Amyloid transition of ubiquitin on silver nanoparticles produced by pulsed laser ablation in liquid as a function of stabilizer and single-point mutations

The interaction of nanoparticles with proteins has emerged as a key issue in addressing the problem of nanotoxicity. We investigated the interaction of silver nanoparticles (AgNPs), produced by laser ablation with human ubiquitin (Ub), a protein essential for degradative processes in cells. The surface plasmon resonance peak of AgNPs indicates that Ub is rapidly adsorbed on the AgNP surface yielding a protein corona; the Ub-coated AgNPs then evolve into clusters held together by an amyloid form of the protein, as revealed by binding of thioflavin T fluorescent dye. Transthyretin, an inhibitor of amyloid-type aggregation, impedes aggregate formation and disrupts preformed AgNP clusters. In the presence of sodium citrate, a common stabilizer that confers an overall negative charge to the NPs, Ub is still adsorbed on the AgNP surface, but no clustering is observed. Ub mutants bearing a single mutation at one edge ? strand (i.e. Glu16Val) or in loop (Glu18Val) behave in a radically different manner. Human ubiquitin forms amyloids on the surface of silver nanoparticles produced by laser ablation, which induce clustering of the nanoparticles and thioflavin T fluorescence. In the presence of sodium citrate as a stabilizer, ubiquitin only forms a protein corona. A single mutation (Glu16Val) at one edge ? strand of the protein can deeply influence the amyloid transition (see figure). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.