Reversible control of enzyme‐inhibitor interactions with light illumination using a photoresponsive surfactant

Abstract

The effects of a photoresponsive surfactant and light illumination on the complex formed between ribonuclease A (RNase A) and a protein ribonuclease inhibitor (RI) have been investigated to develop a light‐based technique to reactivate an enzyme through surfactant‐induced dissociation of the enzyme‐inhibitor complex. The photoresponsive surfactant undergoes a photoisomerization from the relatively hydrophobic trans isomer under visible light to the relatively hydrophilic cis isomer upon UV illumination, providing a means to reversibly control protein‐inhibitor interactions. In the absence of surfactant, RI binds tightly to RNase A through noncovalent interactions, which inhibits the enzyme activity. Upon addition of the surfactant under visible light, RNase A is reactivated, regaining ~75% of the native activity in the absence of RI. In the presence of the surfactant under UV light, however, the enzyme remains inhibited. Fluorescence spectroscopy, dynamic light scattering, and circular dichroism spectroscopy reveal that RI dramatically unfolds upon addition of the trans form of the surfactant, while RNase A does not undergo noticeable structural changes under the same conditions. This indicates that RNase A reactivation occurs through dissociation of the enzyme‐inhibitor complex arising from surfactant‐induced unfolding of the inhibitor. As a result, photoresponsive surfactant and light illumination can be used as a novel light‐based technique to dissociate enzyme‐inhibitor complexes and, thus, reactivate an inhibited enzyme.

Enhanced Activity of the Cellulase Enzyme β-Glucosidase upon Addition of an Azobenzene-Based Surfactant

“…Azobenzene trimethylammonium bromide (azoTAB, see Scheme ) is a light-responsive surfactant that undergoes photoisomerization from a relatively hydrophobic trans form under visible light to a relatively hydrophilic cis isomer under UV light. This allows a photoreversible control of surfactant–protein interactions − and thus changes in the secondary, tertiary, and quaternary structures of proteins; , enzyme kinetics, , internal dynamics, and inhibitor interactions; and membrane protein folding . Examples demonstrating increases in enzymatic activity include an azobenzene-conjugated papain (threefold), an RNase S with phenylazophenylalanine (fourfold), a lysozyme with azoTAB (eightfold), and an endonuclease cross-linked to azobenzene (16-fold) .…”