Center for Advanced Microbial Processing, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA.
Institute for Molecular Medicine and Infectious Disease, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA.
J Bacteriol. 2021 Jul 8;203(15):e0017221. doi: 10.1128/JB.00172-21.
Vitamin B belongs to a family of structurally diverse cofactors with over a dozen natural analogs, collectively referred to as cobamides. Most bacteria encode cobamide-dependent enzymes, many of which can only utilize a subset of cobamide analogs. Some bacteria employ a mechanism called cobamide remodeling, a process in which cobamides are converted into other analogs to ensure that compatible cobamides are available in the cell. Here, we characterize an additional pathway for cobamide remodeling that is distinct from the previously characterized ones. Cobamide synthase (CobS) is an enzyme required for cobamide biosynthesis that attaches the lower ligand moiety in which the base varies between analogs. In a heterologous model system, we previously showed that Vibrio cholerae CobS (VcCobS) unexpectedly conferred remodeling activity in addition to performing the known cobamide biosynthesis reaction. Here, we show that additional species perform the same remodeling reaction, and we further characterize VcCobS-mediated remodeling using bacterial genetics and assays. We demonstrate that VcCobS acts upon the cobamide pseudocobalamin directly to remodel it, a mechanism which differs from the known remodeling pathways in which cobamides are first cleaved into biosynthetic intermediates. This suggests that some CobS homologs have the additional function of cobamide remodeling, and we propose the term "direct remodeling" for this process. This characterization of yet another pathway for remodeling suggests that cobamide profiles are highly dynamic in polymicrobial environments, with remodeling pathways conferring a competitive advantage. Cobamides are widespread cofactors that mediate metabolic interactions in complex microbial communities. Few studies directly examine cobamide profiles, but several have shown that mammalian gastrointestinal tracts are rich in cobamide analogs. Studies of intestinal bacteria, including beneficial commensals and pathogens, show variation in the ability to produce and utilize different cobamides. Some bacteria can convert imported cobamides into compatible analogs in a process called remodeling. Recent discoveries of additional cobamide remodeling pathways, including this work, suggest that remodeling is an important factor in cobamide dynamics. Characterization of such pathways is critical in understanding cobamide flux and nutrient cross-feeding in polymicrobial communities, and it facilitates the establishment of microbiome manipulation strategies via modulation of cobamide profiles.
维生素 B 属于具有十多种天然类似物的结构多样的辅酶家族，统称为 cobamides。大多数细菌编码 cobamide 依赖性酶，其中许多酶只能利用 cobamide 类似物的一部分。一些细菌采用一种称为 cobamide 重塑的机制，该过程中 cobamides 被转化为其他类似物，以确保细胞中存在兼容的 cobamides。在这里，我们描述了一种不同于先前描述的 cobamide 重塑途径。 cobamide 合酶（CobS）是 cobamide 生物合成所需的酶，它连接碱基在类似物之间变化的下配体部分。在异源模型系统中，我们之前表明，霍乱弧菌 CobS（VcCobS）除了执行已知的 cobamide 生物合成反应外，出乎意料地赋予了重塑活性。在这里，我们表明其他 种执行相同的重塑反应，并且我们使用细菌遗传学和 测定进一步表征了 VcCobS 介导的重塑。我们证明 VcCobS 直接作用于 cobamide 假钴胺素来重塑它，这种机制不同于 cobamides 首先被切割成生物合成中间体的已知重塑途径。这表明一些 CobS 同源物具有 cobamide 重塑的额外功能，我们将该过程称为“直接重塑”。这种对重塑的另一种途径的描述表明，在多微生物环境中 cobamide 谱高度动态，重塑途径赋予竞争优势。 cobamides 是广泛存在的辅酶，介导复杂微生物群落中的代谢相互作用。很少有研究直接检查 cobamide 谱，但有几项研究表明哺乳动物胃肠道富含 cobamide 类似物。对肠道细菌的研究，包括有益的共生菌和病原体，显示出产生和利用不同 cobamides 的能力的变化。一些细菌可以将进口的 cobamides 转化为兼容的类似物，这一过程称为重塑。包括这项工作在内的新发现的额外 cobamide 重塑途径表明，重塑是 cobamide 动态的一个重要因素。对这种途径的特征分析对于理解多微生物群落中的 cobamide 通量和营养交叉喂养至关重要，并通过调节 cobamide 谱促进微生物组操纵策略的建立。
