Studies of the outer membrane of gram-negative bacteria
Huang, Huey W.
Master of Science
The outer membranes of Gram-negative bacteria are highly asymmetric, with the inner leaflet composed of phospholipids and the outer leaflet mostly of lipopolysaccharides (LPS). The outer membrane is thought to act as a protective and permeability barrier, but is somehow permeable to various antimicrobial peptides. To study this problem we prepared oriented multilamellae of bilayers composed of pure LPS. X-ray diffraction showed that the samples produced good spectrum. The liquid crystalline to gel transition was observed by the appearance of a sharp peak corresponding to 4.23A and coexistence of two lamellar diffraction series. Phase diagrams of mutant LPS's were constructed as functions of temperature and the level of hydration. Electron density profiles were constructed, and compared with the program calculated model electron profiles, the peak position in the electron density profile was determined as the position of the phosphate atom in LPS molecule. Inorganic ions like Sodium(Na +), Potassium(K+), and Barium(Ba++) were added into the sample. Results showed that with the presence of the ions, the phase transition temperature of LPS mutant decreased, and the ions bound to the site where the phosphate atom located. Also, beta-sheet peptide protegrin-1 was added in the LPS sample. Results implied the peptide inserted in the headgroup of the LPS bilayer.
Microbiology; Molecular physics; Biology; Physics