Single-molecule methods for ligand counting: linking ion uptake to DNA hairpin folding.
Ligand associations play a significant role in biochemical processes, typically through stabilizing a particular conformation of a folded biomolecule. Here, we demonstrate the ability to measure the changes in the number of ligands associated with a single, stretched biomolecule as it undergoes a conformational change. We do this by combining thermodynamic theory with single-molecule measurements that directly track biomolecular conformation. We utilize this technique to determine the changes in the ionic atmosphere of a DNA hairpin undergoing a force-destabilized folding transition. We find that the number of counterions liberated upon DNA unfolding is a nonmonotonic function of the monovalent salt concentration of the solution, contrary to predictions from common nucleic acid models. This demonstrates that previously unobserved phenomena can be measured with our ligand counting approach.
Materials Department and ‡BMSE Program, University of California , Santa Barbara, California 93106, United States.
Andrew
A
Dittmore
Jonathan
J
Landy
Adrian A
AA
Molzon
Omar A
OA
Saleh
D004247:DNA / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D055029:Inverted Repeat Sequences; D008024:Ligands; D009690:Nucleic Acid Conformation / Q000187:drug effects*; D013816:Thermodynamics
D008024:Ligands; D004247:DNA