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. 2010 May 5;98(9):1820–1829. doi: 10.1016/j.bpj.2010.01.010

Figure 2.

Figure 2

OmpU has a larger effective radius than OmpT. (A) Effect of penetrating PEGs on the OmpU trimer. The two traces were obtained from the same inserted trimer in planar lipid bilayer (150 mM KCl; pH 7.2), before and after adding PEG200 at a final concentration of 10.9% (w/w). The voltage was stepped from 0 to +70 mV. Note the decrease in the current level corresponding to the fully open trimer (level marked open). (B) Molecular weight dependence of the conductance ratio. The conductance ratio is the ratio of the fully open trimer conductance measured in the presence of PEG over the conductance measured without PEGs in the same bilayer. Each data point represents the average conductance ratio measured on two (no error bar) or three or more (error bar) independent experiments. The error bars represent the SE. The data obtained for OmpU (solid circles) and OmpT (open circles) were fitted to Eq. 1 in Materials and Methods. The molecular weight cut-offs (ω0) were found to be 916 ± 91 and 598 ± 65 for OmpU and OmpT, respectively. The corresponding effective radius for OmpU and OmpT are 0.55 nm and 0.43 nm, respectively. Other parameters obtained from the fits were: for OmpU: χ = 0.31 ± 0.03; α = 1.59 ± 0.36; (conductance ratio)max = 1.03 ± 0.01; and for OmpT: χ = 0.32 ± 0.03; α = 1.21 ± 0.24; (conductance ratio)max = 1.03 ± 0.01.