Chemistry

Polymer Dynamics in a Pore

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Science  17 Mar 2000:
Vol. 287, Issue 5460, pp. 1889
DOI: 10.1126/science.287.5460.1889e

Unlike ion channels, which usually are specific for cations or anions and are gated by voltage or small molecules, the α-hemolysin from Staphylococcus assembles to form relatively large transmembrane pores (tens of angstroms) that allow many types of molecules to pass freely across the lipid bilayer of a cell. Howorka et al. have derivatized the hemolysin monomer with synthetic polymers in an attempt to modify and control their porosity. When polyethylene glycol (PEG, of 5000 daltons) was attached to the inside of a single subunit, the heptameric pore could readily accommodate only one such subunit along with six of the wild type—additional PEG molecules apparently exceeded the volume of the pore's vestibule and interfered with assembly. Single-channel recordings showed fluctuations in low conductance states (with lifetimes of tens of seconds) that were attributed to occupancy of the vestibule by the polymer chain. High-amplitude conductance fluctuations (millisecond duration) were observed and attributed to the movement of the polymer chain into the narrower transmembrane channel. These modified pores could find use for studies of polymer dynamics and may find applications in biosensing.—PDS

J. Am. Chem. Soc., in press.

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