REVIEW: Cysteine Synthase: A Key Enzyme of Cysteine Biosynthetic Pathway

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Evgenii K. Les^1,2, Evgenii V. Pometun³, Svyatoslav S. Savin^1,2, Vladimir I. Tishkov^1,2, and Anastasia A. Pometun^1,4,a*

¹Research Center for Fundamental Biotechnology, Bach Institute of Biochemistry, Russian Academy of Sciences, 119071 Moscow, Russia

²Faculty of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia

³Federal State Autonomous Educational Institution of Higher Education I.M. Sechenov First Moscow State Medical University of the Ministry of Health of the Russian Federation (Sechenov University), 119048 Moscow, Russia

⁴Institute of Medicine, Peoples’ Friendship University of Russia named after Patrice Lumumba, 117198 Moscow, Russia

^* To whom correspondence should be addressed.

Received: July 9, 2025; Revised: October 2, 2025; Accepted: October 3, 2025

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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.

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KEY WORDS: cysteine, cysteine synthase, spatial structure, application of cysteine synthase

DOI: 10.1134/S0006297925602084

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