• Prosthetic group features
• Chloroperoxidase (CPO) reaction
• Haem CPO in enzyme databases
• Haem CPO in SWISS­PROT/TREMBL
• Haem CPO in alignment databases
• Haem CPO in 3­D databases
• References

Haem type	Haem iron coordination	Axial iron ligand(s)	Formal iron oxidation/spin states
Haem b	Pentacoordinate	SCys	FeII (S=2); FeIII (S=5/2)
	Hexacoordinate	SCys; OX (X = Cl, Br, I), CO, NO or other ligand	FeII (S=0); FeIII (S=1/2)
	Hexacoordinate	SCys; O (O·)	FeIV (S=1)

Chloroperoxidase (CPO; EC 1.11.1.10) catalyses the halogenation of a number of aliphatic substrates in the reaction (1):

AH + X¯ + H+ + H2O2 AX + 2H2O

(1)

Although the primary biological function of CPO seems to be chlorination, CfCPO also exhibits peroxidase (2), catalase (3) and monooxygenase (4) activities [1]:

2AH2 + H2O2 HA-AH + 2H2O

(2)

The cycle is initiated by hydrogen peroxide or other oxygen atom donor binding to the high­spin, pentacoordinate ferric resting state to give compound I, a porphyrin ­cation radical containing Fe^IV. Then three pathways are available. In the peroxidase mode (2), compound I undergoes one­electron reduction to form compound II, which contains an oxyferryl centre coordinated to a normal (dianionic) porphyrin ligand, with concomitant oxidation of an organic substrate to give a substrate radical (·AH). Compound II is reduced back to the ferric resting state with concomitant one­electron substrate oxidation. In the catalase mode (3), oxidation of an electron donor (H₂O₂) yields O₂ and returns compound I to the native resting state. In the halogenation mode (1), it is proposed that compound I reacts with the halide to form a hypothetical ferric hypohalite adduct termed compound X, which then transfers a halogen atom to the substrate and regenerates the resting state [6, 7]. The resting state and compound I are neutral, while the overall charge on compounds II and X is -1 (cf. catalase and peroxidases) [5].

CfCPO consists of two mainly ­helical domains; the haem is sandwiched between the two domains [8] (see Figure 1CPO a). The fifth (proximal) haem iron ligand is provided by Cys­29, which is located at the N­terminus of the proximal helix. The proximal helix A is roughly perpendicular to the haem plane. The distal helix F contains Glu­183 which is positioned adjacent to the peroxide­binding site (Figure 1CPO b). The catalytic role of Glu­183 is probably similar to that of the distal His in peroxidases, which helps to protonate the oxygen anion. Mn²⁺ ion is octahedrally coordinated by haem propionate, three amino acids and two water molecules (Figure 1CPO c); the role of the Mn²⁺­binding site in CfCPO remains unknown. CfCPO is extensively glycosylated with both N­ and O­linked glycosyl chains [8].

The structure and function of CfCPO is reviewed in Refs. [1, 5, 8-10].

Haem CPO in enzyme databases

ENZYME	LIGAND	BRENDA	Official name	Alternative name
1.11.1.10	1.11.1.10	1.11.1.10	Chloride peroxidase	Chloroperoxidase

Haem CPO in SWISS­PROT/TREMBL

PRXC_CALFU

Chloroperoxidase precursor (EC 1.11.1.10) (chloride peroxidase); Caldariomyces fumago (Leptoxyphium fumago)

Haem CPO in alignment databases

Protein Superfamily	Pfam	LPFC 3­D alignment
03737; chloride peroxidase	-	-

PDB	scop	BSM	RELI Base	Header	¹
1cpo	1cpo	1cpo	1cpo	Chloroperoxidase (complex with Mn2+) (modified with N­acetyl­D­glucosamine, ­D­mannose, xylose and ß­L­arabinose; contains cyclised pyroglutamic acid at N­terminus); Caldariomyces fumago	MS6JT6
2cpo	2cpo	2cpo	2cpo	Chloroperoxidase (complex with Mn2+) (modified with N­acetyl­D­glucosamine and ­D­mannose; contains cyclised pyroglutamic acid at N­terminus); Caldariomyces fumago	MS6JT6

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

References

1. Griffin, B.W. (1991) Chloroperoxidase: a review. In Everse, J., Everse, K.E. and Grisham, M.B., Eds. Peroxidases in Chemistry and Biology. CRC Press, Boca Raton, vol. II, pp. 85-137.
2. Bantleon, R., Altenbuchner, J. and van Pee, K.H. (1994) Chloroperoxidase from Streptomyces lividans: isolation and characterization of the enzyme and the corresponding gene. J. Bacteriol. 176, 2339-2347.
3. Vollenbroek, E.G., Simons, L.H., van Schijndel, J.W., Barnett, P., Balzar, M., Dekker, H., van der Linden, C. and Wever, R. (1995) Vanadium chloroperoxidases occur widely in nature. Biochem. Soc. Trans. 23, 267-271.
4. Chen, Y.P., Lincoln, D.E., Woodin, S.A. and Lovell, C.R. (1991) Purification and properties of a unique flavin­containing chloroperoxidase from the capitellid polychaete Notomastus lobatus. J. Biol. Chem. 266, 23909-23915.
5. Andersson, L.A. and Dawson, L.A. (1991) EXAFS spectroscopy of heme­containing oxygenases and peroxidases. Structure and Bonding 64, 1-40.
6. Dunford, H.B., Lambeir, A.M., Kashem, M.A. and Pickard, M. (1987) On the mechanism of chlorination by chloroperoxidase. Arch. Biochem. Biophys. 252, 292-302.
7. Libby, R.D., Beachy, T.M. and Phipps, A.K. (1996) Quantitating direct chlorine transfer from enzyme to substrate in chloroperoxidase­catalyzed reactions. J. Biol. Chem. 271, 21820-21827.
8. Sundaramoorthy, M., Terner, J. and Poulos, T.L. (1995) The crystal structure of chloroperoxidase: a heme peroxidase-cytochrome P450 functional hybrid. Structure 3, 1367-1378.
9. Dawson, J.H. and Sono, M. (1987) Cytochrome P­450 and chloroperoxidase: thiolate­ligated heme enzymes. Spectroscopic determination of their active site structures and mechanistic implications of thiolate ligation. Chem. Rev. 87, 1255-1276.
10. Dawson, J.H. (1988) Probing structure-function relations in heme­containing oxygenases and peroxidases. Science 240, 433-439.

Bibliography on structural studies of haem chloroperoxidase

Reviews on haem chloroperoxidase