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

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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.