Sonication of proteins causes formation of aggregates that resemble amyloid

Abstract

Despite the widespread use of sonication in medicine, industry, and research, the effects of sonication on proteins remain poorly characterized. We report that sonication of a range of structurally diverse proteins results in the formation of aggregates that have similarities to amyloid aggregates. The formation of amyloid is associated with, and has been implicated in, causing of a wide range of protein conformational disorders including Alzheimer's disease, Huntington's disease, Parkinson's disease, and prion diseases. The aggregates cause large enhancements in fluorescence of the dye thioflavin T, exhibit green-gold birefringence upon binding the dye Congo red, and cause a red-shift in the absorbance spectrum of Congo red. In addition, circular dichroism reveals that sonication-induced aggregates have high ␤-content, and proteins with significant native ␣-helical structure show increased ␤-structure in the aggregates. Ultrastructural analysis by electron microscopy reveals a range of morphologies for the sonication-induced aggregates, including fibrils with diameters of 5-20 nm. The addition of preformed aggregates to unsonicated protein solutions results in accelerated and enhanced formation of additional aggregates upon heating. The dye-binding and structural characteristics, as well as the ability of the sonication-induced aggregates to seed the formation of new aggregates are all similar to the properties of amyloid. These results have important implications for the use of sonication in food, biotechnological and medical applications, and for research on protein aggregation and conformational disorders.

The effects of shear flow on protein structure and function

“…In one particular study, a range of structurally diverse protein systems including BSA, myoglobin, lysozyme, Tm0979, SOD and hisactophin were shown to generate amyloid like structures following sonication. 76 Shear effects on protein aggregation have also been studied in uniform flow fields. For example, a shear-induced nucleation, without flow enhanced aggregation, of preheated b-lactoglobulin solutions (0.5 wt%) at low pH has been reported.…”

Ultrasonication: An Efficient Agitation for Accelerating the Supersaturation-Limited Amyloid Fibrillation of Proteins

“…The first paper suggesting the usefulness of ultrasonication for amyloid nucleation was by Stathopulos et al 34) They showed that, for various proteins (i.e., bovine serum albumin, horse heart myoglobin, hen egg white lysozyme, Tm0979, recombinant hisactophilin, and human cytosolic Cu/Zn superoxide dismutase), ultrasonication results in the formation of amyloid-like aggregates. They suggested that protein unfolding and aggregation are caused by the ultrasonication at the water-air interface of cavitation bubbles, leading to the amyloid nucleation.…”

“…Stathopulos et al 34) showed that ultrasonication results in the formation of amyloid-like aggregates. Subsequently, amyloid fibrillation of various proteins such as -synuclein, 52) 2-m, 53) transthyretin, 54) and mouse prion proteins 50) was reported to be accelerated by ultrasonic irradiation.…”

A Sensitive Aβ Oligomerization Assay for Identification of Small Molecule Inhibitors

“…The majority of assays used for inhibitor identification apply dye-binding protocols that differentiate between free dye and dye bound to peptide aggregates by measuring spectral shifts. These dyes bind to peptide aggregates by non-specific, hydrophobic interactions and are unable to discern between low-versus highmolecular weight aggregates [53][54][55][56][57][58]. This has become of concern since recent studies suggest that the early stages of peptide oligomerization forming low-molecular weight aggregates may represent the most toxic form in vivo [7,9,10,59].…”