Due to their adjacent location in the genomes of Desulfovibrio species and their potential for formation of an electron transfer pathway in sulfate-reducing prokaryotes, adenosyl phosphosulfate (APS) reductase (Apr) and quinone-interacting membrane-bound oxidoreductase (Qmo) have been thought to interact together during the reduction of APS. This interaction was recently verified in Desulfovibrio desulfuricans. Membrane proteins of Desulfovibrio vulgaris Hildenborough DqmoABCD JW9021, a deletion mutant, were compared to the parent strain using blue-native PAGE to determine whether Qmo formed a complex with Apr or other proteins. In the parent strain of D. vulgaris, a unique band was observed that contained all four Qmo subunits, and another band contained three subunits of Qmo, as well as subunits of AprA and AprB. Similar results were observed with bands excised from membrane preparations of Desulfovibrio alaskensis strain G20. These results are in support of the formation of a physical complex between the two proteins; a result that was further confirmed by the co-purification of QmoA/B and AprA/B from affinity-tagged D. vulgaris Hildenborough strains (AprA, QmoA and QmoB) regardless of which subunit had been tagged. This provides clear evidence for the presence of a Qmo-Apr complex that is at least partially stable in protein extracts of D. vulgaris and D. alaskensis.
INTRODUCTIONSulfate-reducing prokaryotes (SRPs) respire sulphate, and although their entire respiratory process has not been fully elucidated, there has been much progress in determining the role of a number of SRP proteins (Pereira et al., 2007). Current concepts for sulfate respiration involve a range of both intrinsic membrane proteins, as well as soluble cytoplasmic and periplasmic proteins, some of which are required exclusively for H 2 or formate oxidation (Li et al., 2009). The first step in the SRP respiration process involves the reduction of sulfate to sulfite, a two electron reduction. In order for this step to proceed, sulfate must first be converted to adenosyl phosphosulfate (APS) through a reaction involving ATP being carried out by the enzyme, sulfate adenylyltransferase (Sat) (Pereira et al., 2007), which is present in all SRPs (Meyer & Kuever, 2007a). APS reductase (Apr) then catalyses the reduction of APS to sulfite and adenosine monophosphate (Lampreia et al., 1994). The Apr (AprBA) has been purified as a soluble Abbreviations: Apr, adenosyl phosphosulfate reductase; APS, adenosyl phosphosulfate; DDM, dodecyl maltoside; Qmo, quinone-interacting membrane-bound oxidoreductase; Sat, sulfate adenylyltransferase; SRP, sulfate-reducing prokaryote.Supplementary material is available with the online version of this paper. complex with a molecular mass of about 95 kDa and is thought to be arranged in a 1 : 1 a-b heterodimer (Fritz et al., 2000). The a subunit is the catalytic subunit with the FAD-binding region, whereas the b subunit contains a ferredoxin domain that is involved in electron transfer (Fritz et al., 2002).Because of the...