CysteineSeitekette

CysteineSeitekette, abbreviated CSEK, is a small cysteine‑rich protein identified in the halophilic archaeon Haloferax volcanii. The protein was first reported in 2019 during a high‑throughput screen for proteins upregulated under oxidative stress. CSEK is encoded by the gene HVO_1692 and consists of 150 amino acids, featuring a characteristic Cys‑X‑2–3‑Cys motif and a potential Zn‑binding domain. Structural predictions based on homology modeling suggest that CSEK adopts a compact, disulfide‑rich fold similar to the thioredoxin domain, with an additional β‑sheet layer that may mediate protein–protein interactions.

Functional studies using gene knockout mutants revealed that loss of CSEK decreases cellular tolerance to high sodium chloride concentrations, indicating a role in osmoregulation. Biochemical assays show that CSEK can scavenge reactive oxygen species, acting as a peroxiredoxin‑like peroxidase. In vitro, purified CSEK reduces hydrogen peroxide with a k_cat of approximately 120 min–1 and a K_M of 30 µM. The protein’s activity is enhanced in the presence of a metal ion cofactor, likely zinc, which is coordinated by four cysteine residues, supporting the proposed Zn‑binding site.

CSEK has attracted interest for biotechnological applications, such as engineering salt‑tolerant crops or developing antioxidant enzymes for industrial processes. However, its exact mechanistic role in vivo remains under investigation, with ongoing studies focusing on its interaction partners and regulatory pathways. Current literature cites a series of papers in the Journal of Molecular Microbiology and the Proceedings of the National Academy of Sciences that describe the biochemical characterization and ecological significance of this protein.