Meningococcal PorA/C1, a channel that combines high conductance and high selectivity

ABSTRACT Class 1 porins (PorA/C1) from Neisseria meningitidis achieve both high selectivity and high conductance. The channel is highly selective (24:1 Na+ over CI^sup -^), suggesting a highly negatively charged selectivity filter. The trimeric nature of PorA/C1 accounts for part of the enormous conductance in 200 mM NaCI (0.97nS). However, the currents that can be achieved exceed the simple infinite-sink calculation for a pore 0.7 nm in radius (estimated from nonelectrolyte permeability). The conductance is linear with salt activity from 20 mM to 2.0 M NaCI with no sign of saturation at low salt. Impermeant polymers reduce the conductance in a manner consistent with their ability to …