Lipopolysaccharide membranes and membrane proteins of pseudomonas aeruginosa studied by computer simulation

Pseudomonas aeruginosa is a ubiquitous environmental Gram-negative bacterium with high metabolic versatility and an exceptional ability to adapt to a wide range of ecological environments, including soil, marches, coastal habitats, plant and animal tissues. Gram-negative microbes are characterized by the asymmetric lipopolysaccharide outer membrane, the study of which is important for a number of applications. The adhesion to mineral surfaces plays a central role in characterizing their contribution to the fate of contaminants in complex environmental systems by effecting microbial transport through soils, respiration redox chemistry, and ion mobility. Another important application stems from the fact that it is also a major opportunistic human pathogen that can result in life-threatening infections in many immunocompromised patients, such as lung infections in children with cystic fibrosis, bacteraemia in burn victims, urinary-tract infections in catheterized patients, hospital-acquired pneumonia in patients on respirators, infections in cancer patients receiving chemotherapy, and keratitis and corneal ulcers in users of extended-wear soft contact lenses. The inherent resistance against antibiotics which has been linked with the specific interactions in the outer membrane of P. aeruginoso makes these infections difficult to treat. Developments in simulation methodologies as well as computer hardware have enabled the molecular simulation of biological systems of increasing size and with increasing accuracy, providing detail that is difficult or impossible to obtain experimentally. Computer simulation studies contribute to our understanding of the behavior of proteins, protein-protein and protein-DNA complexes. In recent years, a number of research groups have made significant progress in applying these methods to the study of biological membranes. However, these applications have been focused exclusively on lipid bilayer membranes and on membrane proteins in lipid bilayers. A few simulation studies of outer membrane proteins of Gram-negative bacteria have been reported using simple lipid bilayers, even though this is not a realistic representation of the outer membrane environment. This contribution describes our recent molecular Simulation studies of the rough lipopolysaccharide membrane of P. aeruginosa, which are the first and only reported studies to date for a complete, periodic lipopolysaccharide outer membrane. This also includes our current efforts in building on our initial and unique experience simulating the lipopolysaccharide membrane in the development and application of novel computational procedures and tools that allow molecular simulation studies of outer membrane proteins of Gram-negative bacteria to be carried out in realistic membrane models.