Caging groups for cysteine: Synthesis and biological applications

Photoremovable protecting groups, or caging groups, have been utilized over the last 30 years to study and manipulate biological phenomena. This is accomplished by the covalent attachment of a caging group to a molecule of interest, thereby changing the reactivity and recognition of the functional group to which the covalent bond was attached. However, upon irradiation with light, uncaging, with concomitant release of the desired functional group, occurs. Thus, such protecting groups can be used to control the spatiotemporal activity of biomolecules utilizing light as an orthogonal trigger. Since cysteine residues play important roles in enzymatic catalysis and substrate recognition, caging experiments in which the cysteinyl thiol has been caged have been useful for the study of a wide variety of biological phenomena. Here the protecting groups used to cage cysteine and their applications in biochemical experiments are reviewed.