Biochemistry. 2024 Aug 6;63(15):1955-1962. doi: 10.1021/acs.biochem.4c00216. Epub 2024 Jul 16.
In mammals, cobalamin is an essential cofactor that is delivered by a multitude of chaperones in an elaborate trafficking pathway to two client enzymes, methionine synthase and methylmalonyl-CoA mutase (MMUT). Rhodibalamins, the rhodium analogs of cobalamins, have been described as antimetabolites due to their ability to inhibit bacterial growth. In this study, we have examined the reactivity of adenosylrhodibalamin (AdoRhbl) with two key human chaperones, MMACHC (also known as CblC) and adenosyltransferase (MMAB, also known as ATR), and with the human and MMUT. We demonstrate that while AdoRhbl binds tightly to all four proteins, the Rh-carbon bond is resistant to homolytic (on MMAB and MMUT) as well as heterolytic (on MMACHC) rupture. On the other hand, MMAB catalyzes Rh-carbon bond formation, converting rhodi(I)balamin in the presence of ATP to AdoRhbl. We report the first crystal structure of a rhodibalamin (AdoRhbl) bound to a B protein, i.e., MMAB, in the presence of triphosphate, which shows a weakened but intact Rh-carbon bond. The structure provides insights into how MMAB cleaves the corresponding Co-carbon bond in a sacrificial homolytic reaction that purportedly functions as a cofactor sequestration strategy. Collectively, the study demonstrates that while the noble metal substitution of cobalt by rhodium sets up structural mimicry, it compromises chemistry, which could be exploited for targeting human and bacterial B chaperones and enzymes.
在哺乳动物中，钴胺素是一种必需的辅因子，通过一系列复杂的伴侣蛋白在复杂的运输途径中传递给两种客户酶，即蛋氨酸合酶和甲基丙二酰辅酶 A 变位酶（MMUT）。钌钴胺素是钴胺素的钌类似物，由于其抑制细菌生长的能力，被描述为抗代谢物。在这项研究中，我们研究了腺苷基钌钴胺素（AdoRhbl）与两种关键的人类伴侣蛋白，即 MMACHC（也称为 CblC）和腺苷转移酶（MMAB，也称为 ATR），以及人类和 MMUT 的反应性。我们证明，尽管 AdoRhbl 与所有四种蛋白质紧密结合，但 Rh-碳键对均裂（在 MMAB 和 MMUT 上）和异裂（在 MMACHC 上）断裂具有抗性。另一方面，MMAB 催化 Rh-碳键形成，在 ATP 的存在下将 rhodi（I）balamin 转化为 AdoRhbl。我们报告了第一个与 B 蛋白（即 MMAB）结合的 Rh 型钴胺素（AdoRhbl）的晶体结构，该结构存在三磷酸，显示出减弱但完整的 Rh-碳键。该结构提供了关于 MMAB 如何在牺牲性均裂反应中切割相应的 Co-碳键的见解，据称该反应作为一种辅因子隔离策略发挥作用。总的来说，该研究表明，虽然钴的贵金属取代钌建立了结构模拟，但它损害了化学性质，这可能被用于靶向人类和细菌 B 伴侣蛋白和酶。
