Stretching and unzipping nucleic acid hairpins using a synthetic nanopore

We have explored the electromechanical properties of DNA by using an electric field to force single hairpin molecules to translocate through a synthetic pore in a silicon nitride membrane. We observe a threshold voltage for translocation of the hairpin through the pore that depends sensitively on the diameter and the secondary structure of the DNA. The threshold for a diameter 1.5 < d < 2.3 nm is V > 1.5 V, which corresponds to the force required to stretch the stem of the hairpin, according to molecular dynamics simulations. On the other hand, for 1.0 < d < 1.5 nm, the threshold voltage collapses to V < 0.5 V because the stem unzips with a lower force than required for stretching. The data indicate that a synthetic nanopore can be used like a molecular gate to discriminate between the secondary structures in DNA

Production of antimicrobial films by incorporation of partially purified lysozyme into biodegradable films of crude exopolysaccharides obtained from Aureobasidium pullulans fermentation

WOS: 000234084600005Antimicrobial films were produced by incorporating partially purified lysozyme into films of crude exopolysaccharides (59 % pullulan) obtained from Aureobasidium pullulans fermentation. After film making, the films containing lysozyme at 100, 260, 520 and 780 mu g/cm(2) showed 23 to 70 % of their expected enzyme activities. The highest recovery of enzyme activity (65-70 %) after the film making was obtained in films prepared by incorporating lysozyme at 260 mu g/cm(2) (1409 U/cm(2)). The incorporation of disodium EDTA(.)2H(2)O and sucrose did not affect the initial lysozyme activity of the films significantly. With or without the presence of disodium EDTA(.)2H(2)O at 52 or 520 mu g/cm(2), lysozyme activity showed sufficient stability in the films during 21 days of cold storage. However, the presence of sucrose at 10 mg/cm(2) in the films caused the destabilization of part of enzyme activity (almost 35 %) at the end of storage. The combinational incorporation of lysozyme at 780 pg/cm(2) (4227 U/cm(2)) and disodium EDTA(.)2H(2)O at 520 mu g/cm(2) gave antimicrobial films effective on Escherichia coli. However, in the studied lysozyme concentration range the films did not show any antimicrobial activity against Lactobacillus plantarum. This study clearly showed that the partially purified lysozyme and crude exopolysaccharides from Aureobasidium pullulans may be used to obtain antimicrobial films to increase the safety of foods