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α-Helix Unwinding as Force Buffer in Spectrins.

Titleα-Helix Unwinding as Force Buffer in Spectrins.
Publication TypeJournal Article
Year of Publication2018
AuthorsTakahashi H, Rico F, Chipot C, Scheuring S
JournalACS Nano
Volume12
Issue3
Pagination2719-2727
Date Published2018 Mar 27
ISSN1936-086X
Abstract

Spectrins are cytoskeletal proteins located at the inner face of the plasma membrane, making connections between membrane anchors and the actin cortex, and between actin filaments. Spectrins share a common structure forming a bundle of 3 α-helices and play a major role during cell deformation. Here, we used high-speed force spectroscopy and steered molecular dynamics simulations to understand the mechanical stability of spectrin, revealing a molecular force buffering function. We find that spectrin acts as a soft spring at short extensions (70-100 Å). Under continuous external stretching, its α-helices unwind, leading to a viscous mechanical response over larger extensions (100-300 Å), represented by a constant-force plateau in force/extension curves. This viscous force buffering emerges from a quasi-equilibrium competition between disruption and re-formation of α-helical hydrogen bonds. Our results suggest that, in contrast to β-sheet proteins, which unfold in a catastrophic event, α-helical spectrins dominantly unwind, providing a viscous force buffer over extensions about 5 times their folded length.

DOI10.1021/acsnano.7b08973
Alternate JournalACS Nano
PubMed ID29390177