Investigating the role of the microsomal epoxide hydrolase membrane topology and its implication for drug metabolism pathways

Abstract

The microsomal epoxide hydrolase (mEH) catalyzes the hydrolysis of reactive epoxides which are formed by the action of cytochromes P450 from xenobiotics. In addition the mEH has been found to mediate the transport of bile acids. For the mEH it has been shown that it is cotranslationally inserted into the endoplasmic reticulum. Here we demonstrate that the amino- terminal twenty amino acid residues of this protein serve as its single membrane anchor signal sequence and that the function of this sequence can be also supplied by a cytochrome P450 (CYP2B1) anchor signal sequence. In addition we present data showing that she membrane anchor signal sequence of the mEH is dispensable for the catalytic activity of this protein. Our results indicate that it might be feasable to invert the topology of the mEH in the membrane of the endoplasmic reticulum without affecting the catalytic activity of this protein. With this strategy it will be possible to investigate whether the membrane topology of xenobiotic metabolizing enzymes is important for their role in chemical carcinogenesis.