Aspartate: An interesting model for analyzing dipole-ion and ion pair interactions through its oppositely charged amine and acid groups |
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Authors: | Belén Hernández Fernando Pflüger Mahmoud Ghomi |
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Institution: | 1. Laboratoire Matrice Extracellulaire et Dynamique Cellulaire (MEDyC), UMR 7369, Université de Reims, Faculté des Sciences, Moulin de la Housse, Reims Cedex 2, France
Université Sorbonne Paris Nord, UFR Santé-Médecine-Biologie Humaine, Groupe de Biophysique Moléculaire, Bobigny Cedex, France;2. Université Sorbonne Paris Nord, UFR Santé-Médecine-Biologie Humaine, Groupe de Biophysique Moléculaire, Bobigny Cedex, France;3. Laboratoire Matrice Extracellulaire et Dynamique Cellulaire (MEDyC), UMR 7369, Université de Reims, Faculté des Sciences, Moulin de la Housse, Reims Cedex 2, France |
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Abstract: | Anionic species of aspartic acid, Asp−, having a zwitterionic backbone and a deprotonated side chain, appears to be a good example for analyzing dipole-ion and ion pair interactions. Density functional theory calculations were herein performed to investigate the low energy conformers of Asp− embedded in a dielectric continuum modeling an aqueous environment, through a scan of the potential energy as a function of the side chain (χ1, χ2) torsion angles. The most energetically favorable conformers having g+g− and g−g+ side chain orientations are found to be stabilized by charge-enhanced intramolecular H-bonding involving the positively charged () and the two negatively charged (COO−) groups. These conformers were further used to analyze Asp− + nW clusters (W: water, n = 1 or 3), and Asp−/Asp− pair formation. COO− groups were found to be the most attractive sites for hosting a water molecule (binding energy: −6.0 ± 1.5 kcal/mol), compared to groups (binding energy: −4.7 ± 1.1 kcal/mol). Energy separation between g+g− and g−g+ conformers increases upon explicit hydration. Asp−/Asp− ion pairs, stabilized by the interaction between the group of a partner and the COO− group of the other, shows a quite constant binding energy (−8.1 ± 0.2 kcal/mol), whatever the pair type, and the relative orientation of the two interacting partners. This study suggests a first step to achieve a more realistic image of intermolecular interactions in aqueous environment, especially upon increasing concentration. It can also be considered as a preliminary attempt to assess the interactions of the Lys+…Asp−/Glu− ion pairs stabilizing intra- and interchain interactions in proteins. |
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Keywords: | aspartic acid charge-enhanced H-bonding density functional theory calculations dipole-ion interactions energy landscape hydration ion pair interactions |
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