How amino acids control the binding of Cu(II) ions to DNA .1. The role of the hydroxyl group of serine and threonine in fixing the orientation of the complexes

ESR data have been obtained on some hydrated copper(II) and copper(II) amino acid complexes bound to highly oriented DNA fibers. The complexes bind with random orientation on A-form DNA, while some of them bind stereospecifically on B-form DNA. The hydrated copper(II) ions bind to at least two different sites on B-form DNA at room temperature; one site is so mobile that the orientations of the complex fluctuate dynamically, while the other site fixes the orientation of the bound ions such that the angle between the g(parallel to) axis and the DNA helical axes becomes ca. 55 degrees. The g(parallel to) axis of glycine complex on B-form DNA at room temperature is aligned parallel to the fiber axis with large fluctuations in the orientation. L-serine and L-threonine fix the g(parallel to) axes of some of the complexes parallel to the fiber axes, indicating that the hydroxyl groups work as linkers to bind the complexes stereospecifically to B-form DNA. The hydroxyl groups in D-isomers do not work as L-isomers. (C) 1996 Elsevier Science Inc.