The opposite effect of ethylammonium nitrate and tetramethylguanidinium acetate ionic liquids on the amyloidogenesis of lysozyme

Amyloidogenesis is the process by which proteins form aggregated structures known as amyloid fibrils. They play a key role in a variety of biological processes in healthy organisms, are a characteristic signature of several pathological conditions, and have been exploited as advanced materials. As a result, being able to control amyloidogenesis can have important implications in health and material sciences. In this context, the family of organic electrolytes known as ionic liquids (ILs) can play a decisive role. Here we present a comprehensive investigation using atomic force microscopy (AFM), optical tweezers and neutron scattering into the effect of two model ILs, ethyl ammonium nitrate (EAN) and tetramethyl guanidinium acetate (TMGA), on the amyloidogenesis of lysozyme. The AFM study shows the presence of two distinct amyloid fibril morphologies for EAN and TMGA suggesting the presence of two different amyloidogenic pathways, both driven by single protein-IL interactions. Optical tweezers and neutron scattering investigations support and enrich this picture. It emerges that (i) EAN, by reducing the protein mechanical stability via a direct interaction with the protein monomer, favours the formation of oligomers that aggregate into thicker amyloid fibrils, whereas (ii) TMGA, by altering the protein hydration shell, favours the formation of proto-fibrils that aggregate into thinner amyloid fibrils. The AFM investigation also shows that, in the presence of both ILs in the solution, the EAN mechanism of interaction prevails over that of TMGA. This work demonstrates that the huge variety of available ILs can offer a new and vast playground to tune protein amyloidogenesis opening novel ways to use ILs in nano-bio applications from health to material sciences.