ALTERED VOLTAGE SENSITIVITY OF MUTANT OMPC PORIN CHANNELS

Single OmpC porin channels have been reconstituted in planar bilayer m embranes, Wild-type OmpC forms trimers which are largely insensitive t o voltages below 250 mV.A single-point mutation of the ompC gene has b een prepared resulting in replacement of Trp56 by Cys in the eyelet re gion of the channel mall in a highly conserved segment of the polypept ide. The monomeric channels of which the trimer is composed have small er conductivity in 1 M NaCl (400 +/- 20 pS, mean and S.E.M., n = 30) a nd increased voltage sensitivity by comparison with the wild-type unde r similar conditions, whereas other (Dex) mutants form larger channels and display different behaviour, Further, by treatment in SDS solutio ns at different temperatures, the W56C mutant has been shown to be les s stable than either the wild-type or the Dex mutants.