ИСТИНА

Cysteine synthase A (CysK) is an enzyme that catalyzes synthesis of L-cysteine from O-acetyl-L-serine and sulfide (primarily hydrogen sulfide) with PLP as cofactor. While its primary role in cysteine biosynthesis and sulfur assimilation is important for living organisms this enzyme also has potential secondary (or moonlighting) functions such as regulation of various gene expression by binding to DNA or RNA, cellular signaling by varying cysteine levels, or even affecting apoptosis and its pathways by differentiating in cysteine levels which is needed for glutathione synthesis necessary for protection from apoptosis induced by oxidation stress. One such CysK was found in Limosilactobacillus reuteri LR1 where it was expressed only in response to Klebsiella pneumoniae presence. In this work, the recombinant enzyme CysK from L. reuteri LR1 (the strain was kindly provided by the All-Russian Dairy Research Institute (VNIMI)) was obtained and its various properties were studied. The enzymatic activity of this CysK was studied using several different methods such as spectrophotometry and hydrophilic interactions liquid chromatography (HILIC) and the results were compared. Using the most efficient of these methods, kinetics and stability of this enzyme were also studied. Catalytically important amino acid residues were described using the model structure of this enzyme which was compared to other known structures of CysK from different organisms. The work was supported by the Russian Science Foundation grant No. 23-64-10029.