Influence of the B-band O-antigen chain in the structure and electrostatics of the lipopolysaccharide membrane of Pseudomonas aeruginosa

Lipopolysaccharides (LPSs) form the major constituent of the outer membrane of Gram-negative bacteria, and are believed to play a key role in processes that govern microbial metal binding, surface adhesion, and microbe-mediated oxidation/reduction reactions. It is also a major causative agent of nosocomial illness, eliciting both chronic and acute infections in burn, immunocompromised, and cystic fibrosis. Phenotypic variation in the relative expression of A- and B-band in the LPS of Pseudomonas aeruginosa seems to alter its overall surface characteristics influencing adhesion and favoring survival. Classical molecular dynamics simulations of A-B+ LPS membrane model of P. aeruginosa were carried out in explicit solvent for 12+ ns. The B-band presents a remarkable flexibility remaining fully solvated and does not interact with the sugar units from the LPS core surface residues, in agreement with atomic force microscopy experiments. Comparison with previous simulations of the rough LPS membrane suggests that the presence of the B-band promotes membrane expansion. In addition, this O-antigen chain dramatically alters the electrostatic potential and surface charge of the LPS membrane. This is illustrated by the resulting electrostatic surface potential. These results are compared to previous simulations of the rough LPS and a model hypothesis is proposed to explain the increased ability of B-band expressing microorganisms to adhere to cell surfaces and the necessity of these organisms to loose the O side chain for the development of acute infections.