Biomedical subjects

J El Yazal

Publications and source records attributed to J El Yazal.

4 recordsLinked to original sources

PubMed2001

Prediction of organophosphorus acetylcholinesterase inhibition using three-dimensional quantitative structure-activity relationship (3D-QSAR) methods.

Neurotoxic organophosphorous compounds are known to modulate their biological effects through the inhibition of a number of esterases including acetylcholinesterase (AChE), the enzyme responsible for the degradation of the neurotransmitter acetylcholine. In this light, molecular modeling studies were performed on a collection of organophosphorous acetylcholinesterase inhibitors by the combined use of conformational analysis and 3D-QSAR methods to rationalize their inhibitory potencies against the enzyme. The Catalyst program was used to identify the structural features in the group of 8 inhibitors whose IC(50) values ranged from 0.34 nM to 1.2 microM. The 3-D pharmacophore models are characterized by at least one hydrogen bond acceptor site and 2-3 hydrophobic sites and demonstrate very good correlation between the predicted and experimental IC(50) values. Our models can be useful in screening databases of organophosphorous compounds for their neurotoxicity potential via the inhibition of acetylcholinesterase. Also, the pharmacophores offer an additional means of designing AChE inhibitors as potential therapeutic agents for central nervous system diseases.

Algorithms↗

PubMed2000

Predicted Michaelis-Menten complexes of cocaine-butyrylcholinesterase. Engineering effective butyrylcholinesterase mutants for cocaine detoxication.

Butyrylcholinesterase (BChE) is important in cocaine metabolism, but it hydrolyzes (-)-cocaine only one-two thousandth as fast as the unnatural (+)-stereoisomer. A starting point in engineering BChE mutants that rapidly clear cocaine from the bloodstream, for overdose treatment, is to elucidate structural factors underlying the stereochemical difference in catalysis. Here, we report two three-dimensional Michaelis-Menten complexes of BChE liganded with natural and unnatural cocaine molecules, respectively, that were derived from molecular modeling and supported by experimental studies. Such complexes revealed that the benzoic ester group of both cocaine stereoisomers must rotate toward the catalytic Ser(198) for hydrolysis. Rotation of (-)-cocaine appears to be hindered by interactions of its phenyl ring with Phe(329) and Trp(430). These interactions do not occur with (+)-cocaine. Because the rate of (-)-cocaine hydrolysis is predicted to be determined mainly by the re-orientation step, it should not be greatly influenced by pH. In fact, measured rates of this reaction were nearly constant over the pH range from 5.5 to 8.5, despite large rate changes in hydrolysis of (+)-cocaine. Our models can explain why BChE hydrolyzes (+)-cocaine faster than (-)-cocaine, and they suggest that mutations of certain residues in the catalytic site could greatly improve catalytic efficiency and the potential for detoxication.

Butyrylcholinesterase↗

PubMed1999

Heterodimeric tacrine-based acetylcholinesterase inhibitors: investigating ligand-peripheral site interactions.

Dimeric acetylcholinesterase (AChE) inhibitors containing a single 9-amino-1,2,3,4-tetrahydroacridine (tacrine) unit were constructed in an effort to further delineate structural requirements for optimal binding to the AChE peripheral site. Basic amines of differing hydrophobicity were selected as peripheral site ligands, and in each case, improvements in inhibitory potency and selectivity were seen relative to tacrine itself. AChE IC(50) values of the optimum dimers decrease significantly as the peripheral site ligand was permuted in the series ammonia > dimethylamine > 4-aminopyridine > 4-aminoquinoline > tacrine. Calculated desolvation free energies of the optimum dimers match the trend in IC(50) values, suggesting the importance of ligand hydrophobicity for effective cation-pi interaction with the peripheral site.

Acetylcholinesterase↗

PubMed1999

Atomic levers control pyranose ring conformations.

Atomic force microscope manipulations of single polysaccharide molecules have recently expanded conformational chemistry to include force-driven transitions between the chair and boat conformers of the pyranose ring structure. We now expand these observations to include chair inversion, a common phenomenon in the conformational chemistry of six-membered ring molecules. We demonstrate that by stretching single pectin molecules (1 --> 4-linked alpha-D-galactouronic acid polymer), we could change the pyranose ring conformation from a chair to a boat and then to an inverted chair in a clearly resolved two-step conversion: 4C1 right arrow over left arrow boat right arrow over left arrow 1C4. The two-step extension of the distance between the glycosidic oxygen atoms O1 and O4 determined by atomic force microscope manipulations is corroborated by ab initio calculations of the increase in length of the residue vector O1O4 on chair inversion. We postulate that this conformational change results from the torque generated by the glycosidic bonds when a force is applied to the pectin molecule. Hence, the glycosidic bonds act as mechanical levers, driving the conformational transitions of the pyranose ring. When the glycosidic bonds are equatorial (e), the torque is zero, causing no conformational change. However, when the glycosidic bond is axial (a), torque is generated, causing a rotation around C---C bonds and a conformational change. This hypothesis readily predicts the number of transitions observed in pyranose monomers with 1a-4a linkages (two), 1a-4e (one), and 1e-4e (none). Our results demonstrate single-molecule mechanochemistry with the capability of resolving complex conformational transitions.

Carbohydrate Conformation↗