The folded protein as a viscoelastic solid
Department of Physics and Astronomy, University of California Los Angeles Los Angeles, CA 90095-1547, USA
Accepted: 16 August 2011
We apply a nanorheology technique to explore the mechanical properties of a globular protein in the frequency range 10 Hz–10 kHz and find that the folded state of the protein behaves like a viscoelastic solid. For increasing amplitude of the forcing, we observe three different regimes: linear elasticity, then a regime of viscoelastic but reversible deformations, and finally an irreversible regime. The second regime, which has the signature of a viscoelastic solid, gives access to the internal dissipation coefficient of the folded state, for which we find γ≈4×10− 5 kg/s, corresponding to an internal viscosity η∼104 Pa·s for frequencies below ∼10 Hz. We propose that the large discrepancy between this value, which agrees with previous AFM indentation experiments, and the value of the internal viscosity extracted from refolding experiments is a consequence of the viscoelastic nature of the protein's mechanics. Thus the present method yields detailed measurements of the mechanics of the folded state.
PACS: 87.15.-v – Biomolecules: structure and physical properties / 62.25.-g – Mechanical properties of nanoscale systems / 83.60.Bc – Linear viscoelasticity
© EPLA, 2011