MACCHESS CONSORTIUM FOR PHASING METHODS IN MACROMOLECULAR CRYSTALLOGRAPHY

金属酶一氧化氮合酶（NOS）调节一氧化氮的合成， 氧化物（NO）的合成，从而其生物活性。 没有一个 双重角色：1）一种可扩散的生物信使， 神经传递，长时程增强，血小板聚集， 和血压调节，以及2）用于防御的细胞毒性剂 对抗肿瘤细胞和细胞内寄生虫。 NOS酶，发现 诱导型（iNOS）、组成型内皮细胞（eNOS）和组成型内皮细胞（eNOS） 神经元型一氧化氮合酶（nNOS）亚型发挥着重要的生物学功能 通过采用一种有趣的钙调节机制， 结合了五个辅因子的独特组合：血红素， 四氢生物蝶呤，包含在加氧酶结构域中，以及FMN、FAD 和包含在还原酶结构域中的NADPH。 我们得到了晶体 小鼠iNOS加氧酶结构域， 分辨率与同步辐射源在100 K。半胱氨酸突变体 正在生产旨在促进衍生化的iNOSox， 其中一个已经结晶了。 iNOSox的原子结构 应该能为理解一种独特的催化剂提供更多的见解， 机制和潜在的生理作用的NOS和NO。

The metalloenzyme nitric oxide synthase (NOS) regulates nitric oxide (NO) synthesis and thereby its biological activity. NO has a dual role as 1) a diffusible, biological messenger for neurotransimission, long-term potentiatltion, platelet aggregation, and blood pressure regulation and 2) a cytotoxic agent for defense against tumor cells and intracellulare parasites. NOS enzymes, found in inducible (iNOS), constitutive endothelial (eNOS), and constitutive neuronal (nNOS) isoforms acheive their important biological function by adopting an intriguing calcium-regulated mechanism and incorporating a unique assembly of five cofactors: heme, tetrahydrobiopterin, contained in an oxygenase domain, and FMN, FAD and NADPH contained in a reductase domain. We have obtained crystals of the murine iNOS oxygenase domain that diffract to 2.5 angstrom resolution with a synchrotron source at 100 K. Cysteine mutants of iNOSox, designed to facilitate derivatization, are being produced and one has already been crystallized. An atomic structure of iNOSox should lend much insight to the understanding of a unique catalytic mechanism and potentially the physiological role of NOS and NO.