MACCHESS CONSORTIUM FOR PHASING METHODS IN MACROMOLECULAR CRYSTALLOGRAPHY

金属酶一氧化氮合酶(NOS)调节一氧化氮 氧化物(NO)的合成及其生物活性。NO有一个 双重角色：1)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)用于防御的细胞毒剂 抗肿瘤细胞和细胞内寄生虫。发现一氧化氮合酶 诱导型(INOS)、结构性内皮(ENOS)和结构性 神经元(NNOS)亚型具有重要的生物学功能 通过采用耐人寻味的钙调节机制和 结合了五个辅因子的独特组合：血红素， 加氧酶结构域中的四氢生物蝶呤和FMN、FAD 和NADPH包含在还原酶域中。我们已经得到了晶体 小鼠诱导型一氧化氮合酶结构域的衍射角为2.5埃 用同步加速器源在100K下分辨半胱氨酸突变体 INOSox，旨在促进衍生化，正在生产和 其中一个已经被结晶了。INOSox的原子结构 应该会对理解一种独特的催化剂有很大的帮助 一氧化氮合酶和一氧化氮的作用机制及其潜在的生理作用。

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.