Structure of Unmodified and Pyroglutamylated Amyloid Beta Peptide in Lipid Membranes

Alzheimer\u27s Disease (AD) is a devastating neurodegenerative disease that is characterized by brain atrophy, neuronal and synaptic loss, cognitive decline, trouble handling activities of daily life, and ultimately leads to death. Worldwide, at least 30 million people suffer from AD, with 5.8 million suffering in the US alone. Despite extensive basic and clinical research, the underlying molecular mechanisms behind AD remain largely unknown. There are four FDA-approved compounds are used for alleviating symptoms but have no curative potency. The first potentially disease-modifying AD drug, aducanumb, was approved by FDA in June 2021. The main histopathological traits of AD are the Amyloid-beta (Aβ) peptide and the tau protein. Aβ aggregates to form extracellular plaques in brain parenchyma and vasculature while tau forms intraneuronal tangles. Aβ is produced by enzymatic cleavage of the amyloid precursor protein (APP) in the brain. Once APP cleavage occurs, Ab monomers either aggregate extracellularly to form buildups of sticky plaque or embed themselves within the neuronal cell membrane to form pores, causing homeostatic dysregulation and eventually cell death. The mechanism of membrane pores formed by Ab and the pore structure remain to be characterized. This study aims to analyze the structure of four Aβ species in lipid membranes. These are the most abundant form of Aβ, Aβ1-40, and the more cytotoxic form, Aβ1-42, as well as their pyroglutamylated counterparts, pEAβ3-40 and pEAβ3-42, which are hypertoxic. These peptides have been studied using biophysical approaches, i.e., circular dichroism, fluorescence spectroscopy, and Fourier transform infrared spectroscopy. Elucidation of the structure of Aβ membrane pores provides valuable insight into the mechanism of Aβ toxicity and may help develop novel therapies for the lethal mystery that is AD