Protein dynamics and imidazole binding in cytochrome P450 enzymes

Investigating Structural Property Relationships to Enable Repurposing of Pharmaceuticals as Zinc Ionophores

The importance of zinc in biology has gained greater recognition in recent years due to its essential contributions to the function of many endogenous enzymes. Disruption of zinc homeostasis may be useful in treating pathological conditions, such as Alzheimer's, and for antiviral purposes. Despite the growth of knowledge and increased interest in zinc, little is known about the structure and function of zinc ionophores. In this study we analyse the Cambridge Structural Database and solution complexation studies found in the literature to identify key functional groups which may confer zinc ionophorism. Pharmaceuticals, nutraceuticals and amino acids with these functionalities were selected to enable us to explore the translatability of ionophoric activity from in vitro assays to cellular systems. We find that although certain species may complex to zinc in the solid and solution states, and may carry ions across simple membrane systems, this does not necessarily translate into ionophoric activity. We propose that the CSD can help refine key functionalities but that ionophoric activity must be confirmed in cellular systems.

Sub-lethal effects and bioconcentration of the human pharmaceutical clotrimazole in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to characterize biomarker responses, haematological profiles, structural changes and uptake in juvenile rainbow trout exposed to clotrimazole (CLO) at three concentrations (0.01 - [lowest environmentally relevant concentration], 1.0 [highest environmentally relevant concentration] and 10 μg L(-1)) in a semi-static system over a period of 42 days. Antioxidant defence enzymes, which responded to CLO exposure, changed the oxidative stress status of cells, but no differences were observed in lipid peroxidation. Clotrimazole triggered a biphasic response of CYP3A-like activity in liver microsomes, which may indicate a detoxification process in the liver. Histopathological alterations were most pronounced in kidneys and testes in the group exposed to 10 μg L(-1). Structural changes in the kidney included tubulonephrosis and hyaline droplet degeneration in the tubular epithelial cells. The relative proportions of germ cells in testes were changed: The number of spermatozoa was reduced, and the spermatogonia and spermatocytes were increased. The highest CLO concentration was detected in fish liver (3710 ng per gram wet tissue) and kidney (4280 ng per gram wet tissue). Depuration half-life was estimated to be 72, 159, and 682 h in liver, muscle, and kidney, respectively. Taken together, these results provide valuable toxicological data on the effects of CLO on aquatic non-target organisms, which could be useful for further understanding of the potential risks in the real aquatic environment.

Function, diversity, and application of insect juvenile hormone epoxidases (CYP15)

Juvenile hormones (JHs) represent a family of sesquiterpenoid hormones in insects, and they play a key role in regulating development, metamorphosis, and reproduction. The last two steps of the JH biosynthetic pathway, epoxidation and methyl esterification of farnesoic acid to JH, are insect specific, and thus have long been considered a promising target for biorational insecticides. Recently, the enzymes involved in the last two steps have been molecularly identified: JH acid methyltransferase catalyzes the esterification step and the cytochrome P450 CYP15 enzyme catalyzes the epoxidation step. In this review, we describe the recent progress on the characterization of JH biosynthetic enzymes, with special focus on the function and diversity of the CYP15 family. CYP15 genes have evolved lineage-specific substrate specificity and regulatory mechanisms in insects, which appear to be associated with the lineage-specific acquisition of unique JH structure and function. In addition, the lack of CYP15 genes in crustacean (Daphnia pulex) and arachnid (Tetranychus urticae) species, whose genomes have been fully sequenced, may imply that CYP15 enzymes are an evolutionary innovation in insects to use the epoxide forms of methylated farnesoid molecules as their principal JHs. Molecular identification and characterization of CYP15 genes from broad taxa of insects have paved the way to the design of target-specific, biorational anti-JH agents.

Characterizing metabolic inhibition using electrochemical enzyme/DNA biosensors

Studies of metabolic enzyme inhibition are necessary in drug development and toxicity investigations as potential tools to limit or prevent appearance of deleterious metabolites formed, for example, by cytochrome (cyt) P450 enzymes. In this paper, we evaluate the use of enzyme/DNA toxicity biosensors as tools to investigate enzyme inhibition. We have examined DNA damage due to cyt P450cam metabolism of styrene using DNA/enzyme films on pyrolytic graphite (PG) electrodes monitored via Ru(bpy)(3)(2+)-mediated DNA oxidation. Styrene metabolism initiated by hydrogen peroxide was evaluated with and without the inhibitors, imidazole, imidazole-4-acetic acid, and sulconazole (in micromolar range) to monitor DNA damage inhibition. The initial rates of DNA damage decreased with increased inhibitor concentrations. Linear and nonlinear fits of Michaelis-Menten inhibition models were used to determine apparent inhibition constants (K(I)*) for the inhibitors. Elucidation of the best fitting inhibition model was achieved by comparing correlation coefficients and the sum of the square of the errors (SSE) from each inhibition model. Results confirmed the utility of the enzyme/DNA biosensor for metabolic inhibition studies. A simple competitive inhibition model best approximated the data for imidazole, imidazole-4-acetic acid and sulconazole with K(I)* of 268.2, 142.3, and 204.2 microM, respectively.

Spectral resolution of a second binding site for Nile Red on cytochrome P4503A4

Nile Red is sequentially metabolized by cytochrome P4503A4 to the N-monoethyl and N-desethyl products, which typifies the metabolism of many amine containing drugs. Sequential metabolism of a single substrate results in complex kinetics that confound predictive models of drug clearance. As a fluorescent model for drugs which undergo sequential metabolism, Nile Red provides the opportunity to monitor drug-CYP interactions wherein the fluorescent properties of Nile Red could, in principle, be exploited to determine individual rate and equilibrium constants for the individual reactions. Previously, it was shown that Nile Red binds at the active site and fluoresces (K(D) approximately 50nM) with maximum emission at approximately 620nm, but it was unclear whether a red-shifted emission, at approximately 660nm, consisted of only free Nile Red or Nile Red bound at a second site on the protein. Here, equilibrium binding studies, including 'reverse titrations' spanning low ratios of CYP3A4/Nile Red, indicate two binding sites for Nile Red with a contribution to the 'red emission' greater than can be accounted for by free Nile Red. Singular value decomposition affords basis spectra for both spectral components and fits well to the experimentally determined concentration dependence of Nile Red emission. In addition, the red spectral component, with an apparent K(D)=2.2muM, is selectively eliminated by titration with the known allosteric effectors of CYP3A4, alpha-napthoflavone and testosterone. Furthermore, the double mutant L2311F/D214E, previously demonstrated to perturb a peripheral allosteric site, lacks the red-emitting Nile Red binding site, but retains the blue-emitting site. Together these data indicate that a second Nile Red site competes with other effectors of CYP3A4 at a site that results in Nile Red emission at 660nm.