Recognition of Z-RNA and Z-DNA Determinants by Polyamines in Solution: Experimental and Theoretical Studies

TLDR: Both theoretical and experimental studies indicate that polyamines can specifically recognize Z-helical determinants in solution as well as in crystals.

Abstract: Protonated polyamines are among the most efficient cations that induce the left-handed Z-form in certain polynucleotides. It is not known, however, whether these cations bind to specific sites on Z-sequences in solution. We have studied potential polyamine binding sites by measuring the effects of polyamines on the binding of purified immunoglobulins (IgGs) to different regions of the Z-helix and by molecular mechanics modeling. The specific binding of anti-Z-DNA and anti-Z-RNA IgGs to Z-helices was studied as a function of spermidine or spermine concentration. The effect of polyamines on the antibody-nucleic acid interaction was different for lgGs with different specificities for various determinants on the Z-helix. Polyamines inhibit the binding of certain anti-Z IgGs directed against specific sites probably at or near the interface between the major convex surface and the phosphate backbone, most likely by competing with the antibody binding site(s). In contrast, polyamines have no effect on o...