Physical mechanisms of bacterial survival revealed by combined grazing incidence x-ray scattering and Monte Carlo simulations

RAFAEL GUSTAVO OLIVEIRA; SCHNECK, E.; QUINN, B. E.; KONOVALOV, O. E.; BRANDENBURG, K.; SEYDEL, U.; GILL, T.; HANNA, C. B.; PINK, D. A.; TANAKA, M.

COMPTES RENDUS CHIMIE

Elsevier

Lugar: version impresa enero 2009, version online noviembre 2008; Año: 2008 vol. 12 p. 209 - 209

1631-0748

he combination of grazing-incidence X-ray scattering experiments and Monte Carlo simulation unravels the physics of bacterial survival against cationic antimicrobial peptides (protamine). As a realistic model of bacterial outer membranes, an insoluble monolayer of lipopolysaccharide from Salmonella enterica sv. Minnesota Ra (LPS Ra) is spread on buffered subphase. In the presence of Ca2+, vertical electron density profiles reconstructed from X-ray scattering imply the "collapse" of saccharide chains, suggesting that Ca2+ bridges the negatively charged saccharide units. Under this condition, the LPS monolayer remains intact even after injection of protamine near the minimum inhibitory concentration. This can theoretically be accounted in terms of the formation of an electrostatic energy barrier that prevents the approach of protamine to the  ydrophobic region. In contrast, as predicted from in vivo experiments, the intrusion of protamine in the absence of Ca2+ results in the complete d