UC San Diego

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder affecting millions of people worldwide and the number is projected to rapidly increase in the coming years. AD severely impairs an individual’s memory, cognitive abilities leading to dementia and neuronal death. Although a large body of research work has gone into understanding AD in the past couple of decades, there is still no clear consensus on the molecular nature of the disease progression and thus, no cure or robust treatment methodologies have been found. The molecular hallmark of AD is the presence of extracellular, lesion-like deposits of a protein called Amyloid-β (Aβ). The amyloid hypothesis argues that the presence of these extracellular deposits of Aβ triggers a neuropathological cascade of events which lead to the death of the neuron. The amyloid ion channel hypothesis suggests that Aβ is capable of forming high conductance, cation selective channels leading to calcium dyshomeostasis in neurons, leading to neuronal death. This dissertation investigates the biophysical, structural, and functional properties of full length Aβ and its various truncated and post translationally modified forms. We show that Aβ isoforms are also capable of causing ion flux in lipid bilayers, thus adding additional support to the amyloid channel-based neurotoxicity. As the exact structure and morphology of Aβ oligomers involved in the cytotoxicity are poorly characterized until now, we introduce single molecule force spectroscopy techniques that shed new light on the morphological characteristics of Aβ oligomeric species. The technique also helps uncover mechano-biological coupling involved in the process of protein-membrane structural organization. Finally, we describe the development and implementation of a combined atomic force microscopy and total internal reflection fluorescence (AFM-TIRF) microscopy system for high spatiotemporal and multiparametric studies of membrane-protein interactions. AD is a multifactorial disease and studies involving the convergence of bio -physical, -chemical, and -mechanical aspects of membrane-protein interactions and their structure-function relationships provides additional insights into the molecular nature of Aβ, and the probable mechanisms involved in the AD cascade. The understanding of molecular landscape of Aβ interactions is critical to the development of therapeutic interventions to arrest the progression of AD and reverse cognitive decline.