Electrostatic versus nonelectrostatic effects in DNA sequence discrimination by divalent ions Mg2+ and Mn2+.

Area of Science:

• Biochemistry
• Computational Chemistry
• Enzymology

Background:

• Magnesium (Mg2+) and Manganese (Mn2+) ions are essential cofactors for phosphoryl transfer enzymes, including restriction endonucleases.
• These metal ions play crucial roles in enzymatic catalysis but exhibit significant differences in substrate specificity, with Mg2+ showing higher sequence discrimination than Mn2+.

Purpose of the Study:

• To investigate the fundamental differences in the electronic structures of nucleobase-hydrated-metal ion complexes that lead to the contrasting selectivity of Mg2+ and Mn2+.
• To elucidate the impact of metal ion binding sites, complex geometry, and solvation effects on enzyme substrate specificity.

Main Methods:

• Density Functional Theory (DFT) and second-order Møller-Plesset (MP2) calculations were employed to determine the structures and interaction energies of Mg2+ and Mn2+ complexes with nucleobases.
• Analysis of binding sites, geometric distortions, charge transfer, and electrostatic interactions was performed.

Main Results:

• Both Mg2+ and Mn2+ ions prefer similar binding sites, but Mn2+ complexes display greater geometric distortions and variability compared to Mg2+ systems.
• In gas-phase inner-shell complexes, Mg2+ is preferred due to nonelectrostatic effects, while interaction energies are similar in outer-shell complexes.
• Solvation effects amplify nucleobase preferences, and electrostatic properties significantly influence metal ion selectivity, with Mn2+ generally facilitating base substitutions more readily.

Conclusions:

• The contrasting selectivity of Mg2+ and Mn2+ in enzymes arises from the inherent flexibility of Mn2+ complexes, leading to increased polarization and charge-transfer effects.
• Differences in solvation and electrostatic interactions further contribute to the distinct nucleobase preferences and overall enzyme function modulated by these metal ions.