Biotinylating is the process of covalently attaching biotin to a protein. There are two ways of covalently attaching biotin to a protein, one is through biotinylate the protein expressed with avidin tag. The biotin will be conjugated to the N terminal or C terminal. The other way is to biotinylate the protein directly and the biotin will be conjugated to the primary amines. Biotinylating is rapid, specific and is unlikely to disturb the natural function of the molecule due to the small size of biotin. The binding of biotin with streptavidin or avidin is extremely strong, which is used widely in protein biochemistry.