Structures of Human Cytochrome P-450 2E1

Abstract

Human microsomal cytochrome P-450 2E1 (CYP2E1) monooxygenates >70 low molecular weight xenobiotic compounds, as well as much larger endogenous fatty acid signaling molecules such as arachidonic acid. In the process, CYP2E1 can generate toxic or carcinogenic compounds, as occurs with acetaminophen overdose, nitrosamines in cigarette smoke, and reactive oxygen species from uncoupled catalysis. Thus, the diverse roles that CYP2E1 has in normal physiology, toxicity, and drug metabolism are related to its ability to metabolize diverse classes of ligands, but the structural basis for this was previously unknown. Structures of human CYP2E1 have been solved to 2.2 Å for an indazole complex and 2.6 Å for a 4-methylpyrazole complex. Both inhibitors bind to the heme iron and hydrogen bond to Thr 303 within the active site. Complementing its small molecular weight substrates, the hydrophobic CYP2E1 active site is the smallest yet observed for a human cytochrome P-450. The CYP2E1 active site also has two adjacent voids: one enclosed above the I helix and the other forming a channel to the protein surface. Minor repositioning of the Phe 478 aromatic ring that separates the active site and access channel would allow the carboxylate of fatty acid substrates to interact with conserved 216 QXXNN 220 residues in the access channel while positioning the hydrocarbon terminus in the active site, consistent with experimentally observed -1 hydroxylation of saturated fatty acids. Thus, these structures provide insights into the ability of CYP2E1 to effectively bind and metabolize both small molecule substrates and fatty acids.Cytochrome P-450 (P-450) 3 is a superfamily of enzymes involved in monooxygenation of both endogenous and exogenous substrates. A subset of these enzymes, including cytochrome P-450 2E1 (CYP2E1), are known for their role in the clearance of drugs and other xenobiotics by introducing or unmasking sites for subsequent conjugation and elimination from the body. From a biochemical standpoint these enzymes are fascinating for the diversity of substrates each xenobioticmetabolizing P-450 can metabolize, yet often with exquisite selectivity in the metabolites generated. Unfortunately, in the process some P-450-mediated metabolism can produce toxic or carcinogenic products. Among cytochrome P-450 enzymes, CYP2E1 is particularly notable for this ability and the resulting toxicity (1). This activity is most substantial in the liver because CYP2E1 comprises over 50% of the hepatic cytochrome P-450 mRNA (2) and 7% of the hepatic cytochrome P-450 protein (3). However, CYP2E1 is also expressed at lower levels in a variety of extrahepatic tissues (4), where it is thought to play a role in the metabolism of important endogenous molecules. CYP2E1 levels and the resulting toxicity varies markedly in response to alcohol consumption (5), diabetes (6), obesity (7), and fasting (8). Thus, the action of CYP2E1 can have a significant influence on human health and drug metabolism.CYP2E1 has been connected with liver toxicity through two ...

Lettuce Costunolide Synthase (CYP71BL2) and Its Homolog (CYP71BL1) from Sunflower Catalyze Distinct Regio- and Stereoselective Hydroxylations in Sesquiterpene Lactone Metabolism

“…To deduce the mechanisms for LsCOS and HaG8H, energyminimized homology models of these two P450s were generated against the human CYP2E1 (35). To analyze these homology models, substrate GAA was positioned in the active site by orienting the C6 and C8 of GAA perpendicular to the center of the heme group for LsCOS and HaG8H, respectively (supplemental Fig.…”

Ubiquitin-dependent Proteasomal Degradation of Human Liver Cytochrome P450 2E1

“…CYP2E1 structural inactivation not only further enhanced the extent of their phosphorylation but also uncovered two additional sites Ser 387 and Thr 431 phosphorylated to a significant extent (Table 3). Inspection of the CYP2E1 crystal structure (71) reveals that many of these residues, particularly those exhibiting the higher phosphorylation extent, are clustered together in distinct patches along the external surface of the protein (Fig. 6).…”

“…6), a protein studded with 29 Lys residues, 6 most of them solvent-accessible (70,71). It has been previously proposed on the basis of a CYP2E1 homology model that two Lys residues (Lys 317 and Lys 324 ) in an evolutionarily highly conserved CYP2E1 Lys 317 -Ala 340 domain were ubiquitinated by the rabbit reticulocyte ubiquitination machinery (98).…”

Mechanism of hepatoprotective action of methionine and composition “Metovitan” against a background of antituberculosis drugs administration to rats

“…Згідно з даними літератури, 65% CYP3А4 може взаємодіяти з цитохромом b 5 , що призводить до конформаційних змін і, як наслідок, до перерозподілу пулу CYP3А4 [30]. Також цито-хром b 5 досить тісно пов'язаний зі стимуляцією активності CYP2Е1 [31][32][33]. Це узгоджується з нашими даними щодо збільшення рівня експресії CYP3А4 та CYP2Е1 за введен-ня комбінації ПТЗ (рис.…”