title: Melting of the solvent structure around a RNA duplex: a molecular dynamics simulation study.
abstract: From three 2.4-ns molecular dynamics simulations of the r(CpG)(12) duplex conducted at 5, 25 and 37 degrees C, a strong temperature dependence of the dynamics of the water molecules and ions located in the first nucleic acid coordination shell is observed. At 5 degrees C, the highest residence times of bound water molecules exceed 1 ns while, at 37 degrees C, they decrease to 0.5 ns in agreement with available NMR data. Similar temperature dependencies are observed for the potassium ions bound to the duplex. In this temperature range, the structure of the RNA helix remains essentially unchanged. Thus, the observed alterations correspond to a 'premelting' of the solvent structure around the duplex. It is proposed that, before the nucleic acid structure melts, the entropy of the solvent increases to a point where it is no longer compensated by the enthalpic contribution of solute-solute and solute-solvent interactions. At this stage, the weakest structural elements start to melt. In other terms, the experimentally observed melting processes are preceded by a melting of the more labile solvent structure.
authors.affiliation: Institut de Biologie Moléculaire et Cellulaire du CNRS, Modélisations et Simulations des Acides Nucléiques, UPR 9002, 15 rue René Descartes, 67084, Strasbourg Cedex, France. p.auffinger@ibmc.u-strasbg.fr
authors.forename: Pascal
authors.initials: P
authors.lastname: Auffinger
authors.forename: Eric
authors.initials: E
authors.lastname: Westhof
mesh_terms: D003198:Computer Simulation; D019277:Entropy; D008958:Models, Molecular; D015394:Molecular Structure; D009038:Motion; D009690:Nucleic Acid Conformation; D012330:RNA, Double-Stranded / Q000737:chemistry*; D012997:Solvents / Q000737:chemistry / Q000378:metabolism; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000737:chemistry* / Q000378:metabolism
chemical_list: D012330:RNA, Double-Stranded; D012997:Solvents; D014867:Water