A Second Terminal Oxidase in Sulfolobus acidocaldarius

Abstract

We previously found that the soxABCD operon encodes a quinol oxidase complex in Sulfolobus acidocaldarius and this enzyme was purified and characterized. In this study, we have used a cloning procedure based on the conservation of oxidase sequences and the polymerase chain reaction to isolate a new gene (soxM) encoding a subunit of another terminal oxidase. This terminal oxidase is a fusion between two central components of cytochrome oxidases, subunits I and III. soxM forms a transcriptional unit which is expressed under heterotrophic growth conditions. The corresponding protein was detected by direct protein sequencing in a preparation enriched with a cytochrome absorbing light at 562 nm. This preparation contains a terminal oxidase which is able to oxidize the artificial substrate N,N,N′,N′ ‐tetramethyl‐p ‐phenylenediamine. This preparation also contains SoxC, a protein homologous to the mitochondrial cytochrome b, and a Rieske iron‐sulphur center. We suggest that SoxM is the core component of a second terminal oxidase complex and that this complex may share a subunit (SoxC) with the SoxABCD complex.

The Archaeal SoxABCD Complex Is a Proton Pump in Sulfolobus acidocaldarius

“…47 and 48). While the supercomplex "SoxM" (45) could not be isolated in catalytically sufficiently active form, the SoxABCD complex described here has been identified in previous works as a highly active quinol oxidase, using the genustypical caldariella quinol (49) as its natural substrate. Here we have demonstrated for the first time that this integrated Sox-ABCD complex represents a respiratory proton pump, while evidence can be derived from structural properties that its cytochrome aa 3 moiety itself has no proton pumping capacity (see below).…”

“…Two terminal oxidases have been identified in its plasma membrane (8,45,46) and genetically characterized (13,29). Both are sharing an unusual complexity compared with other procaryotic cytochrome c or quinol oxidases (for a review see Refs.…”

Two different respiratory Rieske proteins are expressed in the extreme thermoacidophilic crenarchaeon Sulfolobus acidocaldarius: cloning and sequencing of their genes

“…Protein chemical [3] and genetic [2] evitook place shortly after the bacteria/archaea separation. A dence suggests that the Rieske-II protein is a component of long, independent evolution of both proteins would explain …”

Structure and Function of CytochromebcComplexes

“…The three archaeal sequences have 13 residues in both helices as in the mitochondrial cytochrome. Two of these are from Sulfolobus acidocaldarius, and seem to function as parts of quinol oxidase complexes which, unlike the bacterial quinol oxidases, combine the functionality and the proteins of a cyt bc 1 complex and a cytochrome oxidase (58). A second characteristic is the type of residue that aligns with the highly conserved H202 in yeast mitochondrial bc 1 , which has been shown to be a ligand for quinone at the Q i site.…”

“…Two archaebacterial oxidases, which contain homologs of cytochrome b, have been isolated from Sulfolobus acidocaldarius by Lubben and coworkers (56)(57)(58). One of them also contains a homolog of the Rieske ISP.…”