The Effect of Lipopolysaccharides on the Electrostatic Properties of Gram-Negative General Porins from Enterobacteriaceae.

Abstract

We investigated, by using all-atom molecular dynamics simulations, the effect of the asymmetric outer membrane layer of Gram-negative bacteria, composed in the outer leaflet by polar/charged lipopolysaccharides (LPS), on the electrostatic properties of general porins from the Enterobacteriaceae family. These porins constitute the main path for the facilitated diffusion of polar antibiotics to cross the outer membrane. As model system we selected OmpK36 from Klebsiella pneumoniae, the ortholog of OmpC from Escherichia coli. This species presents high variability of amino acid composition of porins, with the effect to increase its resistance to the penetration of antibiotics. The various properties we analyzed seem to indicate that LPS acts as an independent layer without affecting the internal electrostatic properties of OmpK36. The only apparent effect at this time scale is the appearance of calcium ions, when present at moderate concentration in solution, inside the pore, though we noticed only increased fluctuations of the polarization density and slight changes on its average value.