Caraglio Michele, Micheletti Cristian, Orlandini Enzo
Dipartimento di Fisica e Astronomia Università di Padova and sezione CNISM, Via Marzolo 8, I-35131 Padova, Italy.
SISSA, International School for Advanced Studies, via Bonomea 265, I-34136 Trieste, Italy.
Phys Rev Lett. 2015 Oct 30;115(18):188301. doi: 10.1103/PhysRevLett.115.188301. Epub 2015 Oct 27.
Recent theoretical and experimental advances have clarified the major effects of knotting on the properties of stretched chains. Yet, how knotted chains respond to weak mechanical stretching and how this behavior differs from the unknotted case are still open questions and we address them here by profiling the complete stretching response of chains of hundreds of monomers and different topology. We find that the ratio of the knotted and unknotted chain extensions varies nonmonotonically with the applied force. This surprising feature is shown to be a signature of the crossover between the well-known high-force stretching regime and the previously uncharacterized low-force one. The observed differences of knotted and unknotted chain response increases with knot complexity and are sufficiently marked that they could be harnessed in single-molecule contexts to infer the presence and complexity of physical knots in micron-long biomolecules.
近期的理论和实验进展已阐明了打结对拉伸链性质的主要影响。然而，打结链如何响应微弱的机械拉伸以及这种行为与未打结情况有何不同仍是悬而未决的问题，我们在此通过剖析数百个单体且具有不同拓扑结构的链的完整拉伸响应来解决这些问题。我们发现，打结链与未打结链的伸长比随施加力呈非单调变化。这一惊人特征表明是著名的高力拉伸 regime 与此前未表征的低力拉伸 regime 之间转变的标志。观察到的打结链与未打结链响应的差异随结的复杂性增加而增大，且十分显著，以至于在单分子环境中可利用这些差异来推断微米长生物分子中物理结的存在及其复杂性。
