Respiratory sulfite reductase that catalyzes the reduction of sulfite to sulfide in a single step, consuming six electrons in the process. Required for sulfite respiration under anaerobic growth conditions. Has only marginal activity with nitrite. [protein]-disulfide + 2 A + 3 H2O + hydrogen sulfide = [protein]-dithiol + 2 AH2 + H+ + sulfite.

MLSGWSVLKGGNMKYWDKALLSLFMCVSTLSIAATHAVAMEGMQMTKEAREIIAHPKGTK ESRGVISLQDYIVEEQAMYDWLFKNHPIFTKYGGKTVGKLVVKDRGEEWIEEGRGNDFSK ASKRSGGEGFSSMMYRVARNSTLQYPNKFIGPEKCGECHPAQYETWSRSRHATTIRFPGE HPEVNNKLNDPVFDKDTASILPQGITPDVVYCTVGHIRTKFGFFDAWLLRGTYHVEGGLL KNGTGQIVAGGNQWQRTWALNLSPEVAKKIKKWVPDFPVTLEEYGDNGGYVRGLASYAAK YKKSMSFQASTSYCEVCHPWKFDFKNESEFYAALGNAKELQKHTISKGVSCEECHGAGGH LEGGSGLLISNCERCHQRFSYSPDLMRNNPLNAGKPDLALSSKFKSMGPGCGSEGSQTYF TAHYEKGMRCATCHDPHDVTGNVTGEKGIKGVSYNSEQGYLSSLYSKPKLKKECTDCHKE QAYIQSKADTHSKNSCASCHMPFMMSCENFYAIQFQDQAGFDTQRRAHIWKIDVDPARKS LVAGSTSKDPRDGKDWHFERNEEGRNFVDLMWACARTTWADKDQAEAKGCHSPVVSELKE TLHFKDQKQVYNEVMGWQTPVKDKFTQVKVGIQGLYSLLEVKKLAPSDKTRVYELIEKAQ DTVDLIEKDGSWGMHGFKYTKQRLDAAVEYINEAQRIMKKSL713

	PMID	Title & Author	Abstract	Year
0	25642962	The octahaem MccA is a haem c-copper sulfite reductase.Bianca Hermann , Melanie Kern , Luigi La Pietra , Jörg Simon , Oliver Einsle	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 Å 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 Å. 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.	2015
1	30342041	Significance of MccR, MccC, MccD, MccL and 8-methylmenaquinone in sulfite respiration of Wolinella succinogenes.Jakob Eller , Sascha Hein , Jörg Simon	Reduction of sulfite to sulfide is an essential step in the biogeochemical sulfur cycle. The Epsilonproteobacterium Wolinella succinogenes uses the copper-containing octahaem cytochrome c sulfite reductase MccA to respire sulfite. MccA is encoded by the first gene of the mcc gene cluster, whose transcription is apparently induced by the two-component regulatory system MccRS. It has been proposed that the iron‑sulfur protein MccC, the putative quinol dehydrogenase MccD, the copper chaperone MccL as well as menaquinone-6 (MK6) and/or 8-methylmenaquinone-6 (8-MMK6) are involved in the electron transport chain of W. succinogenes sulfite respiration. Here, non-polar W. succinogenes mutants were constructed that lacked MccC, MccD, MccL or the 8-MMK6-producing MK6 methyltransferase MqnK. Each mutant possessed a frameshift-corrected mccR gene, thus inducing mcc expression in the presence of a mixture of fumarate and sulfite as terminal electron acceptors. Under these conditions, growth by sulfite respiration of cells lacking MccA, MccC or MccD was found to be abolished. However, cells lacking MccL or 8-MMK6 still coupled formate oxidation to sulfite reduction and grew by sulfite respiration to some extent. The results indicate that MccR, MccC, MccD, MccL and 8-MMK6 are essential or significant components of W. succinogenes sulfite respiration.	2018
2	22040142	The Wolinella succinogenes mcc gene cluster encodes an unconventional respiratory sulphite reduction system.Melanie Kern, Martin G Klotz, Jörg Simon	Assimilatory and dissimilatory sulphite reductions are key reactions in the biogeochemical sulphur cycle and several distinct sirohaem-containing sulphite reductases have been characterized. Here, we describe that the Epsilonproteobacterium Wolinella succinogenes is able to grow by sulphite respiration (yielding sulphide) with formate as electron donor. Sulphite is reduced by MccA, a prototypical member of an emerging new class of periplasmic cytochrome c sulphite reductases that, phylogenetically, belongs to a multihaem cytochrome c superfamily whose members play crucial roles in the global sulphur and nitrogen cycles. Within this family, MccA represents an unconventional octahaem cytochrome c containing a special haem c group that is bound via two cysteine residues arranged in a unique CX(15)CH haem c binding motif. The phenotypes of numerous W.succinogenes mutants producing MccA variants underlined the structural importance of this motif. Several open reading frames of the mcc gene cluster were individually inactivated and characterization of the corresponding mutants indicated that the predicted iron-sulphur protein MccC, the putative quinol dehydrogenase MccD (a member of the NrfD/PsrC family) as well as a peptidyl-prolyl cis-trans isomerase, MccB, are essential for sulphite respiration. MccA synthesis in W. succinogenes was found to be induced by sulphite (but not by thiosulphate or sulphide) and repressed in the presence of fumarate or nitrate. Based on the results, a sophisticated model of respiratory sulphite reduction by the Mcc system is presented.	2011

Kern M , Klotz M G , Simon J . The Wolinella succinogenes mcc gene cluster encodes an unconventional respiratory sulphite reduction system[J]. Molecular Microbiology, 2011, 82(6):1515-1530.