Dissimilatory Adenosine‐5′‐Phosphosulfate Reductase

Abstract

The iron‐sulfur flavoenzyme adenosine‐5′‐phosphosulfate reductase (APSR) catalyzes the reductive cleavage of APS (adenosine‐5′‐phosphosulfate) to sulfite plus AMP and the reverse reaction, both important reactions within the biogeochemical sulfur cycle. The structure of the dissimilatory enzyme from the hyperthermophilic sulfate reducer Archaeoglobus fulgidus at 1.6 Å resolution reveals APSR as heterotetrameric α 2 ß 2 complex; however, the αß heterodimer is the functionally active unit. The FAD(flavin adenine dinucleotide) binding α‐subunit of APSR is structurally similar to the corresponding subunit of fumarate reductases, suggesting a common ancestor that resembles archaeal APSR. A clear separation is observed between the electron transfer process that extends over 25 Å from the protein surface via two [4Fe‐4S] clusters to the si ‐side of FAD and the chemical process of APS reduction at the re ‐side of FAD. The structures of APSR complex with the substrates APS, sulfite, and AMP trapped the enzyme in four different states and allowed, together with information from spectroscopic studies, to develop a detailed picture of the catalytic cycle. The nucleophilic attack of the N5 atom of FADH − onto the sulfur of APS, both negatively charged, proceeds in a compressed enzyme‐substrate complex relaxed in the formed FAD‐APS and FAD‐sulfite adducts.

Conserving energy with sulfate around 100 °C – structure and mechanism of key metal enzymes in hyperthermophilic Archaeoglobus fulgidus

“…68 These biochemical data were confirmed by the crystal structures of APSR from A. fulgidus (1.6 Å) 77 and D. gigas (3.1 Å), 78 and opened the door to compare the overall architecture and cofactors of these enzymes, and to develop a structure based catalytic mechanism. 79,80 Fig. 2 Structural model of the ATPS homodimer from A. fulgidus based on the three-dimensional structure of ATPS from T. thermophilus (PDB code 1V47).…”

“…This structure shows how the phosphate of AMP and the sulfite of the FAD-sulfite adduct (both negatively charged) are kept in van der Waals contact. 79,80 Fig. 8 Reaction of APSR from A. fulgidus.…”

“…(C) The postulated short-lived FAD-APS intermediate was modeled. 79,80 This journal is c The Royal Society of Chemistry 2013 Metallomics, 2013, 5, 302--317 309 an in-line mechanism for the sulfuryl transfer. It is unknown whether the sulfonation reaction of APSR proceeds by an associative or a dissociative mechanism.…”

DiSCo: a sequence-based type-specific predictor of Dsr-dependent dissimilatory sulphur metabolism in microbial data

“…Interestingly, our AprA-like and AprB-like models led to the identification of this alternate complex in 63 micro-organisms belonging mostly to the class Clostridia, but also to Negativicutes, Deltaproteobacteria, Nitrospira and Archaeoglobi (Table S9), including nine micro-organisms known to contain the Dsr-pathway. A comparison of the AprAB-like proteins with the fold regions of bona-fide AprAB proteins [ 92 ] showed that while the AprB-like protein shares the ferredoxin domain with bona-fide AprB, it lacks its terminal tail responsible for interactions with the AprA subunit [ 92 ]. The alignment of selected AprA-like protein with bona-fide AprA proteins displayed gaps in the capping domain and in the C-terminal, helical domain (for definition of the domains see [ 92 ]).…”

“…A comparison of the AprAB-like proteins with the fold regions of bona-fide AprAB proteins [ 92 ] showed that while the AprB-like protein shares the ferredoxin domain with bona-fide AprB, it lacks its terminal tail responsible for interactions with the AprA subunit [ 92 ]. The alignment of selected AprA-like protein with bona-fide AprA proteins displayed gaps in the capping domain and in the C-terminal, helical domain (for definition of the domains see [ 92 ]). A closer inspection of the genomic neighbourhood of the aprAB -like genes showed an enrichment in sulphur assimilation and processing genes such as assimilatory sulphate adenylyltransferases ( sat , cysD , cysC ), anaerobic sulphite reductase (either asrABC or only the asrC subunit) and genes of several proteins involved in intracellular sulphur trafficking such as TusA, ThiI/F, IscU and IscI.…”