Comparative study on cytochrome P-450 of yeasts using specific antibodies to cytochromes P-450alk and P-450(14DM)

A gene from the fungal plant pathogen Nectria haematococca that encodes the phytoalexin-detoxifying enzyme pisatin demethylase defines a new cytochrome P450 family

The gene PDAT9 from the fungus Nectria haematococca encodes pisatin demethylase, an enzyme that detoxifies the phytoalexin pisatin, an antimicrobial compound produced by pea in response to infection by this plant pathogen. PDAT9 was found to contain an open reading frame (ORF) encoding 515 amino acids and four introns of 52-58 nucleotides each within its coding region. The amino acid sequence F-G-A-G-S-R-S-C-I-G, indicative of the "fifth ligand binding site" present in all cytochrome P450s, occurs as residues 446 to 455, confirming that PDAT9 is a cytochrome P450. The deduced amino acid sequence is distinct from all other reported cytochrome P-450s, and PDAT9 has been assigned to a new cytochrome P450 family, CYP57. A 1.3 kb SacI fragment of the PDAT9 ORF that lacked the fifth ligand binding site, hybridized to unique DNA fragments in N. haematococca isolates known to possess PDA genes that encode different whole cell phenotypes for pisatin demethylating activity. These genes were also tentatively identified as cytochrome P450s by the hybridization of the same fragments to separate subclones of PDAT9, one of which contained the fifth ligand sequence. That probe also hybridized to DNA other than that attributed to pisatin demethylase genes; these other DNAs are presumed to represent other cytochrome P450s.

Plant sterol biosynthesis: novel potent and selective inhibitors of cytochrome P450-dependent obtusifoliol 14 alpha-methyl demethylase

The R-(-) isomer of methyl 1-(2,2-dimethylindan-1-yl)imidazole-5-carboxylate (CGA 214372; 2) strongly inhibited P450-dependent obtusifoliol 14 alpha-demethylase (P450OBT.14DM) (I50 = 8 x 10(-9) M, I50/Km = 5 x 10(-5) in a maize (Zea mays) microsomal preparation. Kinetic studies indicated uncompetitive inhibition with respect to obtusifoliol. The corresponding S-(+) isomer was a 20-fold weaker inhibitor for P450OBT.14DM. The molecular features of a variety of analogues of 2 were related to their potency as inhibitors of P450OBT.14DM in vitro, allowing delineation of the key structural requirements governing inhibition of the demethylase. CGA 214372 proved to have a high degree of selectivity for P450OBT.14DM. This allowed easy distinction of this activity from other P450-dependent activities present in the maize microsomal preparation and gave strong evidence that P450OBT.14DM is a herbicidal target. Microsomal maize P450OBT.14DM and yeast P450LAN.14DM, the only known examples of P450-dependent enzymes carrying out an identical metabolic function in different eukaryotes, showed distinct inhibition patterns with CGA 214372 and ketoconazole, a substituted imidazole anti-mycotic.

Maximizing the expression of mammalian cytochrome P-450 monooxygenase activities in yeast cells

Cytochrome P-450s constitute a superfamily of mono-oxygenases which require the association with specific redox enzymes bound to the endoplasmic reticulum membrane for their activity. Conditions for the functional expression of these mammalian enzymes in yeast cells and the respective merits and limitations of currently used P-450 expression systems, are considered. The dependence of the mouse P-450 IA1 specific activity on the cytochrome expression level in yeast microsomes is studied and results demonstrate that the low amounts of endogenous NADPH-cytochrome P-450 reductase and cytochrome b5 which are naturally present, are limiting for the heterologous monooxygenase activities. The sequences encoding human liver cytochrome b5, the native and a modified form of the yeast NADPH-cytochrome P-450 reductase were cloned by making use of PCR techniques, over-expressed in yeast as functional forms, and characterized. New vectors allowing a high level of mammalian P-450 expression upon induction were also constructed and tested. A strategy for the construction of a co-expression system allowing maximal activity of mammalian cytochrome P-450s is discussed.