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Publication# The static and dynamic structural heterogeneities of B-DNA: extending Calladine-Dickerson rules

Résumé

We present a multi-laboratory effort to describe the structural and dynamical properties of duplex B-DNA under physiological conditions. By processing a large amount of atomistic molecular dynamics simulations, we determine the sequence-dependent structural properties of DNA as expressed in the equilibrium distribution of its stochastic dynamics. Our analysis includes a study of first and second moments of the equilibrium distribution, which can be accurately captured by a harmonic model, but with nonlocal sequence-dependence. We characterize the sequence-dependent choreography of backbone and base movements modulating the non-Gaussian or anharmonic effects manifested in the higher moments of the dynamics of the duplex when sampling the equilibrium distribution. Contrary to prior assumptions, such anharmonic deformations are not rare in DNA and can play a significant role in determining DNA conformation within complexes. Polymorphisms in helical geometries are particularly prevalent for certain tetranucleotide sequence contexts and are always coupled to a complex network of coordinated changes in the backbone. The analysis of our simulations, which contain instances of all tetranucleotide sequences, allow us to extend Calladine-Dickerson rules used for decades to interpret the average geometry of DNA, leading to a set of rules with quantitative predictive power that encompass nonlocal sequence-dependence and anharmonic fluctuations.

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Concepts associés (8)

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Naturally occurring intrastrand oxidative crosslink lesions have proven to be a potent source of endogenous DNA damage. Among the variety of lesions that can be formed and have been identified, G[8-5]C damage (in which the C8 atom of a guanine is covalently bonded to the CS atom of a nearby cytosine belonging to the same strand) occurs with a low incidence yet takes on special importance because of its high mutagenicity. Hybrid Car-Parrinello molecular dynamics simulations, rooted in density functional theory and coupled to molecular mechanics, have been performed to shed light on the cyclization process. The activation free energy of the reacting subsystem embedded in a solvated dodecamer is estimated to be similar to 12.4 kcal/mol, which is similar to 3 kcal/mol higher than the value for the prototypical G[8-5m]T lesion inferred employing the same theoretical framework [Garrec, 3., Patel, C., Rothlisberger, U., and Dumont, E. (2012) J. Am. Chem. Soc. 134, 2111-2119]. This study also situates the G[8-5m]mC lesion at an intermediate activation free energy (similar to 10.5 kcal/mol). The order of reactivity in DNA (T-center dot > mC(center dot) > C-center dot) is reversed compared to that in the reacting subsystems in the gas phase (C-center dot > mC(center dot) > T-center dot), stressing the crucial role of the solvated B-helix environment. The results of our simulations also characterize a more severe distortion for G[8-5]C than for methylene-bridged intrastrand cross-links.

Sequence dependent mechanics of DNA is believed to play a central role in the functioning of the cell through the expression of genetic information. Nucleosome positioning, gene regulation, DNA looping and packaging within the cell are only some of the processes that are believed to be at least partially governed by mechanical laws. Therefore it is important to understand how the sequence of DNA affects its mechanical properties. For exploring the mechanical properties of DNA, various discrete and continuum models have been, and continue to be, developed. A large family of these models, including the model considered in this work, assume that bases or base pairs of DNA are rigid bodies. The most standard are rigid base pair models, with parameters either obtained directly from experimental data or from Molecular Dynamics (MD) simulations. The drawback of current experimental data, such as crystal structures, is that only small ensembles of configurations are available for a small number of sequences. In contrast, MD simulations allow a much more detailed view of a larger number of DNA sequences. However, the drawback is that the results of these simulations depend on the choice of the simulation protocol and force field parameters. MD simulations also have sequence length limitations and are currently too intensive for (linear) molecules longer than a few tens of base pairs. The only way to simulate longer sequences is to construct a coarse-grain model. The goal of this work is to construct a small parameter set that can model a sequence- dependent equilibrium probability distribution for rigid base configurations of a DNA oligomer with any given sequence of any length. The model parameter sets previously available were for rigid base pair models ignoring all the couplings beyond nearest neighbour interactions. However it was shown in previous work, that this standard model of rigid base pair nearest neighbour interactions is inconsistent with a (then) large scale MD simulation of a single oligomer [36]. In contrast we here show that a rigid base nearest neighbour, dimer sequence dependent model is a quite good fit to many MD simulations of different duration and se- quence. In fact a hierarchy of rigid base models with different interaction range and length of sequence-dependence is discussed, and it is concluded that the nearest neighbour, dimer based model is a good compromise between accuracy and complexity of the model. A full parameter set for this model is estimated. An interesting feature is that despite the dimer dependence of the parameter set, due to the phenomenon of frustration, our model predicts non local changes in the oligomer shape as a function of local changes in the sequence, down to the level of a point mutation.

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