title: Ligand binding to cytochrome P450 3A4 in phospholipid bilayer nanodiscs: the effect of model membranes.
abstract: The membrane-bound protein cytochrome P450 3A4 (CYP3A4) is a major drug-metabolizing enzyme. Most studies of ligand binding by CYP3A4 are currently carried out in solution, in the absence of a model membrane. Therefore, there is little information concerning the membrane effects on CYP3A4 ligand binding behavior. Phospholipid bilayer Nanodiscs are a novel model membrane system derived from high density lipoprotein particles, whose stability, monodispersity, and consistency are ensured by their self-assembly. We explore the energetics of four ligands (6-(p-toluidino)-2-naphthalenesulfonic acid (TNS), alpha-naphthoflavone (ANF), miconazole, and bromocriptine) binding to CYP3A4 incorporated into Nanodiscs. Ligand binding to Nanodiscs was monitored by a combination of environment-sensitive ligand fluorescence and ligand-induced shifts in the fluorescence of tryptophan residues present in the scaffold proteins of Nanodiscs; binding to the CYP3A4 active site was monitored by ligand-induced shifts in the heme Soret band absorbance. The dissociation constants for binding to the active site in CYP3A4-Nanodiscs were 4.0 microm for TNS, 5.8 microm for ANF, 0.45 microm for miconazole, and 0.45 microm for bromocriptine. These values are for CYP3A4 incorporated into a lipid bilayer and are therefore presumably more biologically relevant that those measured using CYP3A4 in solution. In some cases, affinity measurements using CYP3A4 in Nanodiscs differ significantly from solution values. We also studied the equilibrium between ligand binding to CYP3A4 and to the membrane. TNS showed no marked preference for either environment; ANF preferentially bound to the membrane, and miconazole and bromocriptine preferentially bound to the CYP3A4 active site.
authors.affiliation: Department of Medicinal Chemistry, University of Washington, Seattle, Washington 98195.
authors.forename: Abhinav
authors.initials: A
authors.lastname: Nath
authors.affiliation: Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.
authors.forename: Yelena V
authors.initials: YV
authors.lastname: Grinkova
authors.affiliation: Department of Biochemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Sligar
authors.affiliation: Department of Medicinal Chemistry, University of Washington, Seattle, Washington 98195. Electronic address: winky@u.washington.edu.
authors.forename: William M
authors.initials: WM
authors.lastname: Atkins
mesh_terms: D000818:Animals; D001665:Binding Sites; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry*; D004795:Enzyme Stability; D004800:Enzymes, Immobilized / Q000737:chemistry; D006801:Humans; D008024:Ligands; D008051:Lipid Bilayers / Q000737:chemistry*; D008956:Models, Chemical; D049329:Nanostructures / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry; D012995:Solubility; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000737:chemistry
chemical_list: D004800:Enzymes, Immobilized; D008024:Ligands; D008051:Lipid Bilayers; D010743:Phospholipids; D011994:Recombinant Proteins; D014364:Tryptophan; D003577:Cytochrome P-450 Enzyme System; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human