Infoscience

Journal article

Pf3 coat protein forms voltage-gated ion channels in planar lipid bilayers

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 helixes. 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 elec. field. The channel is unselective which suggests that the pore is of aq. character. For the obsd. conductance, a channel diam. of 3.6 .ANG. is consistent with a tetrameric a-helix bundle, as calcd. from a barrel-stave model. A pronounced dependence of the gating kinetics with increasing voltage arises from two opposing effects: an increase in the no. of open channel structures, and a simultaneous, more than 3-fold decrease in the channel lifetime. Thus, a max. activity is reach around 100 mV, a range which corresponds well with physiol. membrane potentials. The channels activate only upon application of a pos. 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. [on SciFinder (R)]

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