Molecular characterization of cytosolic cysteine synthase in Mimosa pudica
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In the cysteine and mimosine biosynthesis process, O-acetyl-l-serine (OAS) is the common substrate. In the presence of O-acetylserine (thiol) lyase (OASTL, cysteine synthase) the reaction of OAS with sulfide produces cysteine, while with 3-hydroxy-4-pyridone (3H4P) produces mimosine. The enzyme OASTL can either catalyze Cys synthesis or both Cys and mimosine. A cDNA for cytosolic OASTL was cloned from M. pudica for the first time containing 1,410 bp nucleotides. The purified protein product from overexpressed bacterial cells produced Cys only, but not mimosine, indicating it is Cys specific. Kinetic studies revealed that pH and temperature optima for Cys production were 6.5 and 50 °C, respectively. The measured Km, Kcat, and Kcat Km−1 values were 159 ± 21 µM, 33.56 s−1, and 211.07 mM−1s−1 for OAS and 252 ± 25 µM, 32.99 s−1, and 130.91 mM−1s−1 for Na2S according to the in vitro Cys assay. The Cy-OASTL of Mimosa pudica is specific to Cys production, although it contains sensory roles in sulfur assimilation and the reduction network in the intracellular environment of M. pudica.
Keywordsα-Aminoacrylate Cysteine 2,5-Dimethyl-3-pyridinol O-acetylserine (thiol) lyase Mimosine
We are grateful to Dr. Shinichi Gima of the Instrumental Research Center, University of the Ryukyus, and Dr. Michael Chandro Roy of the Okinawa Institute of Science and Technology for providing technical assistance during the LC–MS/MS analyses. We sincerely thank to Dr. Rafiq Islam (Professor, Department of Natural Sciences, Northwest Missouri State University) for useful discussion and necessary corrections of our manuscript.
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