Isolation and Characterization of Major Outer Membrane Proteins of Pseudomonas aeruginosa Strain PAO with Special Reference to Peptidoglycan-Associated Protein

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Abstract
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°C. At higher temperatures (>55°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 β-structure, while protein I was rich in α-helix. When isolated protein F was heated (100°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.