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Allosteric Modulation (allosteric + modulation)
Selected AbstractsAllosteric modulation of anti-HIV drug and ferric heme binding to human serum albuminFEBS JOURNAL, Issue 24 2005Alessio Bocedi Human serum albumin (HSA), the most prominent protein in plasma, is best known for its exceptional capacity to bind ligands (e.g. heme and drugs). Here, binding of the anti-HIV drugs abacavir, atazanavir, didanosine, efavirenz, emtricitabine, lamivudine, nelfinavir, nevirapine, ritonavir, saquinavir, stavudine, and zidovudine to HSA and ferric heme,HSA is reported. Ferric heme binding to HSA in the absence and presence of anti-HIV drugs was also investigated. The association equilibrium constant and second-order rate constant for the binding of anti-HIV drugs to Sudlow's site I of ferric heme,HSA are lower by one order of magnitude than those for the binding of anti-HIV drugs to HSA. Accordingly, the association equilibrium constant and the second-order rate constant for heme binding to HSA are decreased by one order of magnitude in the presence of anti-HIV drugs. In contrast, the first-order rate constant for ligand dissociation from HSA is insensitive to anti-HIV drugs and ferric heme. These findings represent clear-cut evidence for the allosteric inhibition of anti-HIV drug binding to HSA by the heme. In turn, anti-HIV drugs allosterically impair heme binding to HSA. Therefore, Sudlow's site I and the heme cleft must be functionally linked. [source] Nucleoside transporter and nucleotide vesicular transporter: Two examples of mnemonic regulationDRUG DEVELOPMENT RESEARCH, Issue 1-2 2001Raquel P. Sen Abstract According to their relevant roles in the regulation and availability of extracellular levels of purinergic signals, the nucleoside transporter and the nucleotide vesicular transporter are subject to acute regulation. The plasma membrane nucleoside transporter has been shown to exhibit several regulatory mechanisms, such as regulation by long-term signals, phosphorylation/dephosphorylation processes, and allosteric modulation. The present work reviews studies concerning allosteric modulation of nucleoside and nucleotide vesicular transporters, as the first reported examples of mnemonic behavior in transporter proteins, presenting kinetic and allosteric cooperativity. This fact implies that the protein can exhibit different conformations, each one with specific kinetic parameters. Transport substrates are able to induce slow conformational changes between the different forms of the transporter. This kinetic mechanism can provide several physiological advantages, since it allows strict control of transport capacity by changes in substrate concentrations. This allosteric modulation has been confirmed in several experimental models, the nucleoside transporter in chromaffin and endothelial cells from adrenal medulla and the nucleotide vesicular transporter in the chromaffin cell granules and rat brain synaptic vesicles. Taking into account these considerations, the mnemonic regulation described here could be a widespread mechanism among transporter proteins. Drug Dev. Res. 52:11,21, 2001. © 2001 Wiley-Liss, Inc. [source] Pharmacodynamic Analysis of the Interaction between Tiagabine and Midazolam with an Allosteric Model That Incorporates Signal TransductionEPILEPSIA, Issue 3 2003Daniėl M. Jonker Summary: ,Purpose: The objective of this study was to characterize quantitatively the pharmacodynamic interaction between midazolam (MDL), an allosteric modulator of the ,-aminobutyric acid subtype A (GABAA) receptor, and tiagabine (TGB), an inhibitor of synaptic GABA uptake. Methods: The in vivo concentration,response relation of TGB was determined through pharmacokinetic/pharmacodynamic (PK/PD) modeling. Rats received a single intravenous dose of 10 mg/kg TGB in the absence and the presence of a steady-state plasma concentration of MDL. The EEG response in the 11.5- to 30-Hz frequency band was used as the pharmacodynamic end point. Results: Infusion of MDL resulted in a mean steady-state plasma concentration of 66 ± 3 ng/ml. A significant pharmacokinetic interaction with TGB was observed. MDL inhibited TGB clearance by 20 ± 7 ml/min/kg from the original value of 89 ± 6 ml/min/kg. However, no changes in plasma protein binding of both drugs were observed. The concentration,EEG relation of TGB was described by the sigmoid- Emax model. The pharmacodynamic parameter estimates of TGB were: Emax = 327 ± 10 ,V, EC50 = 392 ± 20 ng/ml, and nH = 3.1 ± 0.3. These values were not significantly different in the presence of MDL. Factors that may explain the lack of synergism were identified by a mechanism-based interaction model that separates the receptor activation from the signal-transduction process. High efficiency of signal transduction and the presence of a baseline response were shown to diminish the degree of synergism. Conclusions: We conclude that the in vivo pharmacodynamic interaction between MDL and TGB is additive rather than synergistic. This strongly suggests that allosteric modulation of the antiseizure activity of a GAT-1 inhibitor by a benzodiazepine does not offer a therapeutic advantage. [source] Positive allosteric modulation of ,7 neuronal nicotinic acetylcholine receptors: lack of cytotoxicity in PC12 cells and rat primary cortical neuronsBRITISH JOURNAL OF PHARMACOLOGY, Issue 8 2009Min Hu Background and purpose:, ,7-Nicotinic acetylcholine receptors (,7 nAChRs) play an important role in cognitive function. Positive allosteric modulators (PAMs) amplify effects of ,7 nAChR agonist and could provide an approach for treatment of cognitive deficits in neuropsychiatric diseases. PAMs can either predominantly affect the apparent peak current response (type I) or increase both the apparent peak current response and duration of channel opening, due to prolonged desensitization (type II). The delay of receptor desensitization by type II PAMs raises the possibility of Ca2+ -induced toxicity through prolonged activation of ,7 nAChRs. The present study addresses whether type I and II PAMs exhibit different cytotoxicity profiles. Experimental approach:, The present studies evaluated cytotoxic effects of type I PAM [N-(4-chlorophenyl)]-,-[(4-chloro-phenyl)-aminomethylene]-3-methyl-5-isoxazoleacet-amide (CCMI) and type II PAM 1-[5-chloro-2,4-dimethoxy-phenyl]-3-[5-methyl-isoxazol-3-yl]-urea (PNU-120596), or 4-[5-(4chloro-phenyl)-2-methyl-3-propionyl-pyrrol-1-yl]-benzenesulphonamide (A-867744). The studies used cultures of PC12 cells and primary cultures of rat cortical neuronal cells. Key results:, Our results showed that neither type I nor type II PAMs had any detrimental effect on cell integrity or cell viability. In particular, type II PAMs did not affect neuron number and neurite outgrowth under conditions when ,7 nAChR activity was measured by Ca2+ influx and extracellular signal-regulated kinases 1 and 2 phosphorylation, following exposure to ,7 nAChR agonists. Conclusions and implications:, This study demonstrated that both type I and type II ,7 nAChR selective PAMs, although exhibiting differential electrophysiological profiles, did not exert cytotoxic effects in cells endogenously expressing ,7 nAChRs. [source] Oleamide is a selective endogenous agonist of rat and human CB1 cannabinoid receptorsBRITISH JOURNAL OF PHARMACOLOGY, Issue 2 2004James D Leggett The ability of the endogenous fatty acid amide, cis -oleamide (ODA), to bind to and activate cannabinoid CB1 and CB2 receptors was investigated. ODA competitively inhibited binding of the nonselective cannabinoid agonist [3H]CP55,940 and the selective CB1 antagonist [3H]SR141716A to rat whole-brain membranes with Ki values of 1.14 ,M (0.52,2.53 ,M, Hill slope=0.80, n=6) and 2.63 ,M (0.62,11.20 ,M, Hill slope=0.92, n=4), respectively. AEA inhibited [3H]CP55,940 binding in rat whole-brain membranes with a Ki of 428 nM (346,510 nM, Hill slope=,1.33, n=3). ODA competitively inhibited [3H]CP55,940 binding in human CB1 (hCB1) cell membranes with a Ki value of 8.13 ,M (4.97,13.32 ,M, n=2). In human CB2 transfected (hCB2) HEK-293T cell membranes, 100 ,M ODA produced only a partial (42.5±7%) inhibition of [3H]CP55,940 binding. ODA stimulated [35S]GTP,S binding in a concentration-dependent manner (EC50=1.64 ,M (0.29,9.32 ,M), R2=0.99, n=4,9), with maximal stimulation of 188±9% of basal at 100 ,M. AEA stimulated [35S]GTP,S binding with an EC50 of 10.43 ,M (4.45,24.42 ,M, R2=1.00, n=3, 195±4% of basal at 300 ,M). Trans -oleamide (trans- ODA) failed to significantly stimulate [35S]GTP,S binding at concentrations up to 100 ,M. ODA (10 ,M)-stimulated [35S]GTP,S binding was reversed by the selective CB1 antagonist SR141716A (IC50=2.11 nM (0.32,13.77 nM), R2=1.00, n=6). The anatomical distribution of ODA-stimulated [35S]GTP,S binding in rat brain sections was indistinguishable from that of HU210. Increases of similar magnitude were observed due to both agonists in the striatum, cortex, hippocampus and cerebellum. ODA (10 ,M) significantly inhibited forskolin-stimulated cyclic AMP (cAMP) accumulation in mouse neuroblastoma N1E 115 cells (P=0.02, n=11). ODA-mediated inhibition was completely reversed by 1 ,M SR141716A (P<0.001, n=11) and was also reversed by pretreatment with 300 ng ml,1 pertussis toxin (P<0.001, n=6). These data demonstrate that ODA is a full cannabinoid CB1 receptor agonist. Therefore, in addition to allosteric modulation of other receptors and possible entourage effects due to fatty acid amide hydrolase inhibition, the effects of ODA may be mediated directly via the CB1 receptor. British Journal of Pharmacology (2004) 141, 253,262. doi:10.1038/sj.bjp.0705607 [source] Binding characteristics of BmK I, an ,-like scorpion neurotoxic polypeptide, on cockroach nerve cord synaptosomesCHEMICAL BIOLOGY & DRUG DESIGN, Issue 4 2000Y.-J. Li Abstract: In this study, the binding characteristics of BmK I, an ,-like neurotoxic polypeptide purified from the venom of the Chinese scorpion Buthus martensi Karsch, were investigated on rat brain and cockroach nerve cord synaptosomes. The results showed that BmK I can bind to a single class of noninteracting binding sites on cockroach nerve cord synaptosomes with medium affinity (Kd = 16.5 ± 4.4 nm) and low binding capacity (Bmax= 1.05 ± 0.23 pmol/mg protein), but lacks specific binding on rat brain synaptosomes. BmK AS, BmK AS-1 (two novel sodium channel-blocking ligands), BmK IT (an excitatory insect-selective toxin) and BmK IT2 (a depressant insect-selective toxin) from the same venom were found to be capable of depressing BmK I binding in cockroach nerve cord synaptosomes, which might be attributed to either allosteric modulation of voltage-gated Na+ channels by these toxic polypeptides or partial overlapping between the receptor binding sites of BmK I and these toxins. This thus supported the notion that ,-like scorpion neurotoxic polypeptides bind to a distinct receptor site on sodium channels, which might be similar to the binding receptor site of ,-type insect toxins, and also related to those of BmK AS type and insect-selective scorpion toxins on insect sodium channels. [source] | ||||||||||