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J Phys Chem B. 2017 Jan 26;121(3):451-462. doi: 10.1021/acs.jpcb.6b08764. Epub 2017 Jan 17.

Computational Assessment of Potassium and Magnesium Ion Binding to a Buried Pocket in GTPase-Associating Center RNA.

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  • 1Department of Medicinal Chemistry, College of Pharmacy, The University of Utah , 2000 East 30 South Skaggs 307, Salt Lake City, Utah 84112-5820, United States.
  • 2Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine , St. Louis, Missouri 63110, United States.

Abstract

An experimentally well-studied model of RNA tertiary structures is a 58mer rRNA fragment, known as GTPase-associating center (GAC) RNA, in which a highly negative pocket walled by phosphate oxygen atoms is stabilized by a chelated cation. Although such deep pockets with more than one direct phosphate to ion chelation site normally include magnesium, as shown in one GAC crystal structure, another GAC crystal structure and solution experiments suggest potassium at this site. Both crystal structures also depict two magnesium ions directly bound to the phosphate groups comprising this controversial pocket. Here, we used classical molecular dynamics simulations as well as umbrella sampling to investigate the possibility of binding of potassium versus magnesium inside the pocket and to better characterize the chelation of one of the binding magnesium ions outside the pocket. The results support the preference of the pocket to accommodate potassium rather than magnesium and suggest that one of the closely binding magnesium ions can only bind at high magnesium concentrations, such as might be present during crystallization. This work illustrates the complementary utility of molecular modeling approaches with atomic-level detail in resolving discrepancies between conflicting experimental results.

PMID:
27983843
PMCID:
PMC5278497
DOI:
10.1021/acs.jpcb.6b08764
[PubMed - in process]
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