Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.5.1.47 (cysteine synthase)
 625 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Elevation of glutathione (GSH) is commonly observed in cellular resistance to a number of anticancer agents. Most frequently reported change in GSH metabolism that is associated with the elevated GSH levels is increased mRNA expression and activity of gamma-glutamyl cysteine synthetase (gamma GCS), the first enzyme of the GSH biosynthetic pathway. We have isolated sublines of the A2780 ovarian carcinoma cell line (C10 and C25) that are 8- and 12-fold resistant to oxaliplatin by repeatedly exposing the cells to increasing concentrations of the platinum agent. The GSH levels in C10 and C25 cell sublines are 3.1- and 3.8-fold higher than the parent A2780 cell line. The mRNA levels and activities for gamma GCS and that for gamma-glutamyl transpeptidase (gamma GT), the GSH salvage pathway enzyme, were measured in these cells. The mRNA for gamma GT and gamma GCS were measured by RT-PCR, with quantitation of the PCR product by HPLC; mRNA levels are expressed as ratios to beta-actin mRNA, used as an endogenous standard. GSH and gamma GCS activity were measured by HPLC assays and gamma GT activity by a colorimetric assay. The increase in GSH in C10 and C25 was associated with an elevation in gamma GT mRNA (2.5- and 8-fold) and gamma GT activity (2.7- and 2.8-fold). No changes were observed in gamma GCS mRNA levels or activity. The data indicate that alterations in GSH metabolism leading to elevations in cellular GSH in A2780 ovarian carcinoma cells selected for low levels of resistance to oxaliplatin are mediated by gamma GT, the "salvage' pathway, rather than an increase in GSH biosynthesis.
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PMID:Altered glutathione metabolism in oxaliplatin resistant ovarian carcinoma cells. 868 32

In plants, association of O-acetylserine sulfhydrylase (OASS) and Ser acetyltransferase (SAT) into the Cys synthase complex plays a regulatory role in sulfur assimilation and Cys biosynthesis. We determined the crystal structure of Arabidopsis thaliana OASS (At-OASS) bound with a peptide corresponding to the C-terminal 10 residues of Arabidopsis SAT (C10 peptide) at 2.9-A resolution. Hydrogen bonding interactions with key active site residues (Thr-74, Ser-75, and Gln-147) lock the C10 peptide in the binding site. C10 peptide binding blocks access to OASS catalytic residues, explaining how complex formation downregulates OASS activity. Comparison with bacterial OASS suggests that structural plasticity in the active site allows binding of SAT C termini with dissimilar sequences at structurally similar OASS active sites. Calorimetric analysis of the effect of active site mutations (T74S, S75A, S75T, and Q147A) demonstrates that these residues are important for C10 peptide binding and that changes at these positions disrupt communication between active sites in the homodimeric enzyme. We also demonstrate that the C-terminal Ile of the C10 peptide is required for molecular recognition by At-OASS. These results provide new insights into the molecular mechanism underlying formation of the Cys synthase complex and provide a structural basis for the biochemical regulation of Cys biosynthesis in plants.
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PMID:Structural basis for interaction of O-acetylserine sulfhydrylase and serine acetyltransferase in the Arabidopsis cysteine synthase complex. 1719 64

Cysteine biosynthesis in plants is partly regulated by the physical association of O-acetylserine sulfhydrylase (OASS) and serine acetyltransferase (SAT). Interaction of OASS and SAT requires only the 10 C-terminal residues of SAT. Here we analyze the thermodynamics of formation of a complex of Arabidopsis thaliana OASS (AtOASS) and the C-terminal ligand of AtSAT (C10 peptide) as a function of temperature and salt concentration using fluorescence spectroscopy and isothermal titration calorimetry (ITC). Our results suggest that the C-terminus of AtSAT provides the major contribution to the total binding energy in the plant cysteine synthase complex. The C10 peptide binds to the AtOASS homodimer in a 2:1 complex. Interaction between AtOASS and the C10 peptide is tight (Kd = 5-100 nM) over a range of temperatures (10-35 degrees C) and NaCl concentrations (0.02-1.3 M). AtOASS binding of the C10 peptide displays negative cooperativity at higher temperatures. ITC studies reveal compensating changes in the enthalpy and entropy of binding that also depend on temperature. The enthalpy of interaction has a significant temperature dependence (DeltaCp = -401 cal mol-1 K-1). The heat capacity change and salt dependence studies suggest that hydrophobic interactions drive formation of the AtOASS.C10 peptide complex. The potential regulatory effect of temperature on the plant cysteine synthase complex is discussed.
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PMID:Thermodynamics of the interaction between O-acetylserine sulfhydrylase and the C-terminus of serine acetyltransferase. 1742 33