Molecular cloning of putative chloroplastic cysteine synthase in Leucaena leucocephala

J Plant Res. 2020 Jan;133(1):95-108. doi: 10.1007/s10265-019-01158-y. Epub 2019 Dec 11.


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 α-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 °C. In the cysteine synthesis assay, the Km and kcat values were 838 ± 26 µM and 72.83 s-1 for OAS, respectively, and 60 ± 2 µM 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.

Keywords: 2,5-Dimethyl-3-pyridinol; Active site; Chloroplastic OASTL; Cysteine synthase complex; O-acetylserine (thiol) lyase; α-Aminoacrylate.

MeSH terms

  • Chloroplasts*
  • Cloning, Molecular
  • Cysteine Synthase
  • Kinetics
  • Mimosine


  • Mimosine
  • Cysteine Synthase