Characterization of amyloid β fibril formation under microgravity conditions

Abstract

Amyloid fibrils are self-assembled and ordered proteinaceous supramolecules structurally characterized by the cross-β spine. Amyloid formation is known to be related to various diseases typified by neurogenerative disorders and involved in a variety of functional roles. Whereas common mechanisms for amyloid formation have been postulated across diverse systems, the mesoscopic morphology of the fibrils is significantly affected by the type of solution condition in which it grows. Amyloid formation is also thought to share a phenomenological similarity with protein crystallization. While many studies have demonstrated the effect of gravity on protein crystallization, its effect on amyloid formation has not been reported. In this study, we conducted an experiment at the International Space Station (ISS) to characterize fibril formation of 40residue amyloid β (Aβ(1-40)) under microgravity conditions. Our comparative analyses revealed that the Aβ(1-40) fibrilization progresses much more slowly on the ISS than on the ground, similarly to protein crystallization. Furthermore, microgravity promoted the formation of distinct morphologies of Aβ(1-40) fibrils. Our findings demonstrate that the ISS provides an ideal experimental environment for detailed investigations of amyloid formation mechanisms by eliminating the conventionally uncontrollable factors derived from gravity. IntroductionCertain proteins are known to self-assemble into ordered supramolecular structures, such as filaments and even crystals, under specific physiological and pathological conditions 1,2 . The cytoskeletons present in all cells are made of such filamentous proteins, which dynamically assemble and disassemble to control cell morphology, movement, and signaling in physiological processes 1,3 . In contrast, filamentous protein aggregates known as amyloid fibrils are actively involved in pathological processes and are associated with various diseases, including neurogenerative disorders and diabetes 4-6 . Each of these diseases is characterized by a specific amyloidogenic protein, but it has been suggested that a common molecular mechanism governs fibril formation across these diverse systems. Amyloids may also play a variety of functional roles in many organisms and have been regarded as potentially useful nanomaterials in recent years 7-9 . Therefore, a detailed characterization of the self-assembling mechanism of amyloid fibrils and the resulting morphology is essential for developing therapeutic strategies for amyloidopathy and gaining the knowledge needed to create future nanomaterials.Increasing evidence provided by cryo-electron microscopy (cryo-EM) 10-12 and solid-state NMR spectroscopy [13][14][15] demonstrate that the morphology of amyloid fibrils is significantly affected by various solution conditions, such as protein concentration, ionic strength, pH, temperature, and pressure 9 . X-ray diffraction studies show that amyloid fibrils share similar structural features characterized by a cross-β spine: a double β-sheet with each sheet runni...