{
  "id": "1809.07050",
  "version": "v1",
  "published": "2018-09-19T08:14:30.000Z",
  "updated": "2018-09-19T08:14:30.000Z",
  "title": "Twist-bend coupling and the statistical mechanics of DNA: perturbation theory and beyond",
  "authors": [
    "Stefanos K. Nomidis",
    "Enrico Skoruppa",
    "Enrico Carlon",
    "John F. Marko"
  ],
  "comment": "16 pages, 6 figures",
  "categories": [
    "cond-mat.stat-mech",
    "cond-mat.soft",
    "q-bio.BM"
  ],
  "abstract": "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 $C_\\text{eff}$ 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 non-perturbative 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 non-perturbative 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.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2018-09-19T08:14:30.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "statistical mechanics",
      "twist-bend coupling",
      "perturbation theory",
      "long dna molecules subject",
      "dna twisting-stretching mechanics relevant"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 16,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}