TY - JOUR
T1 - Twist-bend coupling and the statistical mechanics of the twistable wormlike-chain model of DNA
T2 - Perturbation theory and beyond
AU - Nomidis, Stefanos K.
AU - Skoruppa, Enrico
AU - Carlon, Enrico
AU - Marko, John F.
N1 - Funding Information:
Discussions with M. Laleman and T. Sakaue are gratefully acknowledged. S.N. acknowledges financial support from the Research Funds Flanders (FWO Vlaanderen) Grant No. VITO-FWO 11.59.71.7N and E.S. from KU Leu- ven Grant No. IDO/12/08. J.F.M. is grateful to the Francqui Foundation (Belgium) for financial support, and to the US NIH through Grants No. R01-GM105847, No. U54-CA193419, and No. U54-DK107980.
Publisher Copyright:
© 2019 American Physical Society.
PY - 2019/3/18
Y1 - 2019/3/18
N2 - The simplest model of DNA mechanics describes the double helix as a continuous rod with twist and bend elasticity. Recent work has discussed the relevance of a little-studied coupling G between twisting and bending, known to arise from the groove asymmetry of the DNA double helix. Here the effect of G on the statistical mechanics of long DNA molecules subject to applied forces and torques is investigated. We present a perturbative calculation of the effective torsional stiffness Ceff for small twist-bend coupling. We find that the "bare" G is "screened" by thermal fluctuations, in the sense that the low-force, long-molecule effective free energy is that of a model with G=0 but with long-wavelength bending and twisting rigidities that are shifted by G-dependent amounts. Using results for torsional and bending rigidities for freely fluctuating DNA, we show how our perturbative results can be extended to a nonperturbative regime. These results are in excellent agreement with numerical calculations for Monte Carlo "triad" and molecular dynamics "oxDNA" models, characterized by different degrees of coarse graining, validating the perturbative and nonperturbative analyses. While our theory is in generally good quantitative agreement with experiment, the predicted torsional stiffness does systematically deviate from experimental data, suggesting that there are as-yet-uncharacterized aspects of DNA twisting-stretching mechanics relevant to low-force, long-molecule mechanical response, which are not captured by widely used coarse-grained models.
AB - The simplest model of DNA mechanics describes the double helix as a continuous rod with twist and bend elasticity. Recent work has discussed the relevance of a little-studied coupling G between twisting and bending, known to arise from the groove asymmetry of the DNA double helix. Here the effect of G on the statistical mechanics of long DNA molecules subject to applied forces and torques is investigated. We present a perturbative calculation of the effective torsional stiffness Ceff for small twist-bend coupling. We find that the "bare" G is "screened" by thermal fluctuations, in the sense that the low-force, long-molecule effective free energy is that of a model with G=0 but with long-wavelength bending and twisting rigidities that are shifted by G-dependent amounts. Using results for torsional and bending rigidities for freely fluctuating DNA, we show how our perturbative results can be extended to a nonperturbative regime. These results are in excellent agreement with numerical calculations for Monte Carlo "triad" and molecular dynamics "oxDNA" models, characterized by different degrees of coarse graining, validating the perturbative and nonperturbative analyses. While our theory is in generally good quantitative agreement with experiment, the predicted torsional stiffness does systematically deviate from experimental data, suggesting that there are as-yet-uncharacterized aspects of DNA twisting-stretching mechanics relevant to low-force, long-molecule mechanical response, which are not captured by widely used coarse-grained models.
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U2 - 10.1103/PhysRevE.99.032414
DO - 10.1103/PhysRevE.99.032414
M3 - Article
C2 - 30999490
AN - SCOPUS:85063265597
VL - 99
JO - Physical Review E
JF - Physical Review E
SN - 2470-0045
IS - 3
M1 - 032414
ER -