Cytosolic Cysteine Synthase Switch Cysteine and Mimosine Production in Leucaena leucocephala
In higher plants, multiple copies of the cysteine synthase gene are present for cysteine biosynthesis. Some of these genes also have the potential to produce various kinds of β-substitute alanine. In the present study, we cloned a 1275-bp cDNA for cytosolic O-acetylserine(thiol)lyase (cysteine synthase) (Cy-OASTL) from Leucaena leucocephala. The purified protein product showed a dual function of cysteine and mimosine synthesis. Kinetics studies showed pH optima of 7.5 and 8.0, while temperature optima of 40 and 35 °C, respectively, for cysteine and mimosine synthesis. The kinetic parameters such as apparent Km, kcat were determined for both cysteine and mimosine synthesis with substrates O-acetylserine (OAS) and Na2S or 3-hydroxy-4-pyridone (3H4P). From the in vitro results with the common substrate OAS, the apparent kcat for Cys production is over sixfold higher than mimosine synthesis and the apparent Km is 3.7 times lower, suggesting Cys synthesis is the favored pathway.
Keywordsα-aminoacrylate β-cyanoalanine synthase β-substituted alanine synthase Cysteine 2,5-dimethyl-3-pyridinol O-acetylserine(thiol)lyase Mimosine
We are grateful to Dr. Shinichi Gima (Instrumental Research Center, University of the Ryukyus) and Dr. Michael Chandro Roy (Okinawa Institute of Science and Technology) for providing technical assistance during LC-MS/MS analyses. We sincerely thank Dr. Rafiq Islam (Professor, Department of Natural Sciences, Northwest Missouri State University) for useful discussion and necessary corrections of our manuscript, and Dr. Steven D. Aird (OIST Graduate University, Okinawa, Japan) for editing the manuscript. The authors also thank Dr. Takeshi Ishikawa (Nagasaki University Graduate School of Biomedical Sciences) for providing us the PAICS program.
M.H.R. and H.I. contributed equally to this work; S.O. performed the molecular dynamics simulation; S.P. performed the experiments, analyzed the data and writing manuscript; F.M. supervised the student, developed the concepts and designed experiments, and edited the manuscript; M.A.H. and T.A. supervised the student; and H.O. supervised the student, performed the molecular dynamics simulation and analysis, and edited the manuscript.
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Conflicts of Interest
The authors declare that they have no conflict of interest.
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