Structure and function of novel quinol dehydrogenases involved in bacterial electron transport of nitrate and nitrous oxide respiration

背景技术：各种原核生物能够在异化代谢途径如硝酸盐氨化或反硝化中还原氮氧阴离子如硝酸盐和亚硝酸盐。这些无氧呼吸模式代表了氮素地球化学循环中的重要反应。所涉及的末端还原酶是膜结合或周质金属蛋白（或蛋白质复合物），其定期与膜醌/醌醇池交换电子。有关醌反应酶及其相关电子传递蛋白的结构和功能的知识是有限的。目的：本项目旨在通过研究模式生物Wolinella succinogenes的呼吸Nap和Nos系统，阐明细菌周质硝酸盐和N2 O呼吸完整电子传递链的组成和功能。该项目的主要目标是最近确定的NapGH型膜结合甲基喹啉脱氢酶复合物的结构和功能特性。虽然这个醌醇脱氢酶家族的成员广泛存在于细菌厌氧电子传递系统中，但无论是NapGH型复合物还是其单个亚基都没有被纯化或生化研究。影响：由病原菌如弯曲杆菌属、埃希氏菌属和沙门氏菌属产生的NapGH型复合物被认为是致病因子和有希望的药物靶标，因为它们在宿主入侵和定殖期间在微氧或缺氧条件下的存活中起作用。此外，W.succinogenes细胞通过N2 O呼吸生长的不寻常的能力提供了一个极好的模型系统，用于通过硝酸盐氨化生物将最有效的温室气体N2 O微生物转化为无害的N2。

BACKGROUND: Various prokaryotes are capable to reduce nitrogen oxyanions like nitrate and nitrite in dissimilatory metabolic pathways such as nitrate ammonification ordenitrification. These modes of anaerobic respiration represent important reactions in the biogeochemical nitrogen cycle. The involved terminal reductases are membrane-bound or periplasmic metalloproteins (or protein complexes) that regularly exchange electrons with the membranous quinone/quinol pool. Knowledge on the structure and function of the involved quinone-reactive enzymes and their associated electron transport proteins is limited. GOALS: This project aims to elucidate the composition and function of complete electron transport chains of bacterial periplasmic nitrate and N2O respiration by studying the respective respiratory Nap and Nos systems of the model organism Wolinella succinogenes. The main objective of the project is the structural and functional characterization of membrane-bound menaquinol dehydrogenase complexes of the recently identified NapGH-type. Although members of this quinol dehydrogenase family are widespread in bacterial anaerobic electron transport systems, neither a NapGH-type complex nor its individual subunits have ever been purified or biochemically investigated. IMPACT: NapGH-type complexes produced by pathogenic bacteria like Campylobacter, Escherichia and Salmonella species are regarded as pathogenicity factors and promising pharmaceutical targets due to their role in survival under microaerobic or anoxic conditions during host invasion and colonization. Furthermore, the unusual capacity of W.succinogenes cells to grow by N2O respiration provides an excellent model system for the microbial conversion of the most potent greenhouse gas N2O to harmless N2 by a nitrate ammonifying organism.