High-affinity binding of fatty acyl-CoAs and peroxisome proliferator-CoA esters to glutathione S-transferasesReport as inadecuate




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Acyl-CoAs are present at high concentrations within the cell, yet are strongly buffered by specific bindingproteins in order to maintain a low intracellular unbound acyl-CoA concentration, compatible with theirmetabolic role, their importance in cell signaling, and as protection from their detergent properties. Thisintracellular regulation may be disrupted by nonmetabolizables acyl-CoA esters of xenobiotics, such asperoxisome proliferators, which are formed at relatively high concentration within the liver cell. The lowmolecular mass acyl-CoA binding protein ACBP and fatty acyl-CoA binding protein FABP have beenproposed as the buffering system for fatty acyl-CoAs. Whether these proteins also bind xenobiotic-CoA is notknown. Here we have identified new liver cytosolic fatty acyl-CoA and xenobiotic-CoA binding sites asglutathione S-transferase GST, using fluorescent polarization and a acyl-etheno-CoA derivative of theperoxisome proliferator nafenopin as ligand. Rat liver GST and human liver recombinant GSTA1-1, GSTP1-1 andGSTM1-1 were used. Only class alpha rat liver GST and human GSTA1-1 bind xenobiotic-CoAs and fattyacyl-CoAs, with Kd values ranging from 200 nm to 5 mm. One mol of acyl-CoA is bound per mol of dimericenzyme, and no metabolization or hydrolysis was observed. Binding results in strong inhibition of rat liver GSTand human recombinant GSTA1-1 IC50 at the nanomolar level for palmitoyl-CoA but not GSTP1-1 andGSTM1-1. Acyl-CoAs do not interact with the GSTA1-1 substrate binding site, but probably with a differentdomain. Results suggest that under increased acyl-CoA concentration, as occurs after exposure to peroxisomeproliferators, acyl-CoA binding to the abundant class alpha GSTs may result in strong inhibition of xenobioticdetoxification. Analysis of the binding properties of GSTs and other acyl-CoA binding proteins suggest thatunder increased acyl-CoA concentration GSTs would be responsible for xenobiotic-CoA binding whereas ACBPwould preferentially bind fatty acyl-CoAs.Nota general

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Author: Silva, Cecilia; - Loyola, Gloria; - Valenzuela, Rodrigo; - García-Huidobro, Tea; - Monasterio Opazo, Octavio; - Bronfman, Miguel

Source: http://repositorio.uchile.cl/



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