Metal binding to phosphate

Figure H shows experiments in which metals bind to phosphates and bases simultaneously—i.e., degradation (at pH 7) of the polynucleotides by zinc in the presence of silver ion. Silver inhibits the degradation of Poly A and Poly C, which do not readily react strongly with silver.

The stabihzation of DNA by metal binding to phosphate is a phenomenon that has been known for a long time (7, 8). It stems from the fact that DNA, devoid of bound metals, contains an array of negatively charged phosphate ions on its surface that tend to repel each other. Therefore, when DNA is dissolved in distilled water, it spontaneously unwinds because these negative charges want to get as far away from... 

Figure 15. Stabilization of ordered structure by metals binding to phosphate...

In contrast to the relatively simple structures incorporating one of the first three binding motifs, the polymeric complex [Cu3(5 -GMP)3(H20)8] has three distinct coordination environments about different Cu + ions. While this complex is unusually sophisticated, the polymeric nature of the material is common for many metal complexes with GMP or IMP, in which inner-sphere binding occurs to both the N-7 atom and phosphate oxygens of a single nucleotide residue, but does not involve the same metal ion. As described in Section 5.5, there are also unusual structures ( open complexes ) of Cu + species and GMP, which involve only inner-sphere metal binding to the phosphate group. 

It is immediately apparent that there are two very different kinds of sites for metal coordination available on an RNA and DNA molecule—i.e., (1) the phosphate groups on the sugar phosphate backbone and (2) the oxygen and nitrogen donor atoms on the bases." We shall first discuss the consequences of binding to phosphate. 

I should like now to discuss some of the consequences for the ligands of metals binding to the bases and to the phosphate groups of the macromolecules. 

The Lewis-acidic uranyl dication, UOi, center has been used by Reinhoudt and his group to build up receptors based on uranyl-salen complexes and crown ether units, 12. In particular, the two benzo[15]crown-5 units form a sandwich-like complex with potassium while the metal binds to the dihydrogen phosphate counterion. ... 

Metal ions bind to both phosphate and base sites on the nucleic acid molecules, and each type of binding results in characteristic ligand reactions. Many metals bind to both types of sites. Among these is zinc(II), and we shall therefore concentrate our attention on the interactions of this metal ion with nucleic acids. 

D-Serine dehydrase from both E. coli and Neurospora required pyridoxal phosphate as a coenzyme. In contrast to L-serine dehydrase, threonine is attacked very poorly by the D-enz3une. Magnesium ions had no activating affect on the E. coli enzyme, but it partially reversed the inhibition caused by the metal-binding reagents, phosphate, citrate, cysteine, cyanide, and 8-hydroxyquinoline of the Neurospora enzyme. ... 

Certain kinds of metal ions bind to the DNA double strands by an electrostatic interaction with the phosphate group(s) or by complex formation with the sugar moiety or the nucleic... 

---