Determination of the sites required for the allosteric inhibition of serine acetyltransferase by L-cysteine in plants.
Serine acetyltransferase (SATase; EC 2.3.1.30) catalyzes the formation of O-acetylserine from L-Ser and acetyl-CoA in plants and bacteria. In plants, two types of SATase have been described. One is allosterically inhibited by L-Cys, and the second is not sensitive to L-Cys inhibition. However, the allosteric site in SATase has not been identified. To understand better the mechanism of L-Cys inhibition of plant SATases, we constructed several chimeric SATase enzymes from watermelon SATase (WaSATase) (sensitive type) and Arabidopsis SAT-p (insensitive type). These enzymes were expressed in Escherichia coli, and inhibition of the mutated SATase activity by L-Cys was analyzed. Mutated WaSATase, in which Met280 was changed to Ile, was no longer inhibited by L-Cys. Analysis of the inhibition the chimeric enzymes indicated that the C-terminal region of WaSATase from Pro276 to Phe285, in which five amino acids are different from those of SAT-p, was responsible for the determination of the sensitivity to L-Cys. In particular, Gly277 in the C-terminal region of WaSATase was primarily responsible for the L-Cys inhibition. The N-terminal half of the protein, which does not contain the catalytic domain, was also important for the sensitivity to L-Cys. These results indicate that the sensitivity of SATase to L-Cys is due to the N-terminal and C-terminal regions rather than to the catalytic domain.
Inoue
K
K
Faculty of Pharmaceutical Sciences, Laboratory of Molecular Biology, Chiba University, Japan.
Noji
M
M
Saito
K
K
D000123:Acetyltransferases / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D017360:Arabidopsis / Q000201:enzymology; D003545:Cysteine / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005246:Feedback; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010940:Plant Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000037:antagonists & inhibitors; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D051050:Serine O-Acetyltransferase
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D000123:Acetyltransferases; D051050:Serine O-Acetyltransferase; D003545:Cysteine