Human cytosolic sulfotransferases(hSULTs)are important phase II metabolic enzymes[1-3].They catalyze transfer of the sulfuryl-group(-SO3)from 3-phosphoadenosine 5-phosphosulfate(PAPS)to the hydroxyl or primary amine moieties of a large number of endogenous and xenobiotic substrates.Broad selectivity and specificity of binding and activity within the sulfortransferases family could be detected by thermal denaturation assays[4],which have been made more and more suitable for high throughput screening based on recent technical advances[5].Here molecular dynamics simulations were used to explore the effect of the cofactor(PAPS)and substrate(LCA)on the thermal stability of the enzyme.It was found that the apo-enzyme unfolded fastest upon heating.The holo-enzyme with bound substrate LCA unfolded slowest.This thermo-denaturation order is consistent with that observed in experiments.Further it was found that the cofactor and substrate will pronouncedly increase the thermal stability of the active pocket regions that interact directly with the ligands.In addition,cofactor and substrate show noticeable synergy effect on the thermal stability of the enzyme.