Self-Assembly of Protein Fibrils in Microgravity

Abstract

Deposits of insoluble protein fibrils in human tissue are associated with amyloidosis and neurodegenerative diseases. Different proteins are involved in each disease; all are soluble in their native conformation in vivo, but by molecular self-assembly, they all form insoluble protein fibril deposits with a similar cross β-sheet structure. This paper reports the results of an experiment in molecular self-assembly carried out in microgravity on the International Space Station (ISS). The Self-Assembly in Biology and the Origin of Life (SABOL) experiment was designed to study the growth of lysozyme fibrils in microgravity. Lysozyme is a model protein that has been shown to replicate the aggregation processes of other amyloid proteins. Here the design and performance of the experimental hardware is described in detail. The flight experiment was carried to the ISS in the Dragon capsule of the SpaceX CRS-5 mission and returned to Earth after 32 days. The lysozyme fibrils formed in microgravity aboard the ISS show a distinctly different morphology compared to fibrils formed in the ground-control (G-C) experiment. The fibrils formed in microgravity are shorter, straighter, and thicker than those formed in the laboratory G-C experiment. For two incubation periods, (2) about 8.5 days and (3) about 14.5 days, the average ISS and G-C fibril diameters are respectively: \matrix{{Period\,2} \hfill & {} \hfill & {{D_{ISS}} = 7.5{\rm{nm}} \pm 31\% ,} \hfill \cr {} \hfill & {\rm and} \hfill & {{D_{G - C}} = 3.4{\rm{nm}} \pm 31\%} \hfill \cr {Period\,3} \hfill & {} \hfill & {{D_{ISS}} = 6.2{\rm{nm}} \pm 33\% ,} \hfill \cr {} \hfill & {\rm and} \hfill & {{D_{G - C}} = 3.6{\rm{nm}} \pm 33\% .}}

Influence of Centrifugation and Shaking on the Self-Assembly of Lysozyme Fibrils

“…At the same time, the literature on microgravity effects is scarce. Morphological [ 36 ] and kinetical alterations [ 37 ] were reported for samples fibrillating in microgravity. Interestingly, flows and gravitational forces are directional, and it was reported that the geometry of the applied forces plays a role in the destabilization of the protein [ 38 ].…”

Changes in interstitial fluid flow, mass transport and the bone cell response in microgravity and normogravity

“…It was speculated that the changes seen were due to lower transport rates for larger aggregates in this convection-limited environment. Furthermore, Bell et al 108 investigated molecular self-assembly on the ISS and reported that lysozyme protein fibrils showed a distinctly different morphology. The fibrils formed in microgravity were shorter, straighter, and thicker than those formed in ground-based studies.…”

Enhanced assembly of bacteriophage T7 produced in cell-free reactions under simulated microgravity

“…Many biological processes as well as biomolecular self-assembly depend on gravity. For example, in microgravity, proteins form larger crystals with fewer defects 14 , and amyloid fibrils nucleate and grow differently in simulated microgravity 15,16 . Comparing virus assembly in orbiter flight studies against ground controls, polyomavirus assembled into larger and more homogeneous capsomeres but did not form capsid-like structures 17 .…”