The amino terminus of Pseudomonas aeruginosa outer membrane protein OprF forms channels in lipid bilayer membranes: Correlation with a three-dimensional model

Pseudomonas aeruginosa OprF forms 0.36-nS channels and, rarely, 2- to 5-nS channels in lipid bilayer membranes. We show that a protein comprising only the N-terminal 162-amino-acid domain of OprF formed the smaller, but not t he larger, channels in lipid bilayers. Circular dichroism spectroscopy indi cated that this protein folds into a beta-sheet-rich structure, and three-d imensional comparative modeling revealed that it shares significant structu ral similarity with the amino terminus of the orthologous protein Escherich ia coli OmpA, which has been shown to form a beta-barrel. OprF and OmpA sha re only 15% identity in this domain, yet these results support the utility of modeling such widely divergent beta-barrel domains in three dimensions i n order to reveal similarities not readily apparent through primary sequenc e comparisons. The model is used to further hypothesize why porin activity differs for the N-terminal domains of OprF and OmpA.