STRUCTURAL CHARACTERIZATION OF PARACOCCUS-DENITRIFICANS CYTOCHROME-C PEROXIDASE AND ASSIGNMENT OF THE LOW AND HIGH-POTENTIAL HEME SITES

The amino acid sequence of the diheme cytochrome c peroxidase from Par acoccus denitrificans has been determined as the result of sequence an alysis of peptides generated by chemical and enzymatic cleavages of th e apoprotein. The sequence shows 60% similarity to the cytochrome c pe roxidase from Pseudomonas aeruginosa, 39% similarity to an open readin g frame encoding a putative triheme c-type cytochrome in Escherichia c oli, and remote similarity to the MauG proteins from two methylotrophi c bacteria. It is proposed, on the basis of the pattern of conserved r esidues in the sequences, that a change in iron coordination in the N- terminal heme domain may accompany reduction to the active mixed valen ce state, a change which may be accompanied by conformational adjustme nts in the highly conserved interface between the N- and C-terminal do mains. These conformational adjustments may also lead to the appearanc e of a second Ca2+ binding site in the mixed valence enzyme. The expos ed edge of the heme in the C-terminal domain is surrounded by several different patterns of charged residues in the Paracoccus and Pseudomon as enzymes, and this is consistent with the interaction of the former with the highly positively charged front face of the donor cytochrome c-550.