Abstract
BackgroundThe bioenergetics of Archaea with respect to the evolution of electron transfer systems is very interesting. In contrast to terminal oxidases, a canonical bc1 complex has not yet been isolated from Archaea. In particular, c-type cytochromes have been reported only for a limited number of species.ResultsHere, we isolated a c-type cytochrome-containing enzyme complex from the membranes of the hyperthermophilic archaeon, Aeropyrum pernix, grown aerobically. The redox spectrum of the isolated c-type cytochrome showed a characteristic α-band peak at 553 nm corresponding to heme C. The pyridine hemochrome spectrum also revealed the presence of heme B. In non-denaturing polyacrylamide gel electrophoresis, the cytochrome migrated as a single band with an apparent molecular mass of 80 kDa, and successive SDS-PAGE separated the 80-kDa band into 3 polypeptides with apparent molecular masses of 40, 30, and 25 kDa. The results of mass spectrometry indicated that the 25-kDa band corresponded to the hypothetical cytochrome c subunit encoded by the ORF APE_1719.1. In addition, the c-type cytochrome-containing polypeptide complex exhibited menaquinone: yeast cytochrome c oxidoreductase activities.ConclusionIn conclusion, we showed that A. pernix, a hyperthemophilic archaeon, has a "full" bc complex that includes a c-type cytochrome, and to the best of our knowledge, A. pernix is the first archaea from which such a bc complex has been identified. However, an electron donor candidates for cytochrome c oxidase, such as a blue copper protein, have not yet been identified in the whole genome data of this archaeon. We are currently trying to identify an authentic substrate between a bc complex and terminal oxidase.
Highlights
The bioenergetics of Archaea with respect to the evolution of electron transfer systems is very interesting
A. pernix K1 cells were harvested in the early stationary phase, and membranes were prepared
On the basis of these results, we concluded that cytochrome c553 was part of the cytochrome bc complex and that the 3 bands identified by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) analysis corresponded to cytochrome b, Figure 3 Heme analysis by matrix-assisted laser desorption ionization (MALDI)-TOF mass spectrometry of partially purified cytochrome oa3 oxidase from A. pernix
Summary
The bioenergetics of Archaea with respect to the evolution of electron transfer systems is very interesting. In contrast to terminal oxidases, a canonical bc complex has not yet been isolated from Archaea. Aeropyrum pernix is a hyperthermophilic crenarchaeon isolated from the seas of Japan, and its complete genome sequence has been reported [1,2]. Most of the hyperthermophilic archaea grow anaerobically, but this archaeon is strictly aerobic and grows optimally at 9095°C at neutral pH. Analysis of the respiratory chain of the organism is important for understanding the mechanism of aerobic growth in such environments. There are only a few reports about the bioenergetics of A. pernix. Many bacteria and archaea have 2 to 6 terminal oxidases in the respiratory chain [3]. The heme-copper binding motif, but its substrates have not been identified in the genome sequence
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