Light activatable antibodies: Models for remotely activatable proteins

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Abstract
The ability to activate biological macromolecules remotely, at specific locations and times, will allow the manipulation of a wide range of cellular activities and give rise to many practical applications. Interest has been shown in the theoretical possibility of accomplishing this by means of photochemical approaches1. Photochemical changes of the guest–binding cavity of cyclodextrins has been suggested2; however, these changes require organic solvent. What is needed is a widely and readily applicable method allowing activation under physiological conditions. We have developed such a method. This is based on our demonstration that relatively large amounts of the a–methyl substituted 2–nitrobenzyl alcohol, namely, 1–(2–nitrophenyl)ethanol (NPE) can be coupled to proteins using diphosgene3,4. Previous work involved “caging” of small molecules such as ATP (ref. 5–9) and blocking amino acids10 in peptide synthesis11,12 with 2–nitrobenzyl compounds. For large molecules, site–specific reversible inactivation of T4–lysozyme has been reported following introduction of an aspartyl β–nibenzyl ester into its active site by mutagenesis13. In contrast, the present simple procedure allows an existing protein to be deactivated and then, when and where required, reactivated by exposure to ultraviolet–A (UV–A) light. We have employed antibodies as models for both receptors and ligands and have successfully modulated: antibody binding sites for antigen; antigen binding sites for antibody, and antibody Fc binding sites for Protein A.