Sulfotransferase (ST) catalyzed sulfation is an important pathway in the metabolism of hydroxyl (aryl or alkyl) containing drugs, carcinogens, xenobiotics and endogenous compounds. Sulfation of drugs and xenobiotics is mostly associated with detoxification by which a relatively hydrophobic compound is biotransformed into a more water-soluble sulfuric ester that is readily excreted. However, there are numerous important exceptions wherein the formation of chemically reactive sulfuric esters is an essential step in metabolic pathways leading to toxic or carcinogenic bioactivation. Detoxification or bioactivation is highly dependent upon the electrophilic reactivity of the individual sulfuric ester products formed. The long-term objective of the proposed research is to define the structural characteristics of the active sites of human STs and to investigate the catalytic mechanism of the sulfation reaction catalyzed by STs. An enzyme's catalytic mechanism and substrate specificity are determined by the micro-environment produced by specific amino acid residues localized within the active site and by the three dimensional structure of the protein molecule. According to our previous studies and reports in the literature, we hypothesize that the co-substrate PAPS binding site is composed of three highly conserved regions and other elements, and the substrate specificity of different STs is dictated by amino acid residues in several variable regions. Specific investigations to be carried out in this proposal are as follows: 1. Use photoaffinity probes to identify amino acid residues in both the substrate- binding site and PAPS binding site of human liver phenol- sulfating ST (P-PST-1), dehydroepiandrosterone ST (DHEA-ST), and estrogen ST (EST). 2. Use amino acid modification reagents to identify the essential amino acid residues in the catalytic active site of STs. 3. Mutagenesis of essential amino acids and/or functional domains of human STs. 4.Computational molecular structure studies of human STs. The computational molecular structure studies, combining the experimental results from specific aims 1-3, will help us to understand the catalytic mechanism and differing substrate specificity of human STs. The information on human ST active site structure, substrate specificity, and catalytic mechanism should have important implications for the prediction of biotransformation pathways and inter-individual differences in metabolism of endogenous compounds, xenobiotics, and carcinogens. The characterization of the active sites of STs will also help to find mechanism-based specific inhibitors/activators for use in studying the physiological functions of STs and designing new drugs.
| Huang, C; Chen, Y; Zhou, T et al. (2009) Sulfation of dietary flavonoids by human sulfotransferases. Xenobiotica 39:312-22 |
| Tyapochkin, Eduard; Cook, Paul F; Chen, Guangping (2008) Isotope exchange at equilibrium indicates a steady state ordered kinetic mechanism for human sulfotransferase. Biochemistry 47:11894-9 |
| Chen, Xinrong; Zhang, Jimei; Baker, Sharon M et al. (2007) Human constitutive androstane receptor mediated methotrexate induction of human dehydroepiandrosterone sulfotransferase (hSULT2A1). Toxicology 231:224-33 |
| Maiti, Smarajit; Zhang, Jimei; Chen, Guangping (2007) Redox regulation of human estrogen sulfotransferase (hSULT1E1). Biochem Pharmacol 73:1474-81 |
| Chen, Xinrong; Maiti, Smarajit; Zhang, Jimei et al. (2006) Nuclear receptor interactions in methotrexate induction of human dehydroepiandrosterone sulfotransferase (hSULT2A1). J Biochem Mol Toxicol 20:309-17 |
| Maiti, Smarajit; Dutta, Sangita Maiti; Baker, Sharon M et al. (2005) In vivo and in vitro oxidative regulation of rat aryl sulfotransferase IV (AST IV). J Biochem Mol Toxicol 19:109-18 |
| Chen, Xinrong; Baker, Sharon M; Chen, Guangping (2005) Methotrexate induction of human sulfotransferases in Hep G2 and Caco-2 cells. J Appl Toxicol 25:354-60 |
| Maiti, Smarajit; Chen, Xinrong; Chen, Guangping (2005) All-trans retinoic acid induction of sulfotransferases. Basic Clin Pharmacol Toxicol 96:44-53 |
| Maiti, Smarajit; Grant, Shannon; Baker, Sharon M et al. (2004) Stress regulation of sulfotransferases in male rat liver. Biochem Biophys Res Commun 323:235-41 |
| Chen, Guangping (2004) Histidine residues in human phenol sulfotransferases. Biochem Pharmacol 67:1355-61 |
Showing the most recent 10 out of 15 publications
