Publication Date:
2015-02-03
Description:
The six-electron reduction of sulfite to sulfide is the pivot point of the biogeochemical cycle of the element sulfur. The octahaem cytochrome c MccA (also known as SirA) catalyses this reaction for dissimilatory sulfite utilization by various bacteria. It is distinct from known sulfite reductases because it has a substantially higher catalytic activity and a relatively low reactivity towards nitrite. The mechanistic reasons for the increased efficiency of MccA remain to be elucidated. Here we show that anoxically purified MccA exhibited a 2- to 5.5-fold higher specific sulfite reductase activity than the enzyme isolated under oxic conditions. We determined the three-dimensional structure of MccA to 2.2 A resolution by single-wavelength anomalous dispersion. We find a homotrimer with an unprecedented fold and haem arrangement, as well as a haem bound to a CX15CH motif. The heterobimetallic active-site haem 2 has a Cu(I) ion juxtaposed to a haem c at a Fe-Cu distance of 4.4 A. While the combination of metals is reminiscent of respiratory haem-copper oxidases, the oxidation-labile Cu(I) centre of MccA did not seem to undergo a redox transition during catalysis. Intact MccA tightly bound SO2 at haem 2, a dehydration product of the substrate sulfite that was partially turned over due to photoreduction by X-ray irradiation, yielding the reaction intermediate SO. Our data show the biometal copper in a new context and function and provide a chemical rationale for the comparatively high catalytic activity of MccA.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Hermann, Bianca -- Kern, Melanie -- La Pietra, Luigi -- Simon, Jorg -- Einsle, Oliver -- England -- Nature. 2015 Apr 30;520(7549):706-9. doi: 10.1038/nature14109. Epub 2015 Feb 2.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lehrstuhl Biochemie, Institut fur Biochemie, Albert-Ludwigs-Universitat Freiburg, Albertstrasse 21, 79104 Freiburg, Germany. ; Microbial Energy Conversion &Biotechnology, Department of Biology, Technische Universitat Darmstadt, Schnittspahnstrasse 10, 64287 Darmstadt, Germany. ; 1] Lehrstuhl Biochemie, Institut fur Biochemie, Albert-Ludwigs-Universitat Freiburg, Albertstrasse 21, 79104 Freiburg, Germany [2] BIOSS Centre for Biological Signalling Studies, Schanzlestrasse 1, 79104 Freiburg, Germany.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25642962" target="_blank"〉PubMed〈/a〉
Keywords:
Bacterial Proteins/*chemistry/isolation & purification/metabolism
;
Biocatalysis
;
Catalytic Domain
;
Copper/*metabolism
;
Crystallography, X-Ray
;
Cysteine/analogs & derivatives/metabolism
;
Heme/*analogs & derivatives/metabolism
;
Models, Molecular
;
Oxidation-Reduction
;
Oxidoreductases Acting on Sulfur Group Donors/*chemistry/isolation &
;
purification/metabolism
;
Sulfites/metabolism
;
Sulfur Dioxide/metabolism
;
Wolinella/*enzymology
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
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