(544c) Effects of Osmolytes On Amyloid Protein Surface and Membrane Activity

The misfolding and aggregation of largely intrinsically disordered amyloid proteins into beta-sheet rich fibrillar deposits are implicated in the pathogenesis of over 20 neurodegenerative diseases, including Alzheimer’s and Parkinson’s diseases. There are currently no cures for these disorders due to, at least in part, a lack of understanding of the mechanisms by which amyloid proteins aggregate. We have shown that interfaces, such as the air/water and lipid membrane interfaces, can catalyze the formation of partially folded or structurally compacted aggregation competent intermediates that subsequently irreversibly assemble into higher order fibrillar aggregates. In this study, we examine the effects of osmolytes, sucrose and urea, on the surface and membrane activities of the amyloid-beta protein in an effort to better understand the effects of the cellular environment on interface-induced amyloid protein aggregation. To evaluate the surface activity of amyloid-beta, adsorption isotherms (surface pressures vs. time) of amyloid-beta to the air/subphase interface was measured in a Langmuir trough on subphases containing varying concentrations of sucrose (0 – 1 M) and urea (0 – 6 M). Membrane activity was measured by carrying out constant pressure insertion assays into anionic DMPG and zwitterionic DPPC lipid monolayers in a Langmuir trough. The preferentially excluded sucrose is found to significantly decrease the lag time and increase the rate of amyloid-beta absorption to the air/water interface.  Additionally, finally surface pressure reached by the adsorption of the amyloid-beta protein also increased with increasing sucrose concentration in the subphase. Our results thus indicate that sucrose increases surface and membrane activities of amyloid-beta.  Urea, a chaotrope that preferentially bind to protein backbone and increases protein solubility in solution, surprisingly, also increased amyloid-beta surface activity. Our data thus far indicate that the crowded cellular environment can significantly enhance driving forces for interface-induced amyloid-protein aggregation. Investigations are currently underway to evaluate the effect of urea on amyloid-beta membrane activity and the effects of osmolytes on interface-induced amyloid-beta aggregation.