Analysis of gating transitions among the three major open states of the OpdK channel

摘要

OpdK is an outer membrane protein of the pathogenic bacterium Pseudomonas aeruginosa. The recent crystal structure of this protein revealed a monomeric, 18-stranded β-barrel with a kidney-shaped pore, whose constriction features a diameter of 8 Å. Using systematic single-channel electrical recordings of this protein pore reconstituted into planar lipid bilayers under a broad range of ion concentrations, we were able to probe its discrete gating kinetics involving three major and functionally distinct conformations, in which a dominant open sub-state O2 is accompanied by less thermodynamically stable sub-states O1 and O3. Single-channel electrical data enabled us to determine the alterations in the energetics and kinetics of the OpdK protein when experimental conditions were changed. In the future, such a semi-quantitative analysis might provide a better understanding on the dynamics of current fluctuations of other β-barrel membrane protein channels.