Cobalamin decyanation by the membrane transporter BtuM

IF 4.4 2区生物学 Q2 BIOCHEMISTRY & MOLECULAR BIOLOGY Structure Pub Date : 2024-05-10 DOI:10.1016/j.str.2024.04.014

Jose M. Martínez Felices, Yan Borges Barreto, Chancievan Thangaratnarajah, Jacob J. Whittaker, Adriano M. Alencar, Albert Guskov, Dirk J. Slotboom

引用次数: 0

Abstract

BtuM is a bacterial cobalamin transporter that binds the transported substrate in the base-off state, with a cysteine residue providing the α-axial coordination of the central cobalt ion via a sulfur-cobalt bond. Binding leads to decyanation of cobalamin variants with a cyano group as the β-axial ligand. Here, we report the crystal structures of untagged BtuM bound to two variants of cobalamin, hydroxycobalamin and cyanocobalamin, and unveil the native residue responsible for the β-axial coordination, His28. This coordination had previously been obscured by non-native histidines of His-tagged BtuM. A model in which BtuM initially binds cobinamide reversibly with low affinity (K_D = 4.0 μM), followed by the formation of a covalent bond (rate constant of 0.163 s⁻¹), fits the kinetics data of substrate binding and decyanation of the cobalamin precursor cobinamide by BtuM. The covalent binding mode suggests a mechanism not used by any other transport protein.

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膜转运体 BtuM 的钴胺素脱氰作用

BtuM 是一种细菌钴胺素转运体，它在基态下与转运的底物结合，半胱氨酸残基通过硫-钴键为中心钴离子提供 α 轴配位。结合会导致以氰基为 β 轴配体的钴胺素变体发生脱氰作用。在这里，我们报告了未标记的 BtuM 与两种钴胺素变体（羟基钴胺素和氰基钴胺素）结合的晶体结构，并揭示了负责 β 轴配位的本机残基 His28。这种配位以前曾被 His 标记的 BtuM 的非原生组氨酸所掩盖。BtuM 最初以低亲和力（KD = 4.0 μM）可逆地结合钴酰胺，随后形成共价键（速率常数为 0.163 s-1），这一模型符合 BtuM 结合底物和脱钴胺前体钴酰胺的动力学数据。共价结合模式表明这是一种其他任何转运蛋白都没有采用的机制。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Structure 生物-生化与分子生物学

CiteScore

8.90

自引率

1.80%

发文量

155

审稿时长

3-8 weeks

期刊介绍： Structure aims to publish papers of exceptional interest in the field of structural biology. The journal strives to be essential reading for structural biologists, as well as biologists and biochemists that are interested in macromolecular structure and function. Structure strongly encourages the submission of manuscripts that present structural and molecular insights into biological function and mechanism. Other reports that address fundamental questions in structural biology, such as structure-based examinations of protein evolution, folding, and/or design, will also be considered. We will consider the application of any method, experimental or computational, at high or low resolution, to conduct structural investigations, as long as the method is appropriate for the biological, functional, and mechanistic question(s) being addressed. Likewise, reports describing single-molecule analysis of biological mechanisms are welcome. In general, the editors encourage submission of experimental structural studies that are enriched by an analysis of structure-activity relationships and will not consider studies that solely report structural information unless the structure or analysis is of exceptional and broad interest. Studies reporting only homology models, de novo models, or molecular dynamics simulations are also discouraged unless the models are informed by or validated by novel experimental data; rationalization of a large body of existing experimental evidence and making testable predictions based on a model or simulation is often not considered sufficient.