3MM6

Dissimilatory sulfite reductase cyanide complex

Summary for 3MM6

• Entry DOI: 10.2210/pdb3mm6/pdb
• Descriptor: Sulfite reductase, dissimilatory-type subunit alpha, Sulfite reductase, dissimilatory-type subunit beta, SIROHEME, ... (6 entities in total)
• Functional Keywords: alpha-beta-protein, oxidoreductase
• Biological source: Archaeoglobus fulgidus; More
• Cellular location: Membrane: Q59109 Q59110
• Total number of polymer chains: 4
• Total formula weight: 184981.01

Authors

Parey, K.,Warkentin, E.,Kroneck, P.M.H.,Ermler, U. (deposition date: 2010-04-19, release date: 2010-07-21, Last modification date: 2024-10-30)

Primary citation

Parey, K.,Warkentin, E.,Kroneck, P.M.,Ermler, U.
Reaction cycle of the dissimilatory sulfite reductase from Archaeoglobus fulgidus.
Biochemistry, 49:8912-8921, 2010

PubMed Abstract: A vital process in the biogeochemical sulfur cycle is the dissimilatory sulfate reduction pathway in which sulfate (SO₄⁻²) is converted to hydrogen sulfide (H₂S). Dissimilatory sulfite reductase (dSir), its key enzyme, hosts a unique siroheme-[4Fe-4S] cofactor and catalyzes the six-electron reduction of sulfite (SO₃²⁻) to H₂S. To explore this reaction, we determined the X-ray structures of dSir from the archaeon Archaeoglobus fulgidus in complex with sulfite, sulfide (S²⁻) carbon monoxide (CO), cyanide (CN⁻), nitrite (NO₂⁻), nitrate (NO₃⁻), and phosphate (PO₄³⁻). Activity measurements indicated that dSir of A. fulgidus reduces, besides sulfite and nitrite, thiosulfate (S₂O₃²⁻) and trithionate (S₃O₆²⁻) and produces the latter two compounds besides sulfide. On this basis, a three-step mechanism was proposed, each step consisting of a two-electron transfer, a two-proton uptake, and a dehydration event. In comparison, the related active site structures of the assimilatory sulfite reductase (aSir)- and dSir-SO₃²⁻complexes reveal different conformations of Argα170 and Lysα211 both interacting with the sulfite oxygens (its sulfur atom coordinates the siroheme iron), a sulfite rotation of ~60° relative to each other, and different access of solvent molecules to the sulfite oxygens from the active site cleft. Therefore, solely in dSir a further sulfite molecule can be placed in van der Waals contact with the siroheme-ligated sulfite or sulfur-oxygen intermediates necessary for forming thiosulfate and trithionate. Although reported for dSir from several sulfate-reducing bacteria, the in vivo relevance of their formation is questionable.

PubMed: 20822098
DOI: 10.1021/bi100781f

Experimental method

X-RAY DIFFRACTION (1.9 Å)