title: Frequency and effect of the binding of Mg2+, Mn2+, and Co2+ ions on the guanine base in Watson-Crick and reverse Watson-Crick base pairs.
abstract: We performed MP2 calculations to elucidate the structure and energetics of the Mg(2+), Mn(2+), and Co(2+) hexahydrated aquaions, and the effect of the metal binding to the N7 atom of (i) a single guanine, (ii) a guanine involved in a Watson-Crick pair, and (iii) a guanine involved in a reverse Watson-Crick base pair. Our comparative analysis of the three aquaions indicates a clear inverse correlation between the radius of the cation and the binding energy, that indeed increases in the order Mn(2+) < Co(2+) < Mg(2+). The trend in the binding energies of the pentahydrated cations to the N7 atom of the guanine is instead Mg(2+) < Mn(2+) < Co(2+), suggesting a rather different bonding scheme that, for the two transition metals, involves back-donation from the aromatic ring of the guanine to their empty d orbitals. In the gas phase, the three hydrated metals significantly stabilize both G-C base pair geometries, Watson-Crick and reverse Watson-Crick, we investigated. Inclusion of a continuous solvent model, however, remarkably reduces this additional stabilization, which becomes almost negligible in the case of the Mg(2+) cation coordinated to the guanine in the standard Watson-Crick geometry. Conversely, all three metal ions sensibly stabilize the reverse Watson-Crick geometry, also in water. Our results are supported by a screening of the structures available in the Protein Data Bank, which clearly indicates that the two transition metals we investigated have a tendency greater than Mg(2+) to coordinate to the N7 atom of guanines, and that there is no clear correlation between the number of guanines in experimental structures with a metal bound to N7 atom and their involvement in Watson-Crick base pairs.
authors.affiliation: Dipartimento di Scienze Applicate, Università di Napoli Parthenope, I-80143 Naples, Italy.
authors.forename: Romina
authors.initials: R
authors.lastname: Oliva
authors.forename: Luigi
authors.initials: L
authors.lastname: Cavallo
mesh_terms: D020029:Base Pairing; D001665:Binding Sites; D003035:Cobalt / Q000737:chemistry*; D006147:Guanine / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry*; D008345:Manganese / Q000737:chemistry*; D008968:Molecular Conformation; D013816:Thermodynamics
chemical_list: D007477:Ions; D003035:Cobalt; D008345:Manganese; D006147:Guanine; D008274:Magnesium