Internal water dynamics in hydration shells of amyloid-beta species - One of the hallmarks of Alzheimer’s disease is the presence of neurotoxic amyloid-β (Aβ) deposits in brain tissue. All Aβ species from oligomers to fibrils exist in a dynamic equilibrium, which is believed to trigger a pathological cascade implicating multiple aggregation-prone proteins. Mechanisms of in vivo Aβ formation, stabilization, and aggregation kinetics are complex. Further, chemical modifications of the primary sequence, including post-translational modifications play a role in regulating aggregation, cyto-toxicity, as well as causing an early or sporadic onset of the disease. One of the understudied fundamental factors is interactions with water and hydration shells, which are nonetheless important in defining the structure and dynamics of oligomers and fibrils. We hypothesize that water structure and dynamics in the hydration shell of the oligomers and fibrils is an important factor in stabilization and aggregation of these species. After all, water must be displaced to form hydrophobic regions needed for oligomers and protofibrils formation. Water also must be displayed when these species interact with cell membranes. Our focus will be placed on characterization of water dynamics in oligomers and fibrils spanned by Aβ1-40 with the native sequence, two toxic post-translational modifications, and two fibrillar mutants. We will utilize established and new solid-state NMR methodologies to probe the internal dynamics of hydration water in these systems. Hydration water dynamics will be then correlated with the membrane binding and membrane disruption properties of the Aβ variants, as well as with the flexibility of the fibrils themselves. The latter was determined in our prior studies funded by the NIH-R15 awards. The proposed work will be structured to maximize the preparation of undergraduates to enter the biomedical profession. Our main aim is characterization of water flexibility in hydration layers of oligomers and fibrils formed by native Aβ1-40, as well as its pyroglutamate-E3 and phosphorylated-S8 post-translationally modified variants, which have high aggregation propensities and cyto-toxicities. Additional modified fibrils comprised of the E22∆ Osaka familial mutation and protofibrils of the D23N Iowa variant will be probed. The main methodology will be deuterium and oxygen-17 solid-state NMR complemented with phenomenological modeling. The second aim will focus on a) correlations between hydration water dynamics and the dynamics of the Aβ species themselves, obtained in prior work with undergraduate researchers and b) correlations of water flexibility in the native and modified Aβ aggregates with their membrane-binding abilities and details of Aβ packing inside the membranes. Specifically, we will probe the ability of these species to bind to anionic membranes and adopt a β-sheet rich structure nucleated on the membrane surface, using liquid surface X-ray reflectivity and grazing incidence X-ray diffraction from a lipid monolayer in a Langmuir trough. This sub-aim will be in collaboration with the undergraduate-based laboratory of Dr. Vander Zanden at University of Colorado at Colorado Springs, bringing together two undergraduate-based labs.
