Adsorption of the amyloid β40 monomer on charged gold nanoparticles and slabs: a molecular dynamics study

Negatively charged nanoparticles are known to inhibit the fibrillation of amyloidogenic protein amyloid beta (A beta 40), though the overall charge on the protein is negative. In this work a molecular dynamics study is reported to investigate the interaction of A beta 40 on negatively charged gold nanoparticles (3-5 nm) and charged (positive and negative) and neutral gold slabs. The equilibrium structures of A beta 40 on gold surfaces are characterized using residue-specific contacts on the gold surface, secondary structure analysis and binding free energy calculations. The simulation results reveal that the A beta 40 protein in water interconverts into beta-sheets, which are building blocks of the mature fibrils, whereas on gold nanoparticles A beta 40 unfolds and adsorbs. Both the negatively charged gold nanoparticles and gold slabs arrest the formation of beta-sheets in A beta 40, whereas the positively charged gold slab does not inhibit the formation of beta-sheets. The residue-specific interactions between A beta 40 and the gold surfaces are important in governing the adsorption of A beta 40 on charged surfaces.