• Prosthetic group features
• Cytochrome cd₁ in enzyme databases
• Cytochrome cd₁ in motif databases
• Cytochrome cd₁ in alignment databases
• Cytochrome cd₁ in 3­D databases
• References

Haem type	Haem iron coordination	Axial iron ligands	Formal iron oxidation/spin states
Haem c	T. pantotropha (oxidised)		FeIII (S=1/2)
	Hexacoordinate	NHis; NHis
	Ps. aeruginosa (oxidised); T. pantotropha (reduced)		FeII (S=0); FeIII (S=1/2)
	Hexacoordinate	NHis; SMet
Haem d1	Pentacoordinate	NHis	FeII (S=2); FeIII (S=5/2)
	Hexacoordinate	NHis; NO, NO2¯, O2 or other ligand	FeII (S=0); FeIII (S=1/2)
	T. pantotropha (oxidised)		FeIII (S=1/2)
	Hexacoordinate	NHis; OTyr
	Ps. aeruginosa (oxidised)
	Hexacoordinate	NHis; OH¯

Cytochrome cd₁ nitrite reductase (cytochrome oxidase; EC 1.9.3.2) is a bifunctional enzyme that catalyses both the one­electron reduction of nitrite to nitric oxide (1) and the four­electron reduction of oxygen to water (2) [1].

NO2¯ + 2H+ + e¯ NO + 2H2O

(1)

The 3­D structures of cyt cd₁ from Thiosphaera pantotropha [5] and Pseudomonas aeruginosa [6] have been determined. The monomers consist of two structural domains: an N­terminal ­helical c­domain and a C­terminal ß­propeller d₁­domain. In spite of similar architecture, the structure of haem­binding sites differs significantly in the two enzymes. In the oxidised T. pantotropha cyt cd₁, His­17 and His­69 provide the axial iron ligands for haem c; His­200 is a fifth axial iron ligand for haem d₁. An unusual feature of cyt cd₁ is that the main chain of the c­domain makes an excursion into the d₁­domain, providing Tyr­25 as the sixth axial iron ligand for haem d₁ [5]. Upon reduction, Tyr­25 is released to allow substrate binding to the haem d₁; concomitantly, a `refolding' of the c­domain takes place, resulting in a switch of one haem c iron ligand from His­17 to Met­106 [7]. In the oxidised Ps. aeruginosa protein, His­51 and Met­88 provide the axial iron ligands for haem c and His­182 provides the fifth axial iron ligand for haem d₁. The hydroxide ion, hydrogen bonded to Tyr­10, is a sixth axial iron ligand for haem d₁ [6].

Cytochrome cd₁ in enzyme databases

ENZYME	LIGAND	BRENDA	Official name	Alternative names
1.9.3.2	1.9.3.2	1.9.3.2	Pseudomonas cytochrome oxidase	Cytochrome c­551:O2, NO2¯ oxidoreductase; cytochrome cd; cytochrome cd1; nitrite reductase

Cytochrome cd₁ in motif databases

PRINTS ID	PRINTS AC	PROSITE/BLOCKS ID	PROSITE AC	BLOCKS AC
-	-	CYTOCHROME_C	PS00190	BL00190

Cytochrome cd₁ in alignment databases

Protein Superfamily	Pfam	LPFC 3­D alignment
00164; Pseudomonas cytochrome oxidase	-	-

PDB	MSD	scop	BSM	RELI Base	Header	¹
1aof	1aof	1aof	1aof	1aof	Cytochrome cd1 nitrite reductase (reduced) (complex with SO2); Thiosphaera pantotropha	MS6HW6
1aom	1aom	-	1aom	1aom	Cytochrome cd1 nitrite reductase (complex with NO2 and NO); Thiosphaera pantotropha	-
1aoq	1aoq	-	1aoq	1aoq	Cytochrome cd1 nitrite reductase (complex with NO2 and NO); Thiosphaera pantotropha	-
1nir	1nir	-	1nir	1nir	Cytochrome cd1 nitrite reductase (oxidised) (complex with Cl¯, OH¯ and PO43+); Pseudomonas aeruginosa	-
-	-	-	-	-	Cytochrome cd1 nitrite reductase (oxidised) (complex with glycerol and SO2); Thiosphaera pantotropha	-

¹ Macromolecular Structures abstract. Full text is available to BioMedNet Members

References

1. Silvestrini, M.­C., Falcinelli, S., Ciabatti, I., Cutruzzolà, F. and Brunori, M. (1994) Pseudomonas aeruginosa nitrite reductase (or cytochrome oxidase): An overview. Biochimie 76, 641-654.
2. Henry, Y. and Bessieres, P. (1984) Denitrification and nitrite reduction: Pseudomonas aeruginosa nitrite­reductase. Biochimie 66, 259-289.
3. Brittain, T., Blackmore, R., Greenwood, C. and Thomson, A.J. (1992) Bacterial nitrite­reducing enzymes. Eur. J. Biochem. 209, 793-802.
4. Silvestrini, M.­C., Cutruzzolà, F., Schinina, M.E., Maras, B. and Rolli, G. (1996) Isolation and characterization of the d₁ domain of Pseudomonas aeruginosa nitrite reductase. J. Inorg. Biochem. 62, 77-87.
5. Fülöp, V., Moir, J.W.B., Ferguson, S.J. and Hajdu, J. (1995) The anatomy of a bifunctional enzyme: structural basis for reduction of oxygen to water and synthesis of nitric oxide by cytochrome cd₁. Cell 81, 369-377.
6. Nurizzo, D., Silvestrini, M.­C., Mathieu, M., Cutruzzolà, F. Bourgeois, D., Fülöp, V., Hajdu, J., Brunori, M., Tegoni, M. and Cambillau, C. (1997) N­terminal arm exchange is observed in the 2.15 Å crystal structure of oxidized nitrite reductase from Pseudomonas aeruginosa. Structure 5, 1157-1171.
7. Williams, P.A., Fülöp, V., Garman, E.F., Saunders, N.F.W., Ferguson, S.J. and Hajdu, J. (1997) Haem­ligand switching during catalysis in crystals of a nitrogen­cycle enzyme. Nature 389, 406-412.

Bibliography on structural studies of cytochrome cd1