Sequence-dependent gating of an ion channel by DNA hairpin molecules

DNA hairpins produce ionic current signatures when captured by the alpha-hemolysin nano-scale pore under conditions of single molecule electrophoresis. Gating patterns produced by individual DNA hairpins when captured can be used to distinguish differences of a single base pair or even a single nucleotide [Vercoutere,W.A. et al. (2003) Nucleic Acids Res., 31, 1311-1318]. Here we investigate the mechanism(s) that may account for the ionic current gating signatures. The ionic current resistance profile of conductance states produced by DNA hairpin molecules with 3-12 bp stems showed a plateau in resistance between 10 and 12 bp, suggesting that hairpins with 10-12 bp stems span the pore vestibule. DNA hairpins with 9-12 bp stems produced gating signatures with the same relative conductance states. Systematic comparison of the conductance state dwell times and apparent activation energies for a series of 9-10 bp DNA hairpins suggest that the 3' and 5' ends interact at or near the limiting aperture within the vestibule of the alpha-hemolysin pore. The model presented may be useful in predicting and interpreting DNA detection using nanopore detectors. In addition, this well-defined molecular system may prove useful for investigating models of ligand-gated channels in biological membranes.