Extensive protein interactions involving cytochrome P450 3A4: a possible contributor to the formation of a metabolosome

Cytochrome P450 (CYP) 3A4 is a membrane protein that catalyzes hydroxylation of endogenous and exogenous substrates. Protein–protein interaction is a crucial factor that regulates the function of enzymes. However, protein–protein interactions involving human CYPs have not been fully understood. In this study, extensive protein–protein interactions involving CYP3A4 were determined by a shotgun analysis of immunoprecipitate utilizing anti-CYP3A4 antibody. Our shotgun analysis revealed that 149 proteins were immunoprecipitated with anti-CYP3A4 antibody in human liver microsomes. We further determined that 51 proteins of 149 proteins were specifically immunoprecipitated with the anti-CYP3A4 antibody. Our analysis demonstrated that other CYP isoforms are interacting with CYP3A4, which is in agreement with previous findings. Based on our current and previous findings, we propose that drug-metabolizing enzymes such as CYP3A4 and UDP-glucuronosyltransferase 2B7 form a metabolosome, which is a functional unit of metabolism consisting of multiple metabolism-related proteins.