Guanidine Hydrochloride Can Induce Amyloid Fibril Formation from Hen Egg-White Lysozyme

Abstract

The formation of amyloid fibrils is an intractable problem in which normally soluble protein polymerizes and forms insoluble ordered aggregates. Such aggregates can range from being a nuisance in vitro to being toxic in vivo. The latter is true for lysozyme, which has been shown to form toxic deposits in humans. In the present study, the effects of partial denaturation of hen egg-white lysozyme via incubation in a concentrated solution of the denaturant guanidine hydrochloride are investigated. Results show that when lysozyme is incubated under moderate guanidine hydrochloride concentrations (i.e., 2-5 M), where lysozyme is partially unfolded, fibrils form rapidly. Thioflavin T, Congo red, X-ray diffraction, transmission electron microscopy, atomic force microscopy, and circular dichroism spectroscopy are all used to verify the production of fibrils under these conditions. Incubation at very low or very high guanidine hydrochloride concentrations fails to produce fibrils. At very low denaturant concentrations, the structure of lysozyme is fully native and very stable. On the other hand, at very high denaturant concentrations, guanidine hydrochloride is capable of dissolving and dis-aggregating fibrils that are formed. Raising the temperature and/or concentration of lysozyme accelerates fibril formation by further adding to the concentration of partially unfolded species. The addition of preformed fibrils also accelerates fibril formation but only under partially unfolding conditions. The results presented here provide further evidence that partial unfolding is a prerequisite to fibril formation. Partial denaturation can accelerate fibril formation in much the same way that mutations have been shown to accelerate fibril formation.