Expression of Bovine Cytochrome P450c21 and Its Fused Enzymes with Yeast NADPH-Cytochrome P450 Reductase inSaccharomyces cerevisiae

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Abstract
Recombinant plasmids for expression of bovine cytochrome P450c21 (pAγ2), both P450c21 and yeast NADPH-cytochrome P450 reductase (pARγ1), P450c21/yeast reductase fused enzymes (pAFγR1, pAFγR2, and pAFγR20), and yeast reductase/P450c21 fused enzymes (pAFRγ1 and pAFRγ2) were constructed by using expression vector pAAH5. The plasmids were each introduced into the yeast Saccharomyces cerevisiae AH22 cells. The recombinant yeast strains AH22/pAγ2 (Y21) and AH22/pARγ1 (Y21R) produced 2–3 × 103 molecules of P450c21 per cell. The cultures of both strains converted progesterone and 17α-hydroxyprogesterone into 11-deoxycorticosterone and 11-deoxycortisol, respectively. The 21-hydroxylase activity per cell of the strain Y21R was about three times higher than that of the strain Y21, probably due to overproduction of yeast reductase. The recombinant yeast strains AH22/pAFγR1 (Y21RF1), AH22/PAFγR2 (Y21RF2), and AH22/pAFγR20 (Y21RF20) produced about 1.1–2.0 × 104 molecules per cell of the corresponding P450c21/yeast reductase fused enzymes. The specific 21-hydroxylase activity toward 17α-hydroxyprogesterone per cell of the strains Y21RF1, Y21RF2, and Y21RF20 was about 21, 28, and 49 times higher than that of the strain Y21, respectively. Thus, the fused enzymes were superior to P450c21 in the specific activity and in the expression level in the yeast. The Km values for 17α-hydroxyprogesterone of P450c21 in the strains Y21 and Y21R, and of the fused enzymes in the strains Y21RF1 and Y21RF2 were 0.29, 0.30, 0.67, and 0.65 μM, respectively. The Vmax values of P450c21 in the strains Y21 and Y21R, and of the fused enzymes in the strains Y21RF1 and Y21RF2 were 28, 124, 151, and 222 moles/min • mole P450c21 or fused enzyme, respectively. These results indicated that the fused enzymes showed lower affinity for the substrate, probably due to structural modification and higher reaction rates through efficient intramolecular electron transfer as compared with those of P450c21. While the strain AH22/pAFRγ2 (YR21F2) produced about 3 × 104 molecules per cell of the reductase/P450c21 fused enzyme, the specific 21-hydroxylase activity of the fused enzyme toward 17α-hydroxyprogesterone was extremely low, suggesting that the structure of the fused enzyme might not be suited for electron transfer in yeast microsomes.

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