title: Mechanistic insight of photo-induced aggregation of chicken egg white lysozyme: the interplay between hydrophobic interactions and formation of intermolecular disulfide bonds.
abstract: Recently, it was reported that ultraviolet (UV) illumination could trigger the unfolding of proteins by disrupting the buried disulfide bonds. However, the consequence of such unfolding has not been adequately evaluated. Here, we report that unfolded chicken egg white lysozyme (CEWL) triggered by UV illumination can form uniform globular aggregates as confirmed by dynamic light scattering, atomic force microscopy, and transmission electron microscopy. The assembling process of such aggregates was also monitored by several other methods, such as circular dichroism, fluorescence spectroscopy, mass spectrometry based on chymotrypsin digestion, ANS-binding assay, Ellman essay, and SDS-PAGE. Our finding is that due to the dissociation of the native disulfide bonds by UV illumination, CEWL undergoes drastic conformational changes resulting in the exposure of some hydrophobic residues and free thiols. Subsequently, these partially unfolded molecules self-assemble into small granules driven by intermolecular hydrophobic interaction. With longer UV illumination or longer incubation time, these granules can further self-assemble into larger globular aggregates. The combined effects from both the hydrophobic interaction and the formation of intermolecular disulfide bonds dominate this process. Additionally, similar aggregation behavior can also be found in other three typical disulfide-bonded proteins, that is, α-lactalbumin, RNase A, and bovine serum albumin. Thus, we propose that such aggregation behavior might be a general mechanism for some disulfide-bonded proteins under UV irradiation.
authors.affiliation: National Laboratory of Solid State Microstructure, Nanjing University, Nanjing, China.
authors.forename: Jinbing
authors.initials: J
authors.lastname: Xie
authors.forename: Meng
authors.initials: M
authors.lastname: Qin
authors.forename: Yi
authors.initials: Y
authors.lastname: Cao
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
mesh_terms: D000818:Animals; D002645:Chickens; D002942:Circular Dichroism; D004220:Disulfides / Q000737:chemistry* / Q000528:radiation effects; D004527:Egg Proteins / Q000737:chemistry* / Q000648:ultrastructure; D004591:Electrophoresis, Polyacrylamide Gel; D057927:Hydrophobic and Hydrophilic Interactions / Q000528:radiation effects; D008027:Light; D013058:Mass Spectrometry; D018625:Microscopy, Atomic Force; D046529:Microscopy, Electron, Transmission; D009113:Muramidase / Q000737:chemistry* / Q000648:ultrastructure; D017510:Protein Folding / Q000528:radiation effects; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence; D014466:Ultraviolet Rays
chemical_list: D004220:Disulfides; D004527:Egg Proteins; D009113:Muramidase