Compaction and tensile forces determine the accuracy of folding landscape parameters from single molecule pulling experiments |
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Authors: | Morrison Greg Hyeon Changbong Hinczewski Michael Thirumalai D |
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Institution: | School of Engineering and Applied Science, Harvard University, Cambridge, Massachusetts 02138, USA. |
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Abstract: | We establish a framework for assessing whether the transition state location of a biopolymer, which can be inferred from single molecule pulling experiments, corresponds to the ensemble of structures that have equal probability of reaching either the folded or unfolded states (P(fold)=0.5). Using results for the forced unfolding of a RNA hairpin, an exactly soluble model, and an analytic theory, we show that P(fold) is solely determined by s, an experimentally measurable molecular tensegrity parameter, which is a ratio of the tensile force and a compaction force that stabilizes the folded state. Applications to folding landscapes of DNA hairpins and a leucine zipper with two barriers provide a structural interpretation of single molecule experimental data. Our theory can be used to assess whether molecular extension is a good reaction coordinate using measured free energy profiles. |
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