A kinetic molecular model of the reversible unfolding and refolding of titin under force extension

Bo Zhang, Guangzhao Xu, John Evans

Research output: Contribution to journalArticle

Abstract

Molecular elasticity is a physicomechanical property that is associated with a select number of polypeptides and proteins, such as the giant muscle protein, titin, and the extracellular matrix protein, tenascin. Both proteins have been the subject of atomic force microscopy (AFM), laser tweezer, and other in vitro methods for examining the effects of force extension on the globular (FNIII/Ig-like) domains that comprise each protein. In this report we present a time-dependent method for simulating AFM force extension and its effect on FNIII/Ig domain unfolding and refolding. This method treats the unfolding and refolding process as a standard three-state protein folding model (U ⇆ T ⇆ F, where U is the unfolded state, T is the transition or intermediate state, and F is the fully folded state), and integrates this approach within the wormlike chain (WLC) concept. We simulated the effect of AFM tip extension on a hypothetical titin molecule comprised of 30 globular domains (Ig or FNIII) and 25% Pro-Glu-Val-Lys (PEVK) content, and analyzed the unfolding and refolding processes as a function of AFM tip extension, extension rate, and variation in PEVK content. In general, we find that the use of a three-state protein-folding kinetic-based model and the implicit inclusion of PEVK domains can accurately reproduce the experimental force- extension curves observed for both titin and tenascin proteins. Furthermore, our simulation data indicate that PEVK domains exhibit extensibility behavior, assist in the unfolding and refolding of FNIII/Ig domains in the titin molecule, and act as a force 'buffer' for the FNIII/Ig domains, particularly at low and moderate extension forces.

Original languageEnglish (US)
Pages (from-to)1306-1315
Number of pages10
JournalBiophysical Journal
Volume77
Issue number3
StatePublished - Sep 1999

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Connectin
Molecular Models
Atomic Force Microscopy
Tenascin
Protein Folding
Proteins
Optical Tweezers
Muscle Proteins
Extracellular Matrix Proteins
Elasticity
Buffers
Immunoglobulin Domains
Peptides

ASJC Scopus subject areas

  • Biophysics

Cite this

A kinetic molecular model of the reversible unfolding and refolding of titin under force extension. / Zhang, Bo; Xu, Guangzhao; Evans, John.

In: Biophysical Journal, Vol. 77, No. 3, 09.1999, p. 1306-1315.

Research output: Contribution to journalArticle

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