Abstract
The microaerophilic human parasite Trichomonas vaginalis causes infections in the urogenital tract and is one of the most often sexually transmitted pathogens worldwide. Due to its anaerobic metabolism, it has to quickly remove intracellular oxygen in order to avoid deactivation of essential metabolic enzymes such as oxygen-sensitive pyruvate:ferredoxin oxidoreductase (PFOR). Two major enzyme activities which are responsible for the removal, i.e. reduction, of molecular oxygen have been identified in T. vaginalis flavin reductase, formerly designated NADPH oxidase, which indirectly reduces oxygen to hydrogen peroxide via flavin mononucleotide (FMN), and NADH oxidase which reduces oxygen to water. Flavin reductase has been identified and characterized at the gene level as well as enzymatically, but NADH oxidase has so far only been characterized enzymatically with enzyme isolated from T. vaginalis cell extracts. In this study, we identified NADH oxidase by mass spectrometry after isolation of the enzyme from gel bands positively staining for NADH oxidase activity. In strain C1 (ATCC 30001) which is known to lack NADH oxidase activity completely, the NADH oxidase gene has a deletion at position 1540 of the open reading frame leading to a frame shift and, as a consequence, to premature termination of the encoded polypeptide.
Highlights
The microaerophilic parasite Trichomonas vaginalis is one of the most prevalent sexually transmitted pathogens worldwide, causing hundreds of millions of infections every year (Leitsch, 2016)
Due to its anaerobic metabolism, T. vaginalis has to effectively remove intracellular oxygen in order to prevent the deactivation of essential enzymes such as pyruvate:ferredoxin oxidoreductase
Two major oxygen scavenging activities have been identified which both reside in the cytoplasm (Tanabe 1979; Linstead and Bradley, 1988): NADPH oxidase and NADH oxidase
Summary
The microaerophilic parasite Trichomonas vaginalis is one of the most prevalent sexually transmitted pathogens worldwide, causing hundreds of millions of infections every year (Leitsch, 2016). Two major oxygen scavenging activities have been identified which both reside in the cytoplasm (Tanabe 1979; Linstead and Bradley, 1988): NADPH oxidase and NADH oxidase. The former reduces flavin mononucleotide (FMN) and other flavins through oxidation of NADPH (Linstead and Bradley 1988; Leitsch et al, 2014). Reduced FMN, in turn, rapidly reacts with molecular oxygen to form hydrogen peroxide (Chapman et al, 1999; Leitsch et al, 2014) The latter reduces molecular oxygen to water (Tanabe, 1979) by harnessing electrons derived from NADH. It was described to be monomeric and 98 kDa in size and to be highly vulnerable to atmospheric oxygen
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