Diameter of the mammalian porin channel in open and "closed" states: direct measurement at the single channel level in planar lipid bilayer

Porin isolated from bovine skeletal muscle was reconstituted in planar lipid bilayers under voltage clamp conditions. A set of non-electrolytes were used as molecular probes for determining the pore diameter. The maximal diameter of the open channel was estimated to be 3.02 + 0.26 nm. As observed for other porin channels, a large transmembrane potential drove the channel into a "closed" state. The channel transition to the low conductance (closed) state was followed by a decrease in the maximal diameter of the channel to 2.4 +- 0.08 nm.

Antigen F1 from yersinia pestis forms aqueous channels in lipid bilayer membranes

Antigen F1 is a protein of 17 kDa produced by Yersinia pestis it is cultured at 37 grade C. When incorporated into planar lipid bilayer membranes this protein induces fluctuations on membrane conductance typical of the formation of ionic channels. These fluctuations reveal two distinct unitary conductance sizes, one in the range of 800 to 1400 pS and the other in the range of 140 to 600 pS. Zero current potential measaurements in the presence of a salt gradient show that the channell is not significantly ion selective. The reversal potential measured in the presence of 0.5 MKCl on the cis side and 0.1 MKCl on the trans side was 3.58 ñ 3.98 mV (N=7). The non-selectivity of the channel, in addition to its large conductance, suggests that it forms large aqueous pores. The present results, taken together with other data showing that nantigen F1 inhibits the activity of phagocytic cells, suggest that antigen F1 acts by forming aqueous pores in the membrane of these target cells