[Fe]‐hydrogenase (Hmd) catalyzes the reversible hydrogenation of methenyltetrahydromethanopterin (methenyl‐H₄MPT⁺) with H₂. Hmd contains the iron–guanylylpyridinol (FeGP) cofactor, which is sensitive to light and oxidative stress. A natural protection mechanism is reported for Hmd based on structural and biophysical data. Hmd from Methanothermobacter marburgensis (mHmd) was found in a hexameric state, where an expanded oligomerization loop is detached from the dimer core and intrudes into the active site of a neighboring dimer. An aspartic acid residue from the loop ligates to Fe^II of the FeGP cofactor and thus blocks the postulated H₂‐binding site. In solution, this enzyme is in a hexamer‐to‐dimer equilibrium. Lower enzyme concentrations, and the presence of methenyl‐H₄MPT⁺, shift the equilibrium toward the active dimer side. At higher enzyme concentrations—as present in the cell—the enzyme is predominantly in the inactive hexameric state and is thereby protected against light and oxidative stress.

中文翻译：

---

甲烷甲烷热菌的[Fe]-加氢酶如何保护免受光和氧化胁迫

[Fe]-氢化酶（Hmd）催化H ₂催化亚甲基四氢甲基蝶呤（methenyl-H ₄ MPT ⁺）的可逆氢化。Hmd含有铁-鸟苷基吡啶（FeGP）辅因子，它对光和氧化应激敏感。据报道，基于结构和生物物理数据，Hmd具有天然保护机制。发现来自马氏甲烷嗜热杆菌的Hmd（mHmd）为六聚体状态，其中扩展的低聚环与二聚体核心分离，并侵入相邻的二聚体的活性位点。来自环的天冬氨酸残基与FeGP辅因子的Fe ^II连接，从而阻断假定的H _2。-结合位点。在溶液中，该酶处于六聚体到二聚体的平衡状态。较低的酶浓度和亚甲基H ₄ MPT ⁺的存在将平衡移向活性二聚体侧。在细胞中存在较高的酶浓度时，该酶主要处于非活性六聚体状态，因此可以免受光和氧化应激的影响。