Biosynthesis of Amino Acid Derived Quinone Cofactors

描述（由申请人提供）：甲胺脱氢酶（MADH），一种在甲基营养/自养细菌中发现的代谢酶，含有醌辅助因子，色氨酸色氨酸醌（TTQ），源自蛋白质中两个色氨酸残基的翻译后修饰。MADH的成熟涉及至少4种其他蛋白质，我们已经开始表征其中一种蛋白质，MauG。它是一种非常不寻常的二血红素酶，负责完成TTQ的合成。MauG （preMADH）的天然底物是MADH的119 kda蛋白前体，具有部分形成的辅助因子。MauG催化六电子氧化完成TTQ生物合成，使用分子氧或过氧化氢作为第二底物。催化反应涉及一种前所未有的高价二血红素中间体，它异常稳定。此申请是对“NOT-OD-09-058: NIH宣布为竞争性修订申请提供恢复法案基金”的回应。亲本基金（GM066569）的专项目的2是研究MauG与preMADH配合物的晶体结构。这已经达到了2.1¿的分辨率，并且这些晶体可以支持催化周转形成TTQ而不会损失衍射。MauG/preMADH结构揭示了一些没有预料到的特征，这一竞争性修订的目标是建立在这个新的知识平台上。利用定点诱变、x射线晶体学、动力学表征、光谱学和质谱，这种竞争性的修订将使我们能够迅速发现以前未知的高价铁中间体对氧的激活、远距离蛋白质间电子和自由基转移以及氧化修饰蛋白质内特定氨基酸残基的机制。

DESCRIPTION (provided by applicant):Methylamine dehydrogenase (MADH), a metabolic enzyme found in methylotrophic/autotrophic bacteria, contains a quinone cofactor, tryptophan tryptophylquinone (TTQ), derived from the post-translational modification of two Trp residues in the protein. The maturation of MADH involves at least 4 other proteins, and we have begun to characterize one of these proteins, MauG. It is a highly unusual di-heme enzyme responsible for the completion of TTQ synthesis. The natural substrate for MauG (preMADH) is a 119-kDa protein precursor of MADH with a partially formed cofactor. MauG catalyzes a six-electron oxidation to complete TTQ biosynthesis, using either molecular oxygen or hydrogen peroxide as the second substrate. The catalytic reaction involves an unprecedented high-valent di-heme intermediate, which is unusually stable. This application is in response to "NOT-OD-09-058: NIH Announces the Availability of Recovery Act Funds for Competitive Revision Applications." Specific Aim 2 of the parent grant (GM066569) was to solve the crystal structure of MauG in complex with preMADH. This has been achieved to a resolution of 2.1¿, and these crystals can support catalytic turnover to form TTQ without loss of diffraction. The MauG/preMADH structure has revealed features that were not anticipated, and the aims of this competitive revision are built on this new knowledge platform. Using site-directed mutagenesis, X-ray crystallography, kinetic characterization, spectroscopy and mass spectrometry this competitive revision would enable us to rapidly make fundamental discoveries about oxygen activation by a previously unknown high-valent iron intermediate, long range inter-protein electron and radical transfer and mechanisms of oxidative modification to specific amino acid residues within a protein. PUBLIC HEALTH RELEVANCE: MauG is sequentially related to peroxidases that detoxify H2O2 under hypoxic conditions (oxidative stress), but unusually can also activate molecular oxygen, and uses an equivalent catalytic intermediate to human cytochrome P450 enzymes, the major players in drug metabolism, carcinogen activation, biosynthesis of physiologically important molecules, such as steroids, fat-soluble vitamins and fatty acids, as well as the degradation of insecticides and herbicides.