Outer membrane of Pseudomonas aeruginosa: heat- 2-mercaptoethanol-modifiable proteins

Abstract

A number of polyacrylamide gel systems and solubilization procedures were studied to define the number and nature of major polypeptide bands in the outer membrane of P. aeruginosa. Five of the 8 major outer membrane proteins were heat modifiable in that their mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was determined by the solubilization temperature. Four of these heat-modifiable proteins had characteristics similar to protein II* of the Escherichia coli outer membrane. Addition of lipopolysaccharide subsequent to solubilization caused reversal of the heat modification. The other heat-modifiable protein, the porin protein F, was unusually stable to sodium dodecyl sulfate. Long periods of boiling in sodium dodecyl sulfate were required to cause conversion to the heat-modified form. This was demonstrated both with outer membrane-associated and purified lipopolysaccharide-depleted protein F. Furthermore, lipopolysaccharide treatment had no effect on the mobility of heat-modified protein F. Protein F represents a new class of heat-modifiable protein. The electrophoretic mobility of protein F was modified by 2-mercaptoethanol, and the 2-mercaptoethanol and heat modification of mobility were independent of one another. The optimal conditions for the examination of the outer membrane proteins of P. aeruginosa by 1-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis are discussed.