Cytochrome (cyt) P460 is a c-type monoheme enzyme found in ammonia-oxidizing bacteria (AOB) and methanotrophs; additionally, genes encoding it have been found in some pathogenic bacteria. Cyt P460 is defined by a unique post-translational modification to the heme macrocycle, where a lysine (Lys) residue covalently attaches to the 13′ meso carbon of the porphyrin, modifying this heme macrocycle into the enzyme’s eponymous P460 cofactor, similar to the cofactor found in the enzyme hydroxylamine oxidoreductase. This cross-link imbues the protein with unique spectroscopic properties, the most obvious of which is the enzyme’s green color in solution. Cyt P460 from the AOB Nitrosomonas europaea is a homodimeric redox enzyme that produces nitrous oxide (N₂O) from 2 equiv of hydroxylamine. Mutation of the Lys cross-link results in spectroscopic features that are more similar to those of standard cyt c′ proteins and renders the enzyme catalytically incompetent for NH₂OH oxidation. Recently, the necessity of a second-sphere glutamate (Glu) residue for redox catalysis was established; it plausibly serves as proton relay during the first oxidative half of the catalytic cycle. Herein, we report the first crystal structure of a cross-link deficient cyt P460. This structure shows that the positioning of the catalytically essential Glu changes by approximately 0.8 Å when compared to a cross-linked, catalytically competent cyt P460. It appears that the heme–Lys cross-link affects the relative position of the P460 cofactor with respect to the second-sphere Glu residue, therefore dictating the catalytic competency of the enzyme.

中文翻译：

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细胞色素P460中的Heme-Lys交联通过增强二级配位域体系结构来促进催化作用。

细胞色素（cyt）P460是在氨氧化细菌（AOB）和甲烷营养菌中发现的c型单血红素酶；另外，已经在一些病原细菌中发现了编码它的基因。Cyt P460通过对血红素大环的独特翻译后修饰来定义，其中赖氨酸（Lys）残基共价附于卟啉的13'内消旋碳，从而将该血红素大环修饰为酶的同义P460辅因子，类似于辅因子在羟胺氧化还原酶中发现。这种交联使蛋白质具有独特的光谱特性，其中最明显的是溶液中酶的绿色。来自AOB亚硝基亚油菜的Cyt P460是一种同二聚体氧化还原酶，可产生一氧化二氮（N₂ O）的羟胺。Lys交联的突变导致光谱特征与标准cyt c '蛋白的光谱特征更加相似，并使酶对NH _2的催化能力不足OH氧化。最近，已经确定了第二球谷氨酸（Glu）残留物用于氧化还原催化的必要性。它可能在催化循环的第一半氧化阶段充当质子传递。在此，我们报告了一种交联缺陷型cyt P460的第一晶体结构。这种结构表明，与交联的，具有催化活性的Cyt P460相比，具有催化作用的Glu的定位变化了约0.8Å。看来血红素-Lys交联会影响P460辅因子相对于第二个球体Glu残基的相对位置，因此决定了酶的催化能力。