Nanomechanical properties of SSTSAA microcrystals are dominated by the inter-sheet packing

Abstract

Amyloid fibrils have been associated with human disease for many decades, but it has also become apparent that they play a functional, non-disease-related role in e.g. bacteria and mammals. Moreover, they have been shown to possess interesting mechanical properties that can be harnessed for future man-made applications. Here, the mechanical behaviour of SSTSAA microcrystals has been investigated. The SSTSAA peptide organization in these microcrystals has been related to that in the corresponding amyloid fibrils. Using high-pressure X-ray diffraction experiments, the bulk modulus K, which is the reciprocal of the compressibility β , has been calculated to be 2.48 GPa. This indicates that the fibrils are tightly packed, although the packing of most native globular proteins is even better. It is shown that the value of the bulk modulus is mainly determined by the compression along the c -axis, that relates to the inter-sheet distance in the fibrils. These findings corroborate earlier data obtained by AFM and molecular dynamics simulations that showed that mechanical resistance varies according to the direction of the applied strain, which can be related to packing and hydrogen bond contributions. Pressure experiments provide complementary information to these techniques and help to acquire a full mechanical characterization of biomolecular assemblies. This article is part of the theme issue ‘Exploring the length scales, timescales and chemistry of challenging materials (Part 2)’.

Exploring the length scales, timescales and chemistry of challenging materials (Part 2)

“…The papers collected in these two themed issues emphasize how understanding the length and timescales that control material process and properties cross disciplinary boundaries as illustrated effectively in the contribution by Filip Meersman and colleagues [ 16 ], who use high pressure techniques and X-ray diffraction to evaluate the mechanical properties of biomolecular assemblages. Amyloid fibrils have been studied extensively, primarily because of their association with neurodegenerative diseases [ 17 ], although it is now recognized that their occurrence is more widespread, and they are viewed as playing an essential part of polypeptide chain behaviour.…”

“…Amyloid fibrils have been studied extensively, primarily because of their association with neurodegenerative diseases [ 17 ], although it is now recognized that their occurrence is more widespread, and they are viewed as playing an essential part of polypeptide chain behaviour. The potential use of amyloid fibrils in bioengineering applications means that their mechanical strength is of particular interest and Meersman et al [ 16 ] present diffraction patterns for microcrystalline samples encapsulated in a diamond anvil cell to pressures of 12.8 GPa; the structures become disordered above 8 GPa so Meersman et al have used these data up to 1.4 GPa to obtain their bulk modulus. The microcrystals are tightly packed, and compression of these fibrils is anisotropic; the longer, crystallographic a -axis is the least compressible while the c -axis, corresponding to the inter-sheet distance, is more compressible suggesting that the mechanical behaviour of these biomaterials is related to both packing and hydrogen bonding.…”