Modification of amyloid fiber formation of alpha-synuclein and amyloid-beta by small molecules

Abstract

Alzheimer's and Parkinson's disease are the two most common neurodegenerative diseases. Understanding how their associated proteins, Amyloid-beta (Abeta) and alpha-Synuclein (alphaSyn), respectively, are linked to the related pathologies is a critical area of current research. In these and other neurodegenerative diseases, proteinaceous deposits have been found in the brain. It has been shown that these deposits have a common amyloid fibril structure, composed of anti-parallel beta-sheets perpendicular to the fiber axis. However, the role of these amyloid fibers in causing the neurodegeneration is unclear. Recent evidence suggests a pre-fibrillar structure, common to many neurodegenerative disease-related proteins, may in fact be the primary toxic species, and the amyloid fibers are either a nontoxic dead-end species, or a beneficial mechanism to clear damaged proteins.;In this work, I studied the structural properties of alphaSyn intermediates populated along the fibril formation pathway using various biophysical and biochemical methods, including transmission electron microscopy, atomic force microscopy, native gel electrophoresis, optical absorption spectroscopy and fluorescence spectroscopy. I show that the aggregation of alphaSyn into amyloid fibrils follows a hierarchical mechanism, with accumulation of a cylindrical oligomeric intermediate, which is consistent with the "amyloid pore" model of amyloid toxicity.;To investigate how the aggregation process may be modified by small molecules, in an effort to aid in the development of therapeutic interventions for neurodegenerative diseases, I have studied the fibril formation behaviors of alphaSyn and Abeta in the presence of heme or target molecules from a library of aromatic organic compounds. I found that during the aggregation, heme is able to bind the alphaSyn in a specific fashion, and the interaction promotes the conversion of alphaSyn to smaller, potentially less harmful cylindrical intermediates, thereby inhibiting the fibrillation process. On the other hand, the interactions of alphaSyn or Abeta with the molecules in the small molecule library show disparate effects: some molecules promote fibril formation, some promote cylindrical intermediates, while the others show no effect. Together, these results serve as a foundation for future design of small molecule inhibitors and diagnostic agents of amyloid fiber formation. The results also provide insight into the mechanism of protein aggregation applicable to the understanding of many neurodegenerative diseases.