Amyloids and Oligomers. Curvilinear and annular structures and their interaction with exosomes and whole cells

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Background:- There are a number of proteins that clump together to form ordered fibrillary assembles known as amyloids. Amyloids can have functional roles in yeast and bacteria. They also represent potential novel nanomaterials. Furthermore, misfolding and self-assembly of proteins, such as the prion protein, are link with diseases including, mad-cow disease (BSE) and scrapie in sheep. While amyloid beta protein (Ab) is linked to Alzheimer's in humans.In addition to long unbranched fibrils, specific pre-fibrillary assemblies are often formed. These include annular (donut-ring) shaped structures as well as more curvilinear protofibrils. These prefibrillar structures often have a high affinity for lipid bilayers, their interaction with the lipid membrane can disrupt cellular processes and balance; this causes a cascade of events culminating in cell death. Ab-aggregates are toxic to cells by disrupting cell integrity through the 'carpeting' of the cell membrane, or via the formation of small channels that span the cell-wall, thereby causing an uncontrolled flow of calcium ions into the cell. Understanding these processes is key to uncovering the mechanism by which Ab causes cell toxicity. At present, high resolution molecular imaging of these interactions, in native-like conditions, has been limited, while ion channel measurements have focused on reconstituted artificial lipid bilayers, which poorly approximate the behaviour of Ab channel formation in cellular membranes. Aims:- We want to investigate the fundamental process of Ab interactions with lipid membranes. Using powerful electron microscopes under cryogenic conditions we will image the annular (donut-ring) structures that form channels across lipid membranes. Using cryo-electron tomography, we will obtain three-dimensional molecular details of Ab carpeting the cell derived membrane surface under near native conditions. Furthermore, we aim to probe the mechanistic details of Ab42 ion-channel formation in cellular membranes using electrophysiology methods. We will determine the size and number of Ab channels that typically form on a neuron with different Ab preparations. In this way we will uncover the likely effects that Ab42 ion channels have on cellular processes under physiologically relevant conditions. We will explore Ab channel formation on both the extra- and intra-cellular membrane face of neurons. Significance:- The structures of prefibrillar assemblies will inform the wider amyloid field. We hope this study will give us a deeper understanding of how different Ab assemblies impact cell viability. These studies will inform the wider amyloid field. We expect our studies to highlight the key role of Ab in disrupting membrane integrity in the early stages of dementia. Our team of experts is well placed to investigate these fundamental interactions.