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

背景：各种原核生物能够在异化代谢途径中还原硝酸盐和亚硝酸盐等含氮氧阴离子，如硝酸盐氨化和反硝化作用。这些无氧呼吸模式代表了生物地球化学氮循环中的重要反应。所涉及的末端还原酶是膜结合的或周质的金属蛋白(或蛋白复合体)，它们定期与膜上的苯醌/苯二酚池交换电子。对所涉及的苯二酚反应酶及其相关电子传递蛋白的结构和功能的了解有限。目的：本项目旨在通过研究模式生物--琥珀酸狼疮的呼吸Nap和Nos系统，阐明细菌周质硝酸盐和N2O呼吸的完整电子传递链的组成和功能。该项目的主要目标是最近发现的napGH类型的膜结合的Menquinol脱氢酶复合体的结构和功能特征。尽管这种喹酚脱氢酶家族的成员广泛存在于细菌的厌氧电子传递系统中，但无论是napGH型复合体还是它的单个亚基都没有得到纯化或生化研究。影响：由弯曲杆菌、大肠杆菌和沙门氏菌等病原菌产生的NapGH型复合体被认为是致病因子和有前景的药物靶标，因为它们在宿主入侵和定植期间在微氧或缺氧条件下存活的作用。此外，产琥珀酸杆菌细胞通过N2O呼吸生长的不同寻常的能力为硝酸氨化生物将最有效的温室气体N2O微生物转化为无害的氮气提供了一个极好的模式系统。

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.