Isolation and characterization of a cDNA clone from Catharanthus roseus encoding NADPH:cytochrome P‐450 reductase, an enzyme essential for reactions catalysed by cytochrome P‐450 mono‐oxygenases in plants

Abstract

The membrane‐bound flavoprotein NADPH:cytochrome P‐450 (cytochrome c) reductase, that functions in electron transfer to cytochrome P‐450 mono‐oxygenases, was purified from a cell suspension culture of the higher plant Catheranthus roseus. Anti‐serum raised against the purified protein was found to inhibit NADPH:cytochrome c reductase activity as well as the activities of the cytochrome P‐450 enzymes geraniol 10‐hydroxylase and trans‐cinnamate 4‐hydroxylase, which are involved in alkaloid biosynthesis and phenylpropanoid biosynthesis, respectively. Immunoscreening of a C. roseus cDNA expression library resulted in the isolation of a partial NADPH: cytochrome P‐450 reductase cDNA clone, which was identified on the basis of sequence homology with NADPH:cytochrome P‐450 reductases from yeast and animal species. The identity of the cDNA was confirmed by expression in Escherichia coli as a functional protein capable of NADPH‐dependent reduction of cytochrome c and neotetrazolium, two in vitro substrates for the reductase. The N‐terminal sequence of the reductase, which was not present in the cDNA clone, was determined from a genomic NADPH: cytochrome P‐450 reductase clone. It was demonstrated that the reductase probably is encoded by a single copy gene. A sequence comparison of this plant NADPH:cytochrome P‐450 reductase with the corresponding enzymes from yeast and animal species showed that functional domains involved in binding of the cofactors FMN, FAD and NADPH are highly conserved between all kingdoms. In C. roseus cell cultures a rapid increase of the reductase steady state mRNA level was observed after the addition of fungal elicitor preparations that are known to induce cytochrome P‐450‐dependent biosynthetic pathways.