Abstract
Disulfide reductases reduce other proteins and are critically important for cellular redox signaling and homeostasis. Methanosarcina acetivorans is a methane-producing microbe from the domain Archaea that produces a ferredoxin:disulfide reductase (FDR) for which the crystal structure has been reported, yet its biochemical mechanism and physiological substrates are unknown. FDR and the extensively characterized plant-type ferredoxin:thioredoxin reductase (FTR) belong to a distinct class of disulfide reductases that contain a unique active-site [4Fe-4S] cluster. The results reported here support a mechanism for FDR similar to that reported for FTR with notable exceptions. Unlike FTR, FDR contains a rubredoxin [1Fe-0S] center postulated to mediate electron transfer from ferredoxin to the active-site [4Fe-4S] cluster. UV-visible, EPR, and Mössbauer spectroscopic data indicated that two-electron reduction of the active-site disulfide in FDR involves a one-electron-reduced [4Fe-4S]1+ intermediate previously hypothesized for FTR. Our results support a role for an active-site tyrosine in FDR that occupies the equivalent position of an essential histidine in the active site of FTR. Of note, one of seven Trxs encoded in the genome (Trx5) and methanoredoxin, a glutaredoxin-like enzyme from M. acetivorans, were reduced by FDR, advancing the physiological understanding of FDR's role in the redox metabolism of methanoarchaea. Finally, bioinformatics analyses show that FDR homologs are widespread in diverse microbes from the domain Bacteria.
Highlights
The authors declare that they have no conflicts of interest with the contents of this article
Methanosarcina acetivorans, classified in the domain Archaea, produces a planttype ferredoxin:disulfide reductase (FDR) devoid of flavin that contains an active-site [Fe4S4] cluster revealed by the crystal structure (5)
A major advance toward the mechanistic and physiological understanding of FDR from M. acetivorans was accomplished with comprehensive experimental approaches that included EPR and Mossbauer spectroscopy, and site-specific variants
Summary
The authors declare that they have no conflicts of interest with the contents of this article. Plant ferredoxin:thioredoxin reductase (FTR) is devoid of flavin and contains a novel active-site [Fe4S4] cluster (3, 4). Methanosarcina acetivorans, classified in the domain Archaea, produces a planttype ferredoxin:disulfide reductase (FDR) devoid of flavin that contains an active-site [Fe4S4] cluster revealed by the crystal structure (5). Trxs are small redox proteins that reduce the disulfide bonds of proteins that are key to controlling a diverse array of essential processes in organisms from the domains Bacteria and Eukarya (1). The methanoarchaea play an essential role in the global carbon cycle They are terminal organisms of microbial food chains, converting complex biomass to methane in a diverse set of anaerobic environments, annually producing nearly one billion tons of methane that contributes significantly to the greenhouse effect (11). It is of ecological importance to understand the physiology and biochemistry of redox control and response to oxidative stress in methanoarchaea
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