Pseudomonas aeruginosa is one of the major cause of nosocomial infections around the word for its high capability to resist against antibiotic treatment. Its strong chemical barrier relies on a narrow and substrate specific set of channels in the outer membrane for the acquisition of nutrients and metabolites.
OprP and OprO are outer membrane porins of P. aeruginosa, they are organized as homotrimers of polypeptide subunits. The monomers share an elevated sequence homology and are involved in high affinity uptake of monophosphates and oligophosphates under phosphate starvation conditions. Their structure can be divided in three different regions: the extracellular cavity with the arginine path, the central core with the binding site and the periplasmic cavity with the lysine cluster, all together they form a hourglass-shaped tunnel per monomer where the positively charged column of basic residues directs the phosphates through the channel.
It has been demonstrated that OprO and OprP are highly induced during infections when the bacterium is in contact with lung epithelial cells. The expression of OprO increases by 145 folds whereas that of OprP increases by 10, so using them as specific uptake way for phosphonates antibiotics, can counteract the infection at the very beginning through a favourable route.
Fosfomycin and fosmidomycin are well studied phosphonate antibiotics active against both bacteria and protozoa. During my PhD work I focused not only on the analysis of the translocation of these antibiotics through OprO and OprP, but also on the study of the ion flux through these two porins via their reconstitution into artificial lipid bilayers of wild type proteins and mutants of the lysine cluster.
The characterization of the ion pathway across any channel is the first step for understanding its permeability properties and to design a new generation of molecules that can selectively go through them.