Tension-dependent structural deformation alters single-molecule transition kinetics.
We analyze the response of a single nucleosome to tension, which serves as a prototypical biophysical measurement where tension-dependent deformation alters transition kinetics. We develop a statistical-mechanics model of a nucleosome as a wormlike chain bound to a spool, incorporating fluctuations in the number of bases bound, the spool orientation, and the conformations of the unbound polymer segments. With the resulting free-energy surface, we perform dynamic simulations that permit a direct comparison with experiments. This simple approach demonstrates that the experimentally observed structural states at nonzero tension are a consequence of the tension and that these tension-induced states cease to exist at zero tension. The transitions between states exhibit substantial deformation of the unbound polymer segments. The associated deformation energy increases with tension; thus, the application of tension alters the kinetics due to tension-induced deformation of the transition states. This mechanism would arise in any system where the tether molecule is deformed in the transition state under the influence of tension.
Department of Chemical Engineering, Stanford University, Stanford, CA 94305, USA.
B
B
Sudhanshu
S
S
Mihardja
E F
EF
Koslover
S
S
Mehraeen
C
C
Bustamante
A J
AJ
Spakowitz
D001703:Biophysics; D007700:Kinetics; D008962:Models, Theoretical; D015394:Molecular Structure; D009707:Nucleosomes / Q000737:chemistry*
D009707:Nucleosomes
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