CcNiR

From Proteopedia

CYTOCHROME C NITRITE REDUCTASE FROM DESULFOVIBRIO DESULFURICANS ATCC 27774 (PDB entry 1oah) Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image The dissimilatory cytochrome 𝑐 nitrite reductase (ccNiR) from Desulfovibrio desulfuricans ATCC 27774 is able to reduce nitrite to ammonia in a six-electron transfer reaction[1] [2] [3] [4] [5] [6]: NO2− + 8H+ + 6e− → NH4+ + 2H2O This reaction is involved in a respiratory process that represents an important branch of the biological nitrogen cycle. The physiological form of the enzyme is believed to be a double trimer of 2 NrfA and 1 NrfH subunits (2j7a)[7]. The catalytic subunit NrfA is a pentaheme cytochrome c where the short distances between allow a fast and efficient electron transfer; the active site) has been reported as an unusual lysine-coordinated high-spin heme. NrfH is a small membrane-bound cytochrome comprising four c-type heme groups and it serves a double purpose: on one hand, it anchors the catalytic subunits to the membrane. On the other hand, it serves as a quinol oxidase, transferring electrons from the quinone pool to the catalytic subunits [8]. The overall haem arrangement of the NrfHA complex is rather unusal, comprising 28 hemes in a highly compact arrangement.

Cytochrome c nitrite reductase is a multicenter enzyme that uses a five-coordinated heme to perform the reduction of nitrite to ammonium in a six-electron transfer reaction. In the sulfate reducing bacterium Desulfovibrio desulfuricans ATCC 27774, the enzyme is purified as a NrfA4NrfH4 complex that houses 28 hemes.

All but the active centre at the pentahemic subunit NrfA are hexa-coordinated c-type hemes whereas the catalytic heme is bound to a lysine as the fifth coordinate ligand and has the sixth axial position available for substrate binding. NrfA is strongly bound to its physiological electron donor, the smaller hydrophobic polypeptide tetrahemic NrfH, composed of 4 c-types hemes; in vitro, the protein complexes associate each other forming huge aggregates (min. 890 kDa).

1. ↑ Almeida MG, Macieira S, Goncalves LL, Huber R, Cunha CA, Romao MJ, Costa C, Lampreia J, Moura JJ, Moura I. The isolation and characterization of cytochrome c nitrite reductase subunits (NrfA and NrfH) from Desulfovibrio desulfuricans ATCC 27774. Re-evaluation of the spectroscopic data and redox properties. Eur J Biochem. 2003 Oct;270(19):3904-15. PMID:14511372
2. ↑ Cunha CA, Macieira S, Dias JM, Almeida G, Goncalves LL, Costa C, Lampreia J, Huber R, Moura JJ, Moura I, Romao MJ. Cytochrome c nitrite reductase from Desulfovibrio desulfuricans ATCC 27774. The relevance of the two calcium sites in the structure of the catalytic subunit (NrfA). J Biol Chem. 2003 May 9;278(19):17455-65. Epub 2003 Mar 4. PMID:12618432 doi:10.1074/jbc.M211777200
3. ↑ Costa C, Moura JJ, Moura I, Wang Y, Huynh BH. Redox properties of cytochrome c nitrite reductase from Desulfovibrio desulfuricans ATCC 27774. J Biol Chem. 1996 Sep 20;271(38):23191-6. PMID:8798514
4. ↑ Almeida MG, Silveira CM, Guigliarelli B, Bertrand P, Moura JJ, Moura I, Leger C. A needle in a haystack: the active site of the membrane-bound complex cytochrome c nitrite reductase. FEBS Lett. 2007 Jan 23;581(2):284-8. Epub 2006 Dec 19. PMID:17207484 doi:10.1016/j.febslet.2006.12.023
5. ↑ Silveira CM, Besson S, Moura I, Moura JJ, Almeida MG. Measuring the cytochrome C nitrite reductase activity-practical considerations on the enzyme assays. Bioinorg Chem Appl. 2010. pii: 634597. Epub 2010 Jun 22. PMID:20689707 doi:10.1155/2010/634597
6. ↑ Almeida MG, Silveira CM, Guigliarelli B, Bertrand P, Moura JJ, Moura I, Leger C. A needle in a haystack: the active site of the membrane-bound complex cytochrome c nitrite reductase. FEBS Lett. 2007 Jan 23;581(2):284-8. Epub 2006 Dec 19. PMID:17207484 doi:10.1016/j.febslet.2006.12.023
7. ↑ Rodrigues ML, Oliveira TF, Pereira IA, Archer M. X-ray structure of the membrane-bound cytochrome c quinol dehydrogenase NrfH reveals novel haem coordination. EMBO J. 2006 Dec 13;25(24):5951-60. Epub 2006 Nov 30. PMID:17139260
8. ↑ Rodrigues ML, Oliveira TF, Pereira IA, Archer M. X-ray structure of the membrane-bound cytochrome c quinol dehydrogenase NrfH reveals novel haem coordination. EMBO J. 2006 Dec 13;25(24):5951-60. Epub 2006 Nov 30. PMID:17139260