title: Pf3 coat protein forms voltage-gated ion channels in planar lipid bilayers.
abstract: The coat protein of bacteriophage Pf3 forms discrete and stable ion channels of uniform size in planar bilayers of asolectin. Its primary sequence suggests a channel formed by a bundle of transmembrane helices. Since the apparent transmembrane region only consists of strongly hydrophobic residues, it represents a new class of channel-forming proteins. The channel activity is strongly voltage-dependent. The single-channel conductance of 60 pS (at 100 mV) in 0.2 M NaCl is slightly voltage-dependent, indicating conformational changes of the pore upon variation of the transmembrane electric field. The channel is unselective which suggests that the pore is of aqueous character. For the observed conductance, a channel diameter of 3.6 A is consistent with a tetrameric alpha-helix bundle, as calculated from a barrel-stave model. A pronounced dependence of the gating kinetics with increasing voltage arises from two opposing effects: an increase in the number of open channel structures, and a simultaneous, more than 3-fold decrease in the channel lifetime. Thus, a maximum activity is reached around 100 mV, a range which corresponds well with physiological membrane potentials. The channels activate only upon application of a positive voltage on the side of the membrane to which the protein had been added. The slow relaxation of the mean current upon application of sudden voltage jumps indicates a strong activation barrier in the channel gating process, which may result from the membrane translocation of the charged residues of the peptide ends. A channel-mediated import mechanism is suggested for the bacterial infection by phage DNA.
authors.affiliation: Institut de chimie physique II, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Pawlak
authors.forename: A
authors.initials: A
authors.lastname: Kuhn
authors.forename: H
authors.initials: H
authors.lastname: Vogel
mesh_terms: D000595:Amino Acid Sequence; D002213:Capsid / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D004553:Electric Conductivity; D017912:Inovirus / Q000378:metabolism*; D015640:Ion Channel Gating; D007473:Ion Channels / Q000737:chemistry / Q000378:metabolism*; D008051:Lipid Bilayers; D008564:Membrane Potentials; D008961:Models, Structural; D008969:Molecular Sequence Data; D010713:Phosphatidylcholines; D010743:Phospholipids; D011336:Probability
chemical_list: D007473:Ion Channels; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010743:Phospholipids; C024990:asolectin