Restriction endonucleases (REs) cleave DNA at specific site in presence of Mg ion. Experiments further emphasize the role of hydration in metal ion specificity and sequence specificity of DNA cleavage. However, the relation between hydration and specificity has not been understood till date. This leads us to study via all-atom molecular dynamics (MD) simulations how the hydration around the scissile phosphate group changes in presence of Mg and Ca and depend on the DNA sequence. We observe the least number of hydrogen bonds around the scissile phosphate group in presence of Mg ion. We further find that the hydrogen bonds decrease at the scissile phosphate on mutating one base pair in the cleavage region of the DNA in Mg loaded EcoRI-DNA complex. We also perform steered MD simulations and observe that the rate of decrease of fraction of hydrogen bonds is slower in the mutated complex than the unmutated complex.
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