Journal
JOURNAL OF PLANT RESEARCH
Volume 133, Issue 1, Pages 95-108Publisher
SPRINGER JAPAN KK
DOI: 10.1007/s10265-019-01158-y
Keywords
alpha-Aminoacrylate; Active site; 2; 5-Dimethyl-3-pyridinol; O-acetylserine (thiol) lyase; Chloroplastic OASTL; Cysteine synthase complex
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Cysteine biosynthesis is directed by the successive commitments of serine acetyltransferase, and O-acetylserine (thiol) lyase (OASTL) compounds, which subsequently frame the decameric cysteine synthase complex. The isoforms of OASTL are found in three compartments of the cell: the cytosol, plastid, and mitochondria. In this investigation, we first isolated putative chloroplastic OASTL (Ch-OASTL) from Leucaena leucocephala, and the Ch-OASTL was then expressed in BL21-competent Escherichia coli. The putative Ch-OASTL cDNA clone had 1,543 base pairs with 391 amino acids in its open reading frame and a molecular weight of 41.54 kDa. The purified protein product exhibited cysteine synthesis ability, but not mimosine synthesis activity. However, they both make the common alpha-aminoacrylate intermediate in their first half reaction scheme with the conventional substrate O-acetyl serine (OAS). Hence, we considered putative Ch-OASTL a cysteine-specific enzyme. Kinetic studies demonstrated that the optimum pH for cysteine synthesis was 7.0, and the optimum temperature was 40 degrees C. In the cysteine synthesis assay, the K-m and k(cat) values were 838 +/- 26 mu M and 72.83 s(-1) for OAS, respectively, and 60 +/- 2 mu M and 2.43 s(-1) for Na2S, respectively. We can infer that putative Ch-OASTL regulatory role is considered a sensor for sulfur constraint conditions, and it acts as a forerunner of various metabolic compound molecules.
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