An archaebacterial terminal oxidase combines core structures of two mitochondrial respiratory complexes.

Abstract

The operon coding for a respiratory quinol oxidase was cloned from thermoacidophilic archaebacterium Sulfolobus acidocaldarius. It contains three genes, soxA, soxB and soxC. The first two genes code for proteins related to the cytochrome c oxidase subunits II and I, respectively. soxC encodes a protein homologous to cytochrome b, which is a subunit of the mitochondrial and bacterial cytochrome c reductases and the chloroplast cytochrome b6f complex. soxA is preceded by a promoter and the genes are cotranscribed into a 4 kb mRNA. Their protein products form a complex which has been partially purified and has quinol oxidase activity. The reduced minus oxidized absorption spectrum of the complex has two maxima at 586 and 606 nm. The latter is typical of cytochrome c oxidase. The complex contains four haems A. Two haems belong to the ‘cytochrome oxidase’ part of the complex and two are probably bound to be apocytochrome b (SoxC) and responsible for the 586 nm absorption peak. The homology between the sox gene products and their mitochondrial counterparts suggests that energy conservation coupled to the quinol oxidation catalysed either by the Sulfolobus oxidase or two mitochondrial respiratory enzymes may have a similar mechanism.

Mitochondrial cytochrome b: evolution and structure of the protein

“…seen, except for a subunlt of Sulfolobus qulnol oxadase [70], in other dlheme m e m b r a n e cytochromes (e g , cytochrome b-558 of E coh mtrate reductase [71] or the largest subunlt of cytochrome oxadase [70])…”

“…Chlorobtum hmwola (G Hauska, unpubhshed), Hehobactllus chlorus (V Vermaas, unpubhshed), Bacdlus PS3 (b6-hke) [82], Sulfolobus actdocaldarms (SoxC subumt binding heme a m a qumol oxldase) [70] Cytochrome b 6 of the cytochrome b6f complex…”

A Second Terminal Oxidase in Sulfolobus acidocaldarius

“…potassium glutamate. Total RNA was prepared from logarithmically growing cells (absorbance of 0.2-0.5 at 600nm) as described earlier (Liibben et al, 1992). The probe in Northern blots was the 3ZP-labelled 2.2-kb insert of pE2.2 (Fig.…”

“…We have constructed a plasmid, pLP4, which carries a 6.5-kb SulI-XbaI fragment containing almost the entire soxABCD operon. This includes the suxB gene which codes for cytochrome oxidase subunit I (Liibben et al, 1992). Fig.…”

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

“…However, there is no lobus proteins. While it is 12-18 residues for other proteins it protein chemical or genetic evidence [16] for an association is 24 amino acids in the case of the Rieske-II protein and even of the Rieske-I with the other quinol-oxidase (SoxABCD) of 44 residues in the case of the Rieske-I protein. At present Sulfolobus, especially since the SoxABCD oxidase can be there is no obvious reason for this enlarged distance.…”