| Summary: | Cytochromes P450 (CYP) are monooxygenases participating reactions of the PhaseI in xenobiotic biotransformations. Better and more detailed knowledge of heme - protein interaction is crucial for understanding of function of these enzymes; in particular, of their regulation. We analyzed orientations of both heme vinyl side-chains in all X-ray structures of CYP enzymes available in the PDB data bank. For two mammalian forms, CYP 2A4 and 3A4, a more detailed analysis of the heme contacts with the apoprotein was performed, based on identification of the amino acid side chains in the vicinity. In addition to spatial information, dissociation constants and Coulombic interaction of polar residues in proximity to the heme were calculated using the PropKA web server. Deviations of the heme from planarity in both forms of P450 was investigated using the normal coordinate analysis (NSD server). Distribution of torsion angles of vinyls in position 2 and 4 of the heme shows that the side- chain at position 2 is conformationally more restricted in most P450 forms studied. Comparison of all forms shows that the range of ättainable values of torsional angles is very wide, practically unrestricted, and that the actual conformations of the heme moiety are probably determined more by the interaction with the protein,...
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