Hapten-directed spontaneous disulfide shuffling: a universal technology for site-directed covalent coupling of payloads to antibodies.

A mutated antibody with a Cys residue substitution at a non-contact position in the heavy chain (K52bC; Kabat numbering) bound the epitope coupled to the fluoroprobe Cy5. Introduction of a Cys residue between the hapten epitope and Cy5 allowed the fluorescent epitope to become covalently linked to the mutated antibody.