Used in bioconjugation chemistry to modify thiol groups in proteins and peptides. It selectively reacts with cysteine residues, enabling stable linkage formation for labeling, immobilization, or crosslinking applications. Commonly employed in the development of antibody-drug conjugates and functionalized biomaterials. Its NHS ester group couples with primary amines, while the methanethiosulfonate group targets thiols, allowing dual functionality in controlled conjugation strategies. Stable under physiological conditions, it supports use in aqueous buffers and complex biological mixtures.