Abstract
The terminal segment of the aerobic respiratory chain of the thermoacidophilic archaeon Sulfolobus sp. strain 7 is an unusual caldariellaquinol oxidase supercomplex, which contains at least one b-type and three spectroscopically distinguishable a-type cytochromes, one copper, and a Rieske-type FeS center. In this paper, we report the purification and characterization of two different forms of the archaeal a-type cytochromes, namely, a three-subunit cytochrome a583-aa3 subcomplex and a single-subunit cytochrome aa3 derived from the cytochrome subcomplex, in order to facilitate further studies on the terminal oxidase segment of Sulfolobus. The optical and EPR spectroscopic analyses suggest the presence of two different low-spin heme centers and one high-spin heme center in the purified cytochrome a583-aa3 subcomplex, and one low-spin and one high-spin hemes in cytochrome aa3, respectively. The Rieske-type FeS center detected in the purified cytochrome supercomplex was absent in two forms of the a-type cytochrome oxidase, indicating its association with cytochrome b562. The crystal field parameters of the lowspin heme a583 center indicate that its axial ligands may be similar to those of cytochromes c, rather than conventional bis-histidine ligation. In spite of the absence of any c-type cytochrome, a ferrocytochrome c oxidase activity was detected in the archaeal purified cytochrome a583-aa3 subcomplex with no quinol oxidase activity, but not in the purified cytochrome oxidase supercomplex, which has been tentatively interpreted as a representative of electron transfer from the Rieske FeS center to cytochrome a583 in vivo. Thus, our results indicate the following scheme for the intramolecular electron transfer of the terminal oxidase supercomplex from Sulfolobus sp. strain 7: [caldariellaquinol-->] b562-->Rieske FeS center-->a583 aa3-->molecular oxygen.
Highlights
The terminal segment of the aerobic respiratory chain of the thermoacidophilic archaeon Sulfolobus sp. strain 7 is an unusual caldariellaquinol oxidase supercomplex, which contains at least one b-type and three spectroscopically distinguishable a-type cytochromes, one copper, and a Rieske-type FeS center
We report the purification and characterization of two different forms of the archaeal a-type cytochromes, namely, a three-subunit cytochrome a583-aa3 subcomplex and a single-subunit cytochrome aa3 derived from the cytochrome subcomplex, in order to facilitate further studies on the terminal oxidase segment of Sulfolobus
In spite of the absence of any c-type cytochrome, a ferrocytochrome c oxidase activity was detected in the archaeal purified cytochrome a583-aa3 subcomplex with no quinol oxidase activity, but not in the purified cytochrome oxidase supercomplex, which has been tentatively interpreted as a representative of electron transfer from the Rieske FeS center to cytochrome a583 in vivo
Summary
The terminal segment of the aerobic respiratory chain of the thermoacidophilic archaeon Sulfolobus sp. strain 7 is an unusual caldariellaquinol oxidase supercomplex, which contains at least one b-type and three spectroscopically distinguishable a-type cytochromes, one copper, and a Rieske-type FeS center. Strain 7 is an unusual caldariellaquinol oxidase supercomplex, which contains at least one b-type and three spectroscopically distinguishable a-type cytochromes, one copper, and a Rieske-type FeS center. The first evidence for the presence of the terminal oxidase supercomplex in archaea came from the genetic and subsequent biochemical studies on the SoxABCD oxidase from the thermoacidophilic archaeon Sulfolobus acidocaldarius strain DSM 639 [10, 26], which appears to consist of a apo-cytochrome b homologue of cytochrome bc complex (SoxC) in addition to subunits I and II of the heme-copper oxidase superfamily and several additional small polypeptides. The SoxM oxidase complex contains a Rieske-type FeS cluster in addition to both protoheme and the heme AS center in a ratio of ϳ1:3 [27]. While both terminal oxidase complexes of S. acidocaldarius apparently contain the apocytochrome b homologue (e.g. SoxC), it remains to be clarified why a Rieske FeS center [28] has been found only in the SoxM oxidase [27] but not in the SoxABCD oxidase [26]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
