Alcohol-inducible cytochrome P-450IIE1 lacking the hydrophobic NH2-terminal segment retains catalytic activity and is membrane-bound when expressed in Escherichia coli

Abstract

We have expressed in Escherichia coli a cDNA encoding rabbit liver cytochrome P-450IIE1, the ethanol-inducible P-450. The expressed P-450 is located primarily in the bacterial inner cell membrane and comprises 3% of the E. coli total membrane protein. The partially purified cytochrome exhibits a reduced CO difference spectrum with a maximum at 452 nm, characteristic of P-450IIE1, and solubilized membranes or partially purified P-450 preparations reconstituted with NADPH-cytochrome P-450 reductase and phosphatidylcholine catalyze the deethylation of N-nitrosodiethylamine with a turnover number equal to that of purified liver P-450IIE1 (approximately 4.5 nmol/min/nmol of P-450). A modified IIE1 cDNA that encodes a protein lacking amino acids 3-29, a proposed membrane anchor for cytochrome P-450, was also expressed in E. coli and, unexpectedly, the shortened protein was also found to be predominantly located in the bacterial inner membrane rather than the cytosol. Like the full-length protein, this truncated cytochrome has a reduced CO difference spectrum characteristic of P-450IIE1 and is fully active in the deethylation of N-nitrosodiethylamine. These results demonstrate that the NH2-terminal hydrophobic segment is not solely responsible for attachment to the membrane and evidently is not required for proper protein folding or catalytic activity.