Ionophore properties of OmpA of Escherichia coli.

Both porins OmpA1, from wild-strain K12 Escherichia coli, and OmpA2, from a K12 derivative deficient in both OmpF and OmpC, are able to form ion channels in virtually solvent-free membranes. The conductance has been shown to vary in a discrete fashion with different single increment values especially with OmpA2. This behaviour seems to indicate, beside monomers, the presence of aggregates of different sizes. The estimated small pore diameter (0.6-0.7 nm) for the monomeric would explain the weak permeability of this narrow channel toward different solutes. OmpA protein, from experiments of ion selectivity and zero-current potential, is determined weakly anion selective.