The Archaeal SoxABCD Complex Is a Proton Pump in Sulfolobus acidocaldarius

Abstract

The thermoacidophilic archaeon Sulfolobus acidocaldarius expresses a very unusual quinol oxidase, which contains four heme a redox centers and one copper atom. The enzyme was solubilized with dodecyl maltoside and purified to homogeneity by a combination of hydrophobic interaction and anion exchange chromatography. The oxidase complex consists of four polypeptide subunits with apparent molecular masses of 64, 39, 27, and 14 kDa that are encoded by the soxABCD operon (Lü bben, M., Kolmerer, B., and Saraste, M. (1992) EMBO J. 11, 805-812). The optical spectra and redox potentials of the SoxABCD complex have been characterized, and the absorption coefficients of the contributing cytochromes a 587 and aa 3 were determined. The EPR spectra indicate the presence of three low spin and one high spin heme species, the latter associated with the binuclear heme Cu B site. Standard midpoint potentials of the cytochrome a 587 heme centers were determined as ؉210 and ؉270 mV, respectively. The maximum turnover of the complex (1300 s ؊1 at 65°C) was found to be about three times greater than that of the previously studied isolated cytochrome aa 3 subunit alone (Gleissner, ؉ /e ؊ ratio >1 was determined, identifying the SoxABCD complex as a proton-pumping quinol oxidase. According to structural analysis, the cytochrome aa 3 moiety of the complex does not contain the signature of a H ؉ pumping channel as identified in Rhodobacter sphaeroides or Paracoccus denitrificans. Therefore, for H ؉ translocation, a mechanism different from that in typical heme-copper oxidases of the aa 3 or bo 3 type is discussed.M

The ATPases CopA and CopB both contribute to copper resistance of the thermoacidophilic archaeon Sulfolobus solfataricus

“…The bb 3 -and aa 3 -type cytochrome oxidase activities of membranes, measured by the fully cyanide-sensitive electron transfer from the pseudo-substrate TMPD (Lübben et al, 1994;Gleissner et al, 1997) further supported the abovementioned spectroscopic observations. As shown in Table 2, Fig.…”

Identification of Components of Electron Transport Chains in the Extremely Thermoacidophilic Crenarchaeon Metallosphaera sedula through Iron and Sulfur Compound Oxidation Transcriptomes

“…The SoxABCL terminal oxidase cluster is based on both quinol oxidase (SoxCL) and cytochrome oxidase (SoxAB) components (2,16,35). As expected (2,27), soxABCL, Msed0288 to Msed0291, was significantly upregulated on both YS and YKT (15-fold for Msed0285) media compared to YFS medium (Fig.…”

“…The purpose for near duplication is not clear, although in the case of cbsA and foxAAЈ, the difference in transcriptional profile suggests some differences in regulation and, thus, the potential for functional distinction. It has been noted that while cytochromes b (a 586 ), SoxC and SoxG, from S. acidocaldarius have significant sequence similarity, the redox potential of SoxG is considerably lower than that of SoxC, impacting electron donor/acceptor options (16,29). However, in Rubrivivax gelatinosus, similar Rieske subunits of the bc 1 complex are known to substitute for each other to retain complex functionality (38).…”

“…Reduced quinones (typically caldariella or Sulfolobus-type quinones) then deliver electrons to one of several terminal oxidase complexes, composed of cytochrome oxidase and/or bc 1 complex-like subunits. These subunits are related to aa 3 terminal oxidase complexes in A. ambivalens (DoxBCE) (14,37,42) and Sulfolobus acidocaldarius (SoxABCD-SoxL) (16,34,35), the bb 3 terminal oxidase complex in S. acidocaldarius (SoxEFGHIM) (11,29,33), the putative FoxAB terminal oxidase in S. metallicus (the recent discovery of which coincided with the first report of ferrous iron oxidation in S. tokodaii) (5), and bc 1 -complex in S. acidocaldarius (SoxLN) (22). Both FoxAB and SoxNL are associated with cytochrome b 558/566 -like proteins (FoxCD and CbsAB), which exhibit characteristics found in other terminal oxidase subunits (i.e., glycosylated like SoxBC and conformational flexibility like Rieske proteins) and are probably involved in ETC in a similar manner (5,21,22,37,47).…”

Regulation of the aerobic respiratory chain in the facultatively aerobic and hyperthermophilic archaeon Pyrobaculum oguniense

“…In addition Sulfolobus acidocaldarius and S. tokodaii have alternative electron carriers for cytochrome c such as sulfocyanin or cytochrome a (Gleißner et al, 1997;Iwasaki et al, 1995b;Schäfer, 1996;Lübben et al, 1992). Acidianus ambivalens lacks complex III or its alternatives (Purschke et al, 1997).…”