Structure-Function Relationship of the Ion Channel Formed by Diphtheria Toxin in Vero Cell Membranes

Structure-Function Relationship of the Ion Channel Formed by Diphtheria Toxin in Vero Cell Membranes Diphtheria toxin (DT) forms cation selective channels at low pH in cell membranes and planar bilayers. The channels formed by wild-type full length toxin (DT-AB), wild-type fragment B (DT-B) and mutants of DT-B were studied in the plasma membrane of Vero cells using the patch-clamp technique. The mutations concerned certain negatively charged amino acids within the channel-forming transmembrane domain (T-domain). These residues might interact electrostatically with cations flowing through the channel, and were therefore exchanged for uncharged amino acids or lysine. The increase in whole-cell conductance induced by toxin, Δg m , was initially determined. DT-AB induced a ∼10-fold lower Δg m than DT-B. The mutations DT-B E327Q, DT-B D352N and DT-B E362K did not affect Δg m , whereas DT-B D295K, DT-B D352K and DT-B D318K drastically reduced Δg m . Single channel analysis of DT-B, DT-AB, DT-B D295K, DT-B D318K and DT-B E362K was then performed in outside-out patches. No differences were found for the single-channel conductances, but the mutants varied in their gating characteristics. DT-B D295K exhibited only a very transient channel activity. DT-AB as well as DT-B D318K displayed significantly lower open probability and mean dwell times than DT-B. Hence, the lower channel forming efficiency of DT-AB and DT-B D318K as compared to DT-B is reflected on the molecular level by their tendency to spend more time in the closed position and the fast flickering mode. The Journal of Membrane Biology Springer Journals

Structure-Function Relationship of the Ion Channel Formed by Diphtheria Toxin in Vero Cell Membranes

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Copyright © Inc. by 1997 Springer-Verlag New York
Life Sciences; Biochemistry, general; Human Physiology
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