Structural and functional effects of cytochrome b5 interactions with human cytochrome P450 enzymes

Aaron G Bart,Emily E Scott

doi:10.1074/jbc.ra117.000220

Aaron G Bart, Emily E Scott

Open Access

https://doi.org/10.1074/jbc.ra117.000220

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Abstract

The small heme-containing protein cytochrome b5 can facilitate, inhibit, or have no effect on cytochrome P450 catalysis, often in a P450-dependent and substrate-dependent manner that is not well understood. Herein, solution NMR was used to identify b5 residues interacting with different human drug-metabolizing P450 enzymes. NMR results revealed that P450 enzymes bound to either b5 α4-5 (CYP2A6 and CYP2E1) or this region and α2-3 (CYP2D6 and CYP3A4) and suggested variation in the affinity for b5 Mutations of key b5 residues suggest not only that different b5 surfaces are responsible for binding different P450 enzymes, but that these different complexes are relevant to the observed effects on P450 catalysis.

Highlights

The small heme-containing protein cytochrome b5 can facilitate, inhibit, or have no effect on cytochrome P450 catalysis, often in a P450-dependent and substrate-dependent manner that is not well understood
The ability of P450 enzymes to oxidize such substrates requires interaction with a redox partner protein, catalysis can be modulated by interactions with the membrane-bound heme protein cytochrome b5 (b5)
Allosteric modulation of P450 conformation could result in alterations in substrate binding, electron or proton delivery, or coupling of NADPH consumption to metabolite formation [1,2,3]

Summary

Introduction

The small heme-containing protein cytochrome b5 can facilitate, inhibit, or have no effect on cytochrome P450 catalysis, often in a P450-dependent and substrate-dependent manner that is not well understood. As reported previously for CYP17A1 and CYP2B4, titrations of [15N]b5 with increasing concentrations of 2A6(coumarin) result in few chemical shifts, but line broadening occurs and the intensity of most resonances decreases (Fig. 1C), with more marked reductions for specific residues (Fig. 1D).

Results

Conclusion