Structural and spectroscopic characterization of P450 BM3 mutants with unprecedented P450 heme iron ligand sets: New heme ligation states influence conformational equilibria in P450 BM3

Hazel M. Girvan, Harriet E. Seward, Helen S. Toogood, Myles R. Cheesman, David Leys, Andrew W. Munro

    Research output: Contribution to journalArticlepeer-review

    Abstract

    Two novel P450 heme iron ligand sets were generated by directed mutagenesis of the flavocytochrome P450 BM3 heme domain. The A264H and A264K variants produce Cys-Fe-His and Cys-Fe-Lys axial ligand sets, which were validated structurally and characterized by spectroscopic analysis. EPR and magnetic circular dichroism (MCD) provided fingerprints defining these P450 ligand sets. Near IR MCD spectra identified ferric low spin charge-transfer bands diagnostic of the novel ligands. For the A264K mutant, this is the first report of a Cys-Fe-Lys near-IR MCD band. Crystal structure determination showed that substrate-free A264H and A264K proteins crystallize in distinct conformations, as observed previously in substrate-free and fatty acid-bound wild-type P450 forms, respectively. This, in turn, likely reflects the positioning of the I α helix section of the protein that is required for optimal configuration of the ligands to the heme iron. One of the monomers in the asymmetric unit of the A264H crystals was in a novel conformation with a more open substrate access route to the active site. The same species was isolated for the wild-type heme domain and represents a novel conformational state of BM3 (termed SF2). The "locking" of these distinct conformations is evident from the fact that the endogenous ligands cannot be displaced by substrate or exogenous ligands. The consequent reduction of heme domain conformational heterogeneity will be important in attempts to determine atomic structure of the full-length, multidomain flavocytochrome, and thus to understand in atomic detail interactions between its heme and reductase domains. © 2007 by The American Society for Biochemistry and Molecular Biology, Inc.
    Original languageEnglish
    Pages (from-to)564-572
    Number of pages8
    JournalJournal of Biological Chemistry
    Volume282
    Issue number1
    DOIs
    Publication statusPublished - 5 Jan 2007

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