Selective and reversible photochemical derivatization of cysteine residues in peptides and proteins

The selective derivatization of solvent-exposed cysteine residues in peptides and proteins is achieved by brief irradiation of an aqueous solution containing 3-(hydroxymethyl)-2-naphthol derivatives (NQMPs) with a 350 nm fluorescent lamp. NQMP can be conjugated with various moieties, such as PEG, dyes, carbohydrates, or possess a fragment for further selective derivatization, e. g., biotin, azide, alkyne, etc. Attractive features of this labeling approach include an exceptionally fast rate of the reaction and a requirement for a low equivalence of the reagent. The NQMP-thioether linkage is stable under ambient conditions, and survives protein digestion and MS analysis. Irradiation of an NQMP-labeled protein in a dilute solution (<40 mu M) or in the presence of a vinyl ether results in a traceless release of the substrate. The reversible biotinylation of bovine serum albumin, as well as the capture and release of this protein using NeutrAvidin Agarose resin beads has been demonstrated.