1.6 Å Cytochrome P450 2B4

“Open” conformation with active site heme readily accessible to substrates

The 1.6 Å structure of cytochrome P450 2B4 (1) represented as a ribbons diagram and with the solvent accessible surface (inset). This structure identified a new “open” conformation for mammalian P450s. The overall P450 fold is maintained, but helices B'-C (orange) and F'-G (purple) form an open cleft from solvent directly to the active site on the distal side of the heme prosthetic group (red). Molecular figures were generated with Pymol unless specified otherwise.

1.9 Å Cytochrome P450 2B4(H226Y) + inhibitor

4-(4-chlorophenyl)
Imidazole inhibitor

“Closed” conformation with active site heme inaccessible to substrates

2.8 Å structure of cytochrome P450 2B4 binding the specific inhibitor 4-(4-chlorophenyl)-imidazole (2) represented as a ribbons diagram and with the solvent accessible surface (inset) This structure reveals a “closed” conformation with no route from solvent to the buried heme group (red). Helices B'-C (orange) and F'-G (purple) alter their positions to form the “roof” of the active site. The protein has a single internal mutation, H226A, which is solvent exposed.

Biotransformation Core

Biotransformation is the sum of the processes by which foreign chemicals are altered by the body, and usually serves to enhance their detoxification and elimination. However, biotransformation can also result in bioactivation, which involves the production of reactive metabolites that are more toxic, mutagenic, or carcinogenic than their parent compound(s). The balance between detoxification and bioactivation through oxidative Phase I reactions and conjugative Phase II reactions often determines the ultimate toxicity of a given compound. More recently it has become evident that the pathways for elimination of parent compounds and metabolites through transport (Phase III) also need to be considered. Therefore, knowing the levels, activities, and tissue distribution of biotransformation enzymes and transporters in different species is crucial for understanding the potential health risks upon exposure to foreign chemicals.

Research Highlights

Core Director and Members

G.A. Shakeel Ansari, Ph.D., Director, Biotransformation Research Core, Professor, Department of Biochemistry and Molecular Biology

Yogesh Awasthi, Ph.D., Co-Director, Biotransformation Research Core , Professor, Department of Biochemistry and Molecular Biology

Cornelius Elferink, Ph.D., Member, Biotransformation Research Core , Assistant Professor, Department of Pharmacology and Toxicology

James R. Halpert, Ph.D., Director, NIEHS Center and Member, Biotransformation Research Core , Professor and Chairman, Department of Pharmacology and Toxicology

Bhupendra Kaphalia, Ph.D., Member, Biotransformation Research Core , Associate Professor, Department of Pathology

Lee-Jane Lu, Ph.D., Member, Biotransformation Research Core , Professor, Department of Preventive Medicine & Community Health

Irina Pikuleva, Ph.D., Member, Biotransformation Research Core , Assistant Professor, Department of Pharmacology and Toxicology

Key Words

Aryl Hydrocarbon Receptor, Cytochrome P450, Fatty Acid Ethyl Ester Synthase, Glutathione-S-transferase, Lipid Conjugate, Pancreatitis, Phytoestrogens, Xenobiotic Metabolism and Transport

2005 Publications

Awasthi S, Singhal SS, Yadav S, Singhal J, Drake K, Nadkar A, Zajac E, Wickramarachchi D, Rowe N, Yacoub A, Boor P, Dwivedi S, Dent P, Jarman WE, John, B, Awasthi YC.  2005. RLIP76 is a major determinant of radiation sensitivity.  Cancer Resarch 65(14):1-7.

Awasthi YC, Ansari GAS, Awasthi S.  2005. Phase II: Conjugation Enzymes, Glutathione   Transferases and Transport Systems. Methods in Enzymology. Volume 401:379-409.

Cai P, Kaphalia BS, Ansari GAS. 2005. Methyl palmitate: Inhibitor of phagpcytosis in rat primary Kupffer cells. Toxicololgy 210, 197-204.

Cai P, Khan F, Kaphalia BS, Ansari GAS. 2005. Immunotoxic response of oleic acid anilide and its hydrolysis products in female MRL+/+ mice. J Immunotoxicol. 2. 231-236.

Davydov DR, Botchkareva AE, Davydova NE, and Halpert JR. 2005 Jul. Resolution of two substrate-binding sites in an engineered cytochrome P450eryF bearing a fluorescent probe. Biophys J. 89(1):418-32.

Davydov DR, Fernando H, Baas BJ, Sligar SG, and Halpert JR. 2005 Oct 25. Kinetics of dithionite-dependent reduction of cytochrome P450 3A4: Heterogeneity of the enzyme caused by its oligomerization. Biochemistry 44(42):13902-13913.

Honma W, Li W, Liu H, Scott EE, and Halpert JR. 2005 Mar 1. Functional role of residues in the helix B’ region of cytochrome P450 2B1. Arch Biochem Biophys. 435(1):157-65.

Huang G, Elferink CJ. 2005. Multiple Mechanisms are Involved in Ah Receptor Mediated Cell Cycle Arrest. Mol. Pharmacol. 67:88-96.

Huang Y, Cao S, Nagamani M, Anderson KE, Grady JJ, and Lu L-JW.  2005. Decreased circulating levels of tumor necrosis factor-alpha (TNF-α) in postmenopausal women during consumption of soy containing isoflavones. J Clin Endocrinol Metab 90, 3956-3962.

Khan SH, Kaphalia BS, Ansari GA. 2005 Apr 23. In vitro conjugation of ethanolamine with fatty acids by rat liver subcellular fractions. J Toxicol Environ Health A.;68 (8):667-76.

Kumar S, Chen CS, Waxman, DJ, and Halpert JR. 2005 May 20. Directed evolution of mammalian cytochrome P450 2B1: Mutations outside of the active site enhance the metabolism of several substrates including the anticancer prodrugs cyclophosphamide and ifosfamide.  J Biol Chem. 280(20):19569-75.

Kumar S, Davydov DR, and Halpert JR. 2005 Aug. Role of cytochrome b₅ in modulating peroxide-supported CYP3A4 activity: Evidence for a conformational transition and P450 heterogeneity. Drug Metab Dispos. 33(8):1131-1316.

Li W, Liu H, Scott E, Meyer F, Halpert JR, Luo X, Shen J, and Jiang H. 2005 Jul. Possible pathways of testosterone egress from the active site of cytochrome P450 2B1: A steered molecular dynamics simulation.  Drug Metab Dispos. 33(7):910-19.

Liang, Liang, FQ.,Assadi R,  Morehead P, Awasthi YC, Godley BF.  2005. Enhanced expression of glutathione S-transferase A1-1 protects against oxidative stress in human retinal pigment epithelial cells. Exp. Eye Res. 8:113-119.

Liu T, Zaman W, Kaphalia BS, Ansari GAS, Garofalo RP, Casola A. 2005.  RSV-induced prostaglandin E2 production occurs via cPLA2 activation: Role in viral replication.  Virology 343:12-24.

Mast N, Graham SE, Andersson U, Bjorkhem I, Hill C, Peterson J, Pikuleva I. 2005 Feb 10. Cholesterol binding to cytochrome P450 7A1, a key enzyme in bile acid biosynthesis. Biochem (44):3259-71.

Mast N, Pikuleva I. 2005 Apr 16. A simple and rapid method to measure cholesterol binding to P450s and other proteins. J Lipid Res (46);1561-68.

Nhan S, Anderson KE, Nagamani M, Grady JJ, and Lu L-JW.  2005. Effect of soymilk supplement on urinary F2 isoprostane levels in pre-menopausal women. Nutrition & Caner, 53 (1): 73-81.

Park KT, Mitchell K, Huang G, Elferink CJ. 2005. The Ah Receptor Predisposes Hepatocytes to Fas-Mediated Apoptosis. Mol. Pharmacol. 67:612-622.

Patrick B, Li J, Jeyabal PV, Reddy PM, Yang Y, Sharma R, Sinha M, Luxon B, Zimniak P, Awasthi S, Awasthi YC.  2005. Depletion of 4-hydroxynonenal hGSTA4-transfected HLE B-3 cells results in profound changes in gene expresson.  Biochem. Biophy. Res. Commun. 334(2):425-432.

Stuckler D, Singhal J, Singhal SS, Yadav S, Awasthi YC, Awasthi S. 2005. RLIP76 transports vinorelbine and mediates rrug resistance in non-small cell lung cancer. Cancer Res.65 (3).

Publications Archive

Important Links

NIEHS Annual Report http://www-apps.niehs.nih.gov/centers/Public/res-core/ctr1062-4258.htm