Organization of cytochrome P450 system components in the endoplasmic reticulum (1064.8)

Abstract

Cytochromes P450 (P450s) are membrane‐bound proteins mainly found in the endoplasmic reticulum (ER). The ER membrane is heterogeneous, containing ordered (OD) and disordered domains (DD). These OD are more tightly packed and not readily solubilized with non‐ionic detergent, and are called detergent‐resistant membranes. Recently, our lab showed that CYP1A2 and CPR localize in OD. In this study, we examined the organization of other P450s in rabbit liver microsomes by Brij98 treatment and sucrose gradient centrifugation. Interestingly, CYP2E1 localized in DD and CYP2B4 was equally distributed between the OD and DD. Cholesterol depletion disturbed the distribution of OD‐localized CYP1A2, CYP2B4 and CPR. However, CYP2E1 localization was cholesterol independent. Lastly, to test if P450 localization is a property of the P450, P450 was incorporated into reconstituted systems, consisting of 1) phosphatidylcholine (PC) and 2) lipids mimicking the ER, forming both OD and DD. In PC vesicles both CYP2B4 and CYP2E1 proteins localized in late DD fractions. However, in ER mimicking vesicles, CYP2B4 was found in both OD and DD, whereas CYP2E1 distributed exclusively into DD, consistent with microsomal data. These data demonstrate that P450 system enzymes are organized in specific membrane regions, and the distribution is dependent on the specific P450 being examined. Supported by R01 ES004344 and P42 ES013648