CYP102A1, originating from Bacillus megaterium, is a highly active enzyme which has attracted much attention because of its potential applicability as a biocatalyst for oxidative reactions. Previously we developed drug-metabolizing mutant CYP102A1 M11 by a combination of site-directed and random mutagenesis. CYP102A1 M11 contains eight mutations, when compared with wild-type CYP102A1, and is able to produce human-relevant metabolites of several pharmaceuticals. In this study, active-site residue 87 of drug-metabolizing mutant CYP102A1 M11 was mutated to all possible natural amino acids to investigate its role in substrate selectivity and regioselectivity. With alkoxyresorufins as substrates, large differences in substrate selectivities and coupling efficiencies were found, dependent on the nature of residue 87. For all combinations of alkoxyresorufins and mutants, extremely fast rates of NADPH oxidation were observed (up to 6,000 min−1). However, the coupling efficiencies were extremely low: even for the substrates showing the highest rates of O-dealkylation, coupling efficiencies were lower than 1%. With testosterone as the substrate, all mutants were able to produce three hydroxytestosterone metabolites, although with different activities and with remarkably different product ratios. The results show that the nature of the amino acid at position 87 has a strong effect on activity and regioselectivity in the drug-metabolizing mutant CYP102A1 M11. Because of the wide substrate selectivity of CYP102A1 M11 when compared with wild-type CYP102A1, this panel of mutants will be useful both as biocatalysts for metabolite production and as model proteins for mechanistic studies on the function of P450s in general.
Crude extracts of the marine hydroid Garveia annulata show potent inhibition of indoleamine 2,3-dioxygenase (IDO). Fractionation of the extract led to the identification of the new polyketides annulin C (1), 2-hydroxygarveatin E (4), garveatin E (5), and garvin C (9). Annulins A (2), B (3), and C (1) were found to be submicromolar inhibitors of IDO.
Cytochrome P450 BM3 from Bacillus megaterium is a monooxygenase with great potential for biotechnological applications. In this paper, we present engineered drug-metabolizing P450 BM3 mutants as a novel tool for regioselective hydroxylation of steroids at position 16β. In particular, we show that by replacing alanine at position 82 with a tryptophan in P450 BM3 mutants M01 and M11, the selectivity toward 16β-hydroxylation for both testosterone and norethisterone was strongly increased. The A82W mutation led to a ≤42-fold increase in V(max) for 16β-hydroxylation of these steroids. Moreover, this mutation improves the coupling efficiency of the enzyme, which might be explained by a more efficient exclusion of water from the active site. The substrate affinity for testosterone increased at least 9-fold in M11 with tryptophan at position 82. A change in the orientation of testosterone in the M11 A82W mutant as compared to the orientation in M11 was observed by T(1) paramagnetic relaxation nuclear magnetic resonance. Testosterone is oriented in M11 with both the A- and D-ring protons closest to the heme iron. Substituting alanine at position 82 with tryptophan results in increased A-ring proton-iron distances, consistent with the relative decrease in the level of A-ring hydroxylation at position 2β.
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Indoleamine 2,3-dioxygenase (IDO) is a tryptophan degradation enzyme that is emerging as an important drug target. IDO is expressed by many human tumors to help them escape immune detection, and it has been implicated in depression and in the formation of senile nuclear cataracts. There is a need for potent and selective IDO inhibitors for use in research and as lead compounds for drug development. We show that expression of human IDO in a Saccharomyces cerevisiae tryptophan auxotroph restricts yeast growth in the presence of low tryptophan concentrations and that inhibition of IDO activity can restore growth. We use this assay to screen for IDO inhibitors in collections of pure chemicals and crude natural extracts. We identify NSC 401366 (imidodicarbonimidic diamide, N-methyl-N'-9-phenanthrenyl-, monohydrochloride) as a potent nonindolic IDO inhibitor (Ki=1.5 +/- 0.2 microM) that is competitive with respect to tryptophan. We also use this assay to identify the active compound caulerpin from a crude algal extract. The yeast growth restoration assay is simple and inexpensive. It combines desirable attributes of cell- and target-based screens and is an attractive tool for chemical biology and drug screening.
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