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Biophys J, February 2001, p. 597-605, Vol. 80, No. 2

Modeling AFM-Induced PEVK Extension and the Reversible Unfolding of Ig/FNIII Domains in Single and Multiple Titin Molecules

Bo Zhang and John Spencer Evans

Laboratory for Chemical Physics, Department of Chemistry, New York University, New York, New York 10010 USA

Molecular elasticity is associated with a select number of polypeptides and proteins, such as titin, Lustrin A, silk fibroin, and spider silk dragline protein. In the case of titin, the globular (Ig) and non-globular (PEVK) regions act as extensible springs under stretch; however, their unfolding behavior and force extension characteristics are different. Using our time-dependent macroscopic method for simulating AFM-induced titin Ig domain unfolding and refolding, we simulate the extension and relaxation of hypothetical titin chains containing Ig domains and a PEVK region. Two different models are explored: 1) a series-linked WLC expression that treats the PEVK region as a distinct entropic spring, and 2) a summation of N single WLC expressions that simulates the extension and release of a discrete number of parallel titin chains containing constant or variable amounts of PEVK. In addition to these simulations, we also modeled the extension of a hypothetical PEVK domain using a linear Hooke's spring model to account for "enthalpic" contributions to PEVK elasticity. We find that the modified WLC simulations feature chain length compensation, Ig domain unfolding/refolding, and force-extension behavior that more closely approximate AFM, laser tweezer, and immunolocalization experimental data. In addition, our simulations reveal the following: 1) PEVK extension overlaps with the onset of Ig domain unfolding, and 2) variations in PEVK content within a titin chain ensemble lead to elastic diversity within that ensemble.

Biophys J, February 2001, p. 597-605, Vol. 80, No. 2
© 2001 by the Biophysical Society   0006-3495/01/02/597/09  $2.00


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E. H. Lee, J. Hsin, O. Mayans, and K. Schulten
Secondary and Tertiary Structure Elasticity of Titin Z1Z2 and a Titin Chain Model
Biophys. J., September 1, 2007; 93(5): 1719 - 1735.
[Abstract] [Full Text] [PDF]


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Copyright © 2001 by the Biophysical Society.