A Unified Model of the GABA(A) Receptor Comprising Agonist and Benzodiazepine Binding Sites.
A Unified Model of the GABA(A) Receptor Comprising Agonist and Benzodiazepine Binding Sites.
Filed under: Drug and Alcohol Rehabilitation
PLoS One. 2013; 8(1): e52323
Bergmann R, Kongsbak K, Sørensen PL, Sander T, Balle T
We present a full-length ?(1)?(2)?(2) GABA receptor model optimized for agonists and benzodiazepine (BZD) allosteric modulators. We propose binding hypotheses for the agonists GABA, muscimol and THIP and for the allosteric modulator diazepam (DZP). The receptor model is primarily based on the glutamate-gated chloride channel (GluCl) from C. elegans and includes additional structural information from the prokaryotic ligand-gated ion channel ELIC in a few regions. Available mutational data of the binding sites are well explained by the model and the proposed ligand binding poses. We suggest a GABA binding mode similar to the binding mode of glutamate in the GluCl X-ray structure. Key interactions are predicted with residues ?(1)R66, ?(2)T202, ?(1)T129, ?(2)E155, ?(2)Y205 and the backbone of ?(2)S156. Muscimol is predicted to bind similarly, however, with minor differences rationalized with quantum mechanical energy calculations. Muscimol key interactions are predicted to be ?(1)R66, ?(2)T202, ?(1)T129, ?(2)E155, ?(2)Y205 and ?(2)F200. Furthermore, we argue that a water molecule could mediate further interactions between muscimol and the backbone of ?(2)S156 and ?(2)Y157. DZP is predicted to bind with interactions comparable to those of the agonists in the orthosteric site. The carbonyl group of DZP is predicted to interact with two threonines ?(1)T206 and ?(2)T142, similar to the acidic moiety of GABA. The chlorine atom of DZP is placed near the important ?(1)H101 and the N-methyl group near ?(1)Y159, ?(1)T206, and ?(1)Y209. We present a binding mode of DZP in which the pending phenyl moiety of DZP is buried in the binding pocket and thus shielded from solvent exposure. Our full length GABA(A) receptor is made available as Model S1.
HubMed – drug
Modulators of ?-Secretase Activity Can Facilitate the Toxic Side-Effects and Pathogenesis of Alzheimer’s Disease.
Filed under: Drug and Alcohol Rehabilitation
PLoS One. 2013; 8(1): e50759
Svedruži? ZM, Popovi? K, Sendula-Jengi? V
Selective modulation of different A? products of an intramembrane protease ?-secretase, could be the most promising strategy for development of effective therapies for Alzheimer’s disease. We describe how different drug-candidates can modulate ?-secretase activity in cells, by studying how DAPT affects changes in ?-secretase activity caused by gradual increase in A? metabolism.A? 1-40 secretion in the presence of DAPT shows biphasic activation-inhibition dose-response curves. The biphasic mechanism is a result of modulation of ?-secretase activity by multiple substrate and inhibitor molecules that can bind to the enzyme simultaneously. The activation is due to an increase in ?-secretase’s kinetic affinity for its substrate, which can make the enzyme increasingly more saturated with otherwise sub-saturating substrate. The noncompetitive inhibition that prevails at the saturating substrate can decrease the maximal activity. The synergistic activation-inhibition effects can drastically reduce ?-secretase’s capacity to process its physiological substrates. This reduction makes the biphasic inhibitors exceptionally prone to the toxic side-effects and potentially pathogenic. Without the modulation, ?-secretase activity on it physiological substrate in cells is only 14% of its maximal activity, and far below the saturation.Presented mechanism can explain why moderate inhibition of ?-secretase cannot lead to effective therapies, the pharmacodynamics of A?-rebound phenomenon, and recent failures of the major drug-candidates such as semagacestat. Novel improved drug-candidates can be prepared from competitive inhibitors that can bind to different sites on ?-secretase simultaneously. Our quantitative analysis of the catalytic capacity can facilitate the future studies of the therapeutic potential of ?-secretase and the pathogenic changes in A? metabolism.
HubMed – drug
4′-Phosphopantetheinyl Transferase PptT, a New Drug Target Required for Mycobacterium tuberculosis Growth and Persistence In Vivo.
Filed under: Drug and Alcohol Rehabilitation
PLoS Pathog. 2012 Dec; 8(12): e1003097
Leblanc C, Prudhomme T, Tabouret G, Ray A, Burbaud S, Cabantous S, Mourey L, Guilhot C, Chalut C
The cell envelope of Mycobacterium tuberculosis, the causative agent of tuberculosis in humans, contains lipids with unusual structures. These lipids play a key role in both virulence and resistance to the various hostile environments encountered by the bacteria during infection. They are synthesized by complex enzymatic systems, including type-I polyketide synthases and type-I and -II fatty acid synthases, which require a post-translational modification to become active. This modification consists of the covalent attachment of the 4′-phosphopantetheine moiety of Coenzyme A catalyzed by phosphopantetheinyl transferases (PPTases). PptT, one of the two PPTases produced by mycobacteria, is involved in post-translational modification of various type-I polyketide synthases required for the formation of both mycolic acids and lipid virulence factors in mycobacteria. Here we identify PptT as a new target for anti-tuberculosis drugs; we address all the critical issues of target validation to demonstrate that PptT can be used to search for new drugs. We confirm that PptT is essential for the growth of M. bovis BCG in vitro and show that it is required for persistence of M. bovis BCG in both infected macrophages and immunodeficient mice. We generated a conditional expression mutant of M. tuberculosis, in which the expression of the pptT gene is tightly regulated by tetracycline derivatives. We used this construct to demonstrate that PptT is required for the replication and survival of the tubercle bacillus during the acute and chronic phases of infection in mice. Finally, we developed a robust and miniaturized assay based on scintillation proximity assay technology to search for inhibitors of PPTases, and especially of PptT, by high-throughput screening. Our various findings indicate that PptT meets the key criteria for being a therapeutic target for the treatment of mycobacterial infections.
HubMed – drug
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