Conversion of OprO into an OprP-like Channel by Exchanging Key Residues in the Channel Constriction.

Under phosphate-limiting conditions, the channels OprP and OprO are induced and expressed in the outer membrane of Pseudomonas aeruginosa. Despite their large homology, the phosphate-specific OprP and the diphosphate-specific OprO pores show structural differences in their binding sites situated in the constriction region. Previously, it was shown that the mutation of amino acids in OprP (Y62F and Y114D) led to an exchange in substrate specificity similar to OprO. To support the role of these key amino acids in the substrate sorting of these specific channels, the reverse mutants for OprO (F62Y, D114Y, and F62Y/D114Y) were created in this study. The phosphate and diphosphate binding of the generated channels was studied in planar lipid bilayers. Our results show that mutations of key residues indeed reverse the substrate specificity of OprO to OprP and support the view that just a few strategically positioned amino acids are mainly responsible for its substrate specificity.