The long-term objective of this proposal is to elucidate the structural basis for the unique functional properties of cytochromes P450 3A. These enzymes are very versatile catalysts and play a crucial role in the hepatic metabolism of a wide variety of compounds of pharmacological and toxicological interest. P450 3A enzymes are induced or inhibited by numerous foreign compounds and are involved in important drug-drug interactions in humans. In general, the functions of cytochromes P450 3A are conserved within and across species but are distinct from those of P450s from other subfamilies. Most P450 3A enzymes catalyze steroid 6 beta-hydroxylation and macrolide antibiotic metabolism and exhibit stimulation by alpha-naphthoflavone (alpha-NF). Cytochromes P450 3A accommodate some of the largest substrates known for any P450, such as cyclosporin A, and are thought to possess multiple binding sites. However, little information is available, on the structural features of the enzymes that confer their catalytic properties. Building on extensive site-directed mutagenesis and molecular modeling studies from this laboratory on determinants of P450 2B specificity, the current proposal focuses on human P450 3A4 and 3A5. 3A4 is the most highly expressed P450 in the liver of most humans and appears to metabolize more clinically important drugs than any other human P450. P450 3A4 also metabolizes the environmental contaminants benzo(a)pyrene and aflatoxin B1. P450 3A5 is expressed in the liver of approximately one in four individuals. The central hypothesis is that cytochromes P450 3A have structurally distinct substrate binding and effector sites.
The Specific Aims are to: 1) Probe the role of the substrate recognition sites identified in P450 family 2 enzymes in governing the substrate specificity and stimulation by alpha-NF of human P450 3A4 and 3A5; 2) Use random mutagenesis in conjunction with functional screening to identify residues responsible for alpha-NF stimulation of P450 3A4, and probe the biochemical basis of altered flavonoid responsiveness of key cassette, site-directed, and random mutants; 3) Localize the substrate binding and effector sites in 3-D homology models of P450 3A4 and 3A5. Delineation of the structural determinants of human P450 3A activity should aid in predicting drug-drug interactions and lead to improved drug therapy.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM054995-04
Application #
2872717
Study Section
Pharmacology A Study Section (PHRA)
Project Start
1997-02-01
Project End
2001-01-31
Budget Start
1999-02-01
Budget End
2000-01-31
Support Year
4
Fiscal Year
1999
Total Cost
Indirect Cost
Name
University of Texas Medical Br Galveston
Department
Pharmacology
Type
Schools of Medicine
DUNS #
041367053
City
Galveston
State
TX
Country
United States
Zip Code
77555
Davydov, Dmitri R; Yang, Zhongyu; Davydova, Nadezhda et al. (2016) Conformational Mobility in Cytochrome P450 3A4 Explored by Pressure-Perturbation EPR Spectroscopy. Biophys J 110:1485-1498
Davydov, Dmitri R; Davydova, Nadezhda Y; Sineva, Elena V et al. (2015) Interactions among cytochromes P450 in microsomal membranes: oligomerization of cytochromes P450 3A4, 3A5, and 2E1 and its functional consequences. J Biol Chem 290:3850-64
Müller, Christian S; Knehans, Tim; Davydov, Dmitri R et al. (2015) Concurrent cooperativity and substrate inhibition in the epoxidation of carbamazepine by cytochrome P450 3A4 active site mutants inspired by molecular dynamics simulations. Biochemistry 54:711-21
Davydov, Dmitri R; Sineva, Elena V; Davydova, Nadezhda Y et al. (2013) CYP261 enzymes from deep sea bacteria: a clue to conformational heterogeneity in cytochromes P450. Biotechnol Appl Biochem 60:30-40
Sineva, Elena V; Rumfeldt, Jessica A O; Halpert, James R et al. (2013) A large-scale allosteric transition in cytochrome P450 3A4 revealed by luminescence resonance energy transfer (LRET). PLoS One 8:e83898
Davydov, Dmitri R; Davydova, Nadezhda Y; Sineva, Elena V et al. (2013) Pivotal role of P450-P450 interactions in CYP3A4 allostery: the case of ?-naphthoflavone. Biochem J 453:219-30
Davydov, Dmitri R; Rumfeldt, Jessica A O; Sineva, Elena V et al. (2012) Peripheral ligand-binding site in cytochrome P450 3A4 located with fluorescence resonance energy transfer (FRET). J Biol Chem 287:6797-809
Shimshoni, Jakob A; Roberts, Arthur G; Scian, Michele et al. (2012) Stereoselective formation and metabolism of 4-hydroxy-retinoic Acid enantiomers by cytochrome p450 enzymes. J Biol Chem 287:42223-32
Roberts, Arthur G; Yang, Jing; Halpert, James R et al. (2011) The structural basis for homotropic and heterotropic cooperativity of midazolam metabolism by human cytochrome P450 3A4. Biochemistry 50:10804-18
Fernando, Harshica; Rumfeldt, Jessica A O; Davydova, Nadezhda Y et al. (2011) Multiple substrate-binding sites are retained in cytochrome P450 3A4 mutants with decreased cooperativity. Xenobiotica 41:281-9

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