Semi-reversible cross-linking. Synthesis and application of a novel heterobifunctional reagent

The synthesis of a novel heterobifunctional cross-linking reagent, 3-(4-azido-2-nitrobenzoylseleno)propionic acid is described. The selenol ester function serves as a selective and reversible thiol reagent. Cross-linking is carried out photochemically via nitrene generation. The reagent is well suited for the identification of the environment of a defined cysteine residue according to the principle of semi-reversible cross-linking (Trommer, W.E., Friebel, K., Kiltz, H.-H. & Kolkenbrock. H. (1977) Adv. Exp. Med. Biol. 86A, 187-195). Cleavage of the thiol ester bond (the first anchor point) can be achieved by a variety of labels carrying an amino function thus giving rise to labelled amino acids or proteins in a distance of about 0.7 nm from the known cysteine residue. Optimal conditions were determined by reaction of 3-(4-azido-2-nitrobenzoylseleno)propionic acid and of its unsubstituted analog with glutathione and N alpha-benzoylglycyllysine. Nucleosidetriphosphate-adenylate kinase from pig muscle was chosen as an example to demonstrate the usefulness of the reagent. 14C-labelled aminobutyric acid was applied to cleave the thiol ester bond between the reagent and cysteine-25 leading to labelling of the N-terminal arginine peptide.