The effect of anti-Z-DNA antibodies on the B-DNA-Z-DNA equilibrium.
Four different preparations of rabbit and goat anti-Z-DNA antibodies were examined to determine the effects of antibody binding on the B-DNA-Z-DNA equilibrium. One of the four antibodies, a goat IgG, caused a marked lowering in the ionic strength required for the B-DNA to Z-DNA transition in poly(dG-dC) X poly(dG-dC), shifting the midpoint from 2.25 to 2.0 M NaCl. This IgG had a more prominent high affinity antibody population than did the other goat IgG, which caused little change in the midpoint of this transition. The presence of anti-Z-DNA antibodies also reduced the degree of negative supercoiling required for the formation of Z-DNA in (dG-dC)n sequences inserted into closed circular plasmid DNA. The goat IgG with the more marked effect on the salt-induced transition also had a greater effect in favoring Z-DNA formation in negatively supercoiled plasmids. A shift toward Z-DNA formation was observed in circular dichroism measurements upon antibody binding to poly(dG-dC) X poly(dG-dC) in very low ionic strength solution as well. We propose that the stabilization of Z-DNA by antibody binding in poly(dG-dC) X poly(dG-dC) occurs cooperatively, several antibody molecules binding to a single polymer molecule and stabilizing the entire molecule in Z-DNA through their combined binding energies. The stabilization of Z-DNA by antibody binding in a supercoiled plasmid can be significant, and failure to consider this effect and to choose appropriate conditions for measurement can lead to errors in estimating when Z-DNA will form in response to negative supercoiling.
E M
EM
Lafer
R
R
Sousa
R
R
Ali
A
A
Rich
B D
BD
Stollar
D000818:Animals; D000906:Antibodies; D004247:DNA / Q000276:immunology*; D004278:DNA, Superhelical / Q000378:metabolism; D006041:Goats / Q000276:immunology; D007074:Immunoglobulin G / Q000378:metabolism; D009690:Nucleic Acid Conformation / Q000187:drug effects; D009994:Osmolar Concentration; D010957:Plasmids; D011089:Polydeoxyribonucleotides / Q000378:metabolism; D011817:Rabbits / Q000276:immunology; D012965:Sodium Chloride / Q000494:pharmacology
D000906:Antibodies; D004278:DNA, Superhelical; D007074:Immunoglobulin G; D011089:Polydeoxyribonucleotides; C019530:poly(dC-dG); D012965:Sodium Chloride; D004247:DNA