This symposium summary, sponsored by the ASPET, was held at Experimental Biology 2015 on March 29th in Boston MA. The symposium focused on (1) the interactions of P450s with their redox partners, and (2) the role of the lipid membrane in their orientation and stabilization. Two presentations discussed the interactions of P450s with NADPH-cytochrome P450 reductase (CPR) and cytochrome b5. First, solution NMR was used to compare the protein interactions that facilitated either the hydroxylase or lyase activities of CYP17A1. The lyase interaction was stimulated by the presence of b5 and 17α-hydroxypregnenolone, whereas the hydroxylase reaction was predominant in the absence of b5. The role of b5 was also shown in vivo by selective hepatic knockout of b5 from mice expressing CYP3A4 and CYP2D6 - the lack of b5 caused a decrease in the clearance of several substrates. The role of the membrane on P450 orientation was examined using computational methodologies, showing that the proximal region of the P450 molecule faced the aqueous phase. The distal region, containing the substrate-access channel, was associated with the membrane. The interaction of CPR with the membrane was also described, showing the ability of CPR to "helicopter" above the membrane. Finally, the endoplasmic reticulum (ER) was shown to be heterogeneous, having ordered membrane regions containing cholesterol and more disordered regions. Interestingly, two closely-related CYPs, CYP1A1 and CYP1A2 resided in different regions of the ER. The structural characteristics of their localization were examined. These studies emphasize the importance of P450 protein organization to their function.
- animal models
- cytochrome b5
- enzyme mechanism
- enzyme structure
- membrane-protein interactions
- NADPH cytochrome P450 reductase
- protein-protein interactions