MSU-DOE Plant Research Laboratory, Michigan State University, East Lansing, MI 48824.
Environmental Genomics and Systems Biology Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720.
Proc Natl Acad Sci U S A. 2024 Dec 3;121(49):e2414220121. doi: 10.1073/pnas.2414220121. Epub 2024 Nov 25.
Bacterial microcompartments (BMCs) are prokaryotic organelles that consist of a protein shell which sequesters metabolic reactions in its interior. While most of the substrates and products are relatively small and can permeate the shell, many of the encapsulated enzymes require cofactors that must be regenerated inside. We have analyzed the occurrence of an enzyme previously assigned as a cobalamin (vitamin B) reductase and, curiously, found it in many unrelated BMC types that do not employ B cofactors. We propose Nicotinamide adenine dinucleotide (NAD+) regeneration as the function of this enzyme and name it Metabolosome Nicotinamide Adenine Dinucleotide Hydrogen (NADH) dehydrogenase (MNdh). Its partner shell protein BMC-T (tandem domain BMC shell protein of the single layer type for electron transfer) assists in passing the generated electrons to the outside. We support this hypothesis with bioinformatic analysis, functional assays, Electron Paramagnetic Resonance spectroscopy, protein voltammetry, and structural modeling verified with X-ray footprinting. This finding represents a paradigm for the BMC field, identifying a new, widely occurring route for cofactor recycling and a new function for the shell as separating redox environments.
细菌微隔间（BMC）是由蛋白质外壳组成的原核细胞器，将代谢反应隔离在其内部。虽然大多数底物和产物相对较小，可以渗透外壳，但许多被包裹的酶需要在内部再生辅助因子。我们分析了一种先前被指定为钴胺素（维生素 B）还原酶的酶的出现情况，令人好奇的是，我们在许多不使用 B 辅助因子的不相关 BMC 类型中发现了它。我们提出 NAD+再生是该酶的功能，并将其命名为 Metabolosome Nicotinamide Adenine Dinucleotide Hydrogen (NADH) dehydrogenase (MNdh)。其伴侣外壳蛋白 BMC-T（单层类型的串联域 BMC 外壳蛋白，用于电子传递）有助于将生成的电子传递到外部。我们通过生物信息学分析、功能测定、电子顺磁共振波谱学、蛋白质伏安法和 X 射线足迹结构建模来支持这一假设。这一发现代表了 BMC 领域的一个范例，确定了一种新的、广泛存在的辅助因子回收途径，以及外壳作为分离氧化还原环境的新功能。
