title: Surface-lattice model describes electrostatic interactions of ions and polycations with bacterial lipopolysaccharides: ion valence and polycation's excluded area.
abstract: The bacterial outer membrane (OM) is compositionally distinct and contains polyanionic lipopolysaccharide (LPS) in the outer layer as a main component. It has long been known that the cation-binding ability of LPS is one of the key determinants of OM permeability. Here we present a two-dimensional lattice model of the outer LPS layer, in which the lattice is decorated with bound ions or polycations; while small ions can occupy single binding sites, polycations, modeled as (charged) rods, compete for binding sites through their area exclusion, a consequence of their multisite binding. Our results suggest that in the parameter space of biological relevance, the effect of area exclusion is well-reflected in the competitive binding of Mg(2+) and polycations onto LPS; by reducing the apparent binding affinity of polycations, it enhances Mg(2+) binding. Despite simplifications, our results are generally consistent with the common view of Mg(2+) as OM-stabilizing and polycations as OM-perturbing agents. They will be useful for understanding how cationic antimicrobials can gain entry into the cytoplasmic membrane. We also outline a few strategies for extending our model toward a more realistic modeling of OM permeability.
authors.affiliation: Department of Physics and Astronomy, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Norman H
authors.initials: NH
authors.lastname: Lam
authors.forename: Bae-Yeun
authors.initials: BY
authors.lastname: Ha
mesh_terms: D001419:Bacteria / Q000737:chemistry*; D008070:Lipopolysaccharides / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry*; D008958:Models, Molecular; D011073:Polyamines / Q000737:chemistry*; D000071228:Polyelectrolytes; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D008070:Lipopolysaccharides; D008274:Magnesium; D011073:Polyamines; D000071228:Polyelectrolytes