title: Enhanced enzymatic activity through photoreversible conformational changes.
abstract: The interaction of a light-responsive surfactant with lysozyme at pH 5.0 has been investigated as a means to control protein structure and enzymatic activity with light illumination. The cationic azobenzene surfactant undergoes a reversible photoisomerization upon exposure to the appropriate wavelength of light, with the visible-light (trans) form being more hydrophobic and, thus, inducing a greater degree of protein unfolding than the UV-light (cis) form. Conformational changes as a function of photoresponsive surfactant concentration and light illumination were measured through shape-reconstruction analysis of small-angle neutron scattering (SANS) data. The SANS-based in vitro structures indicate that lysozyme transitions from a nativelike structure at low surfactant concentration to a partially unfolded conformation at higher surfactant concentrations under visible light illumination, while UV-light illumination causes the protein to refold to a near-native structure. Protein swelling occurs principally away from the active site near the hinge region connecting the alpha and beta domains, leading to an increase in the observed separation distance of the alpha and beta domains in the ensemble SANS measurements, a likely result of enhanced domain motions and increased flexibility within the protein. This swelling of the hinge region is accompanied by an 8-fold increase in enzymatic activity relative to the native state. Both enzyme swelling and superactivity observed under visible light can be reversed to nativelike conditions upon exposure to UV light, leading to complete photoreversible control of the structure and function of lysozyme.
authors.affiliation: Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, USA. shaochuw@usc.edu
authors.forename: Shao-Chun
authors.initials: SC
authors.lastname: Wang
authors.forename: C Ted
authors.initials: CT
authors.lastname: Lee
mesh_terms: D000818:Animals; D001391:Azo Compounds / Q000737:chemistry; D002686:Chitin / Q000031:analogs & derivatives / Q000737:chemistry; D004789:Enzyme Activation / Q000528:radiation effects; D006863:Hydrogen-Ion Concentration; D008027:Light; D015394:Molecular Structure; D009113:Muramidase / Q000737:chemistry* / Q000378:metabolism*; D010777:Photochemistry; D011487:Protein Conformation / Q000528:radiation effects; D013501:Surface-Active Agents / Q000737:chemistry; D014466:Ultraviolet Rays
chemical_list: D001391:Azo Compounds; D013501:Surface-Active Agents; D002686:Chitin; C031610:glycolchitin; D009113:Muramidase; C009850:azobenzene