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J Phys Chem Lett. 2019 Dec 19;10(24):7937-7941. doi: 10.1021/acs.jpclett.9b03084. Epub 2019 Dec 11.

Experimental Evidence of Solvent-Separated Ion Pairs as Metastable States in Electrostatic Interactions of Biological Macromolecules.

Author information

1
Department of Biochemistry & Molecular Biology, Sealy Center for Structural Biology & Molecular Biophysics , University of Texas Medical Branch , Galveston , Texas 77555-1068 , United States.

Abstract

Electrostatic interactions via ion pairs are vital for biological macromolecules. Regarding the free energy of each ion pair as a function of the interionic distance, continuum electrostatic models predict a single energy minimum corresponding to the contact ion-pair (CIP) state, whereas atomically detailed theoretical hydration studies predict multiple energy minima corresponding to the CIP and solvent-separated ion-pair (SIP) states. Through a statistical analysis of high-resolution crystal structures, we present experimental evidence of the SIP as a metastable state. The histogram of interionic distances between protein side-chain NH3+ and DNA phosphate groups clearly shows two major peaks corresponding to the CIP and SIP states. The statistical data are consistent with the probability distribution of the CIP-SIP equilibria previously obtained with molecular dynamics simulations. Spatial distributions of NH3+ ions and water molecules around phosphates reveal preferential sites for CIP and SIP formations and show how the ions compete with water molecules.

PMID:
31809050
PMCID:
PMC6936746
[Available on 2020-12-19]
DOI:
10.1021/acs.jpclett.9b03084
[Indexed for MEDLINE]

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