酶促免疫蛋白，可逆转Bxa的ADP-核糖基化，而Bsi与Bxa发生物理相互作用并阻断其ADP-核糖基化活性。我们还发现，Bxa的N端结构域对于毒性是可有可无的，并且其他细菌中的同源结构域与在拟杆菌科中发现的各种预测毒素融合，这表明Bxa属于更广泛的原噬菌体编码的多态毒素系统。总的来说，这项工作表明Bxa是一种混杂的ADP-核糖基转移酶，并且硬结拟杆菌具有保护自身免受这种原噬菌体编码的适应性因子毒性活性影响的机制。
