Photoinduced fibrils formation of chicken egg white lysozyme under native conditions

Abstract

Recent findings showed that transiently accessing structurally native-like yet energetically higher conformational states is sufficient to trigger the formation of protein fibrils. Typically, these conformational states are made available through changing solvent conditions or introducing mutations. Here we show a novel way to initialize fibril formation for Chicken egg white lysozyme (CEWL) under native conditions via controlled UV illumination. Through a cassette of tryptophan-based photochemistry, the two terminal disulfide bonds in CEWL can be selectively reduced. The reduced CEWL is then converted to conformational states with the C-terminal fragment floppy upon thermal fluctuation. These states serve as precursors for the fibrillar aggregation. Intriguingly, the CEWL fibrils are stabilized by intermolecular disulfide bonds instead of noncovalent β-sheet structures, distinct from the amyloid-like lysozyme fibrils reported before. Based on the experimental evidences and all-atom molecular dynamics simulation, we proposed a "runaway domain-swapping" model for the structure of the CEWL fibrils, in which each CEWL molecule swaps the C-terminal fragment into the complementary position of the adjacent molecule along the fibrils. We anticipate that this fibrillation mechanism can be extended to many other disulfide-containing proteins. Our study stands for the first example of formation of protein fibrils under native conditions upon UV illumination and poses the potential danger of low UV dose to organisms at the protein level.

Protein folding guides disulfide bond formation

“…Remarkably, our simulations capture the extent of rate changes found in experiments quantitatively, thus establishing the crucial role the β-hairpin plays in enabling to form. More recently, experiments have further illustrated the link between hydrophobic interactions and disulfide bond formation in controlling fibrillar and globular aggregate formation in egg white lysozyme (30,31).…”

Photo-synthesis of protein-based nanoparticles and the application in drug delivery

“…3 [25]. The two disulfide bonds Cys6-Cys127 and Cys30-Cys115 which connect the two termini of CEWL can be selectively reduced through tryptophan-mediated photo-reduction process.…”

“…We found that the unfolding and self-assembly of UV-illuminated proteins can be well controlled by adjusting the illumination time and intensity of UV light. Under different illumination conditions, the diversity of self-assembled nanoparticles can be easily realized from several nanometers to several micrometers, and even the formation of amyloid-like fibrils [23][24][25]. In fact, the sizes of these globular nanoparticles are quite dependent with the exposure of hydrophobic amino acids of illuminated proteins and their stability is dominated by the newly formed intermolecular disulfide bond.…”

Tightening up the structure, lighting up the pathway: application of molecular constraints and light to manipulate protein folding, self-assembly and function

“…Because of its easy incorporation into peptides and proteins, early attempts have explored the utility of using a disulfide as a phototrigger [53]. While these studies showed that disulfides can be cleaved with ultraviolet light (∼270 nm) [54, 55], the free radicals formed upon photoexcitation often undergo ultrafast geminate recombination and are also very reactive, making it a less-than-ideal trigger. Recently, several studies have shown that it is possible to remediate these pitfalls.…”