Isolation and characterization of major outer membrane proteins of Pseudomonas aeruginosa strain PAO with special reference to peptidoglycan-associated protein.

The outer membrane of Pseudomonas aeruginosa PAO contains six major proteins (proteins D, E, F, G,H, and I). Two of them (protein F and protein H) were found to be retained by the peptidoglycan layer when cell envelopes were extracted with 2% sodium dodecyl sulfate (SDS) solution at 35 degrees C. At higher temperature (greater than 55 degrees C), no proteins were retained by peptidoglycan. By making use of this property, purification of protein F and protein H was achieved. Three other major outer membrane proteins, D, E, and I were also isolated and characterized. Their amino acids compositions were determined. Circular dichroism spectra of these isolated proteins were measured in SDS solution. Protein F was rich in beta-structure, while protein I was rich in alpha-helix. When isolated protein F was heated (100 degrees C-15 min) in SDS solution, the circular dichroism spectrum changed significantly. In parallel with the conformational change, the electrophoretic mobility of protein F on urea-SDS polyacrylamide gel also changed. These results indicate that protein F is a so-called heat-modifiable protein.