Exceptional rigidity and biomechanics of amyloid revealed by 4D electron microscopy
Amyloid is an important class of proteinaceous material because of its close association with protein misfolding disorders such as Alzheimer's disease and type II diabetes. Although the degree of stiffness of amyloid is critical to the understanding of its pathological and biological functions, current estimates of the rigidity of these β-sheet–rich protein aggregates range from soft (10^8 Pa) to hard (10^(10) Pa) depending on the method used. Here, we use time-resolved 4D EM to directly and noninvasively measure the oscillatory dynamics of freestanding, self-supporting amyloid beams and their rigidity. The dynamics of a single structure, not an ensemble, were visualized in space and time by imaging in the microscope an amyloid–dye cocrystal that, upon excitation, converts light into mechanical work. From the oscillatory motion, together with tomographic reconstructions of three studied amyloid beams, we determined the Young modulus of these highly ordered, hydrogen-bonded β-sheet structures. We find that amyloid materials are very stiff (10^9 Pa). The potential biological relevance of the deposition of such a highly rigid biomaterial in vivo are discussed.
Additional Information© 2013 National Academy of Sciences. Contributed by Ahmed H. Zewail, May 23, 2013 (sent for review April 4, 2013). Published online before print June 19, 2013. This manuscript was reviewed by three experts: D. Eisenberg, C.M. Dobson and T.P.J. Knowles. A.W.P.F. was previously a postdoctoral associate with C.M. Dobson who is a pioneer in the field of amyloid research. We are grateful to all reviewers for their helpful and penetrating comments. We thank H. B. Gristick for help with sample preparation and for useful discussions. This work was supported by National Science Foundation Grant DMR-0964886 and Air Force Office of Scientific Research Grant FA9550-11-1-0055 to the Gordon and Betty Moore Center for Physical Biology at the California Institute of Technology. Author contributions: A.W.P.F., S.T.P., and A.H.Z. designed research, performed research, contributed new reagents/analytic tools, analyzed data, and wrote the paper. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1309690110/-/DCSupplemental.
Published - PNAS-2013-Fitzpatrick-10976-81.pdf
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Supplemental Material - pnas.201309690SI.pdf