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Mechanistic insight of photo‐induced aggregation of chicken egg white lysozyme: The interplay between hydrophobic interactions and formation of intermolecular disulfide bonds
Author(s) -
Xie Jinbing,
Qin Meng,
Cao Yi,
Wang Wei
Publication year - 2011
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.23074
Subject(s) - chemistry , hydrophobic effect , circular dichroism , lysozyme , globular protein , protein aggregation , intermolecular force , dynamic light scattering , hydrogen bond , crystallography , protein folding , biophysics , molecule , organic chemistry , nanotechnology , biochemistry , materials science , nanoparticle , biology
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. Proteins 2011; © 2011 Wiley‐Liss, Inc.