Functional characterization of Pseudomonas fluorescens OprE and OprQ membrane proteins

Outer membrane (OM) proteins of the OprD family may enable bacteria of the genus Pseudomonas to adapt to various environments by modulating OM permeability. The OprE and OprQ porins from P. fluorescens strain MF0 were purified and identified by MALDI-TOF mass spectrometry and N-terminal and internal microsequencing. These proteins, when reconstituted in an artificial planar lipid bilayer, induced similar ion channels with low single-conductance values. Secondary structure prediction of both proteins showed similar folding patterns into a 16 transmembrane β-strands barrel but a highly variable amino-acid composition and length for their putative external loops implicated in porin function. Both proteins were overexpressed under poor oxygenation conditions, but not by using several amino acids as sole carbon source, indicating a different specificity for these proteins compared to the paradigm of this protein family, OprD.