Mg2+ — Inner Sphere Complexes at “Ends” and “Bends” of Polynucleotides and their Potential Role as Long Range Inducers of Conformation Changes
A short review is given on Mg2+-binding to oligo- and polynucleotides with special emphasis on the formation of inner sphere complexes. Due to the rather slow exchange of ligands in the inner sphere of Mg2+ these complexes are localised at a given site with a relatively long lifetime, whereas outer sphere complexes are much more mobile (ion atmosphere binding). Measurements of the binding kinetics demonstrate that Mg2+ binds to polymers like poly(A) mainly in the form of outer sphere complexes, whereas short oligoriboadenylates are shown to form inner sphere complexes. Evidence is presented that the measured increase of the inner sphere binding constant with decreasing chain length results from preferential inner sphere complexation at chain ends. Inner sphere complexes are also formed at “bends” of polynucleotide chains. An example is given for the anticodon loop of tRNAPhe, where Mg2+ preferentially forms an inner sphere complex with one of two loop conformations. The special properties of Mg2+-ligands may be used for transmission of a “signal” along a polynucleotide chain.
KeywordsElectric Field Pulse Conformation Change Sphere Complex Hydration Sphere tRNA Molecule
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