Patent ID: 8383425

Claim:
A labeled protein obtained by the steps comprising: a) contacting a post-translationally modified protein comprising an O-GlcNAc pendent moiety with a glycosyl transferase enzyme and a labeling agent having the formula wherein R is a chemical handle selected from the group consisting of straight chain or branched C 1 -C 12 carbon chain bearing a carbonyl group, straight chain or branched C 1 -C 12 carbon chain bearing an azide group, and straight chain or branched C 1 -C 12 carbon chain bearing an alkyne; wherein the carbonyl group, azide group or alkyne is attached to a carbon atom of the carbon chain which is at least one carbon atom removed from the carbon atom of the carbon chain which is attached to the carbon atom of the galactosyl moiety; and wherein the glycosyl transferase is GalT or a mutant of GalT, which catalyzes the transfer of the galactosyl group containing the chemical handle from the labeling agent to the O-GlcNAc pendent moiety on the post-translationally modified protein to provide a post-translationally modified protein linked to the galactosyl moiety containing the chemical handle; and b) contacting the post-translationally modified protein linked to the galactosyl moiety containing the chemical handle obtained in step a) with a detection agent having a reactive group capable of reacting with the chemical handle, wherein the reactive group of the detection agent reacts with the chemical handle to form a covalent bond to obtain said labeled protein.