Cysteine Synthase: A Key Enzyme of Cysteine Biosynthetic Pathway

Cysteine is an amino acid essential for normal functioning of living organisms. In bacteria and plants, the main mechanism of cysteine synthesis is the thiolation pathway, the second stage of which is catalyzed by either cysteine synthase A (CysK), if the substrate is inorganic sulfide, or cysteine synthase B (CysM), if the substrate is thiosulfate. The crucial role of these enzymes in cysteine synthesis makes them promising targets for antimicrobial agents and new herbicides, and well as possible components of industrial production of cysteine. In addition to their main functions, cysteine synthases show the antimicrobial and antibiofilm activities. The review discusses the physicochemical characteristics of CysK and CysM, their diversity, and potential applications in biotechnology and medicine.