MOLYBDENUM COFACTOR--BIOSYNTHESIS AND FUNCTION

钼辅因子（Moco）存在于四种不同的酶中 催化全球碳的重要转变的家族， 硫和氮循环。 Moco由单核钼 与二硫杂环戊烯基团的硫原子配位，所述二硫杂环戊烯基团是 一种取代的蝶呤衍生物，称为异蝶呤。 酶 在所有三个系统发育王国中都有发现 生命的起源，辅因子的生物合成遵循相同的途径， 在原核生物和真核生物包括植物和人类中。 Moco 缺乏症是作为常染色体隐性遗传性状遗传的，是一种严重的 表现为神经系统异常的人类疾病 导致受影响的个体过早死亡。 实验 本提案概述了莫科的两个重要方面，即 它的生物合成和它的详细功能，一旦它被纳入 转化为目标酶。本提案提出的具体目标 因此，有：（一）莫科早期步骤的特点 通过对酶MoaC的结构研究来进行生物合成。 MOaC最 很可能催化莫科生物合成的第一步， 与磷酸化鸟苷，或第二步，其中A 产生仍然缺少硫原子的异蝶呤前体。 (ii)一种新的蝶呤合成酶的晶体结构分析， 将硫原子结合到一种多巴胺前体中， 多巴胺 异源二聚体蝶呤的小亚基 合成酶含有一个不寻常的C-末端硫代羧酸， 催化过程中的硫供体。 (iii)晶体结构 测定可能作为β-D螯合酶起作用的莫加， 因此，将负责纳入钼，这是目前 在细胞中转化为多巴胺。(iv)高分辨率 含Moco酶二甲基亚砜的结构分析 还原酶，包括不同氧化态的表征和 酶与底物和抑制剂的复合物， 催化机制的详细表征。(v)晶体 生物素亚砜还原酶结构分析 二甲基亚砜还原酶的序列，但底物不同 的特异性 对这两种酶的比较研究将导致更多的 一般了解的作用莫科是发挥酶含有 这个cofactor。

The molybdenum cofactor (Moco) is present in four different enzyme families which catalyze important transformations in the global carbon, sulfur and nitrogen cycles. Moco consists of a mononuclear molybdenum coordinated to the sulfur atoms of a dithiolene group which is part of a substituted pterin derivative termed molybdopterin. Enzymes containing this cofactor are found in all three phylogenetic kingdoms of life, and biosynthesis of the cofactor follows the same pathway, both in prokaryotes and in eukaryotes including plants and human. Moco deficiency is inherited as an autosomal recessive trait and is a severe disease in humans which manifests itself in neurological abnormalities leading to premature death in the affected individuals. The experiments outlined in this proposal address two important aspects of Moco, namely its biosynthesis and its detailed function once it has been incorporated into the target enzymes. The specific aims presented in this proposal therefore are: (i) Characterization of the early steps in Moco biosynthesis through structural studies on the enzyme MoaC. MoaC most likely either catalyzes the first step in Moco biosynthesis starting with a phosphorylated guanosine, or the second step in which A molybdopterin precursor is generated which still lacks the sulfur atoms. (ii) Crystal structure analysis of molybdopterin synthase which incorporates the sulfur atoms into a molybdopterin precursor generating molybdopterin. The small subunit of the heterodimeric molybdopterin synthase contains an unusual C-terminal thiocarboxylate which serves as the sulfur donor during catalysis. (iii) Crystal structure determination of MogA which might function as a molybdochelatase and thus would be responsible for incorporating molybdenum, which is present in the cell as molybdate, into the molybdopterin. (iv) High resolution structure analysis of the Moco-containing enzyme dimethylsulfoxide reductase including characterization of different oxidation states and complexes of the enzyme with substrates and inhibitors which will lead to a detailed characterization of the catalytic mechanism. (v) Crystal structure analysis of biotin sulfoxide reductase, which is related in sequence to dimethylsulfoxide reductase but differs in substrate specificity. Comparative studies of the two enzymes will lead to a more general understanding of the roles Moco is playing in enzymes containing this cofactor.