Interaction of ω-conotoxin and the membrane calcium transport system of Escherichia coli


ω-Conotoxin, a calcium channel blocker, inhibits chemotaxis by Escherichia coli. To test whether ω-conotoxin acts at the cytoplasmic membrane, the kinetics of 125I-ω-conotoxin binding was investigated. 125I-ω-Conotoxin bound to Tris–EDTA-permeabilized cells or right-side-out membrane vesicles with saturation kinetics. Binding of 125I-ω-conotoxin to membrane vesicles was inhibited by Ca2+ ions, but not by Mg2+ ions. The calA mutant, defective in calcium transport, was more resistant to ω-conotoxin inhibition of chemotaxis than the parental wild-type. 125I-ω-Conotoxin binding to membrane vesicles indicated that both the wild-type and the calA mutant had similar KDs for ω-conotoxin binding. However, the saturation level was higher with the calA mutant, indicating that there are more binding sites in the calA mutant. Thus, calA does not directly affect the affinity of the ω-conotoxin binding site. Chemical cross-linking experiments identified two proteins as potential ω-conotoxin receptors.


Molecular, Cellular and Biomedical Sciences

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FEMS Microbiology Letters



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© 2000 Published by Elsevier B.V.