The oligopeptide permease (Opp) in£. cob consists of five proteins, OppABCDF. The periplasmic oligopeptide binding protein (OppA) acts as the initial receptor for the uptake of oligopeptides, and interacts with the integral membrane components (possibly just OppB and OppC) which form a channel through which the peptide passes. The other two membrane associated components, OppD and OppF couple ATP hydrolysis to peptide translocation. Genetic and biochemical evidence that support a role for the Asp300 of E. coli OppA in the interaction with the membrane components are presented in this study.
Two E.coli mutants PA0522 and PA0523 with a point mutation in OppA [Asp300~Ser]OppA and [Asp300~Arg]-OppA, respectively were used in this study. Both OppA mutant proteins have the ability to bind peptides. However, the oligopeptide permease system of these mutants is completely defective in peptide transport. It was concluded that the residue Asp-300 of E. coli, that is located at the surface of the oligopeptide binding protein (OppA), is intimately involved in the events that allow the translocation of the ligand from the OppA-ligand complex through the membrane associated components of
the oligopeptide permease.
Compensative mutants able to recover the oligopeptide permease function for the OppA defect were isolated. The characterisation of these mutants and their oligopeptide binding protein, indicated that the recovery of the oligopeptide permease activity most likely arose from changes in the membrane components. These results provide supportive evidence of the role of Asp300 in the interaction with the membrane components.