Structure and function of substrate-binding proteins of ABC-transporters

This thesis explores the connection between structure and function of substrate-binding proteins. A large part of the work covers the oligopeptide-binding protein OppA, which originates from the milkbacteria Lactococcus lactis. OppA is a part of the ABC-transporter oligopeptide permease, with the name of Opp. L. lactis lives in milk, and to survive the bacteria needs to import nutritious substances. Opp plays a role in this, as it imports peptides from α-, β- en κ-caseine (small parts of milkproteins which has been cut in pieces). OppA is sitting on the outside of the cell, attached to the cellmembrane, and functions as the initial receptor for these peptides. After binding a peptide, OppA transfers it to the part of Opp that is located within the cellmembrane, which subsequently transfers the peptide to the inside of the cell. Multiple crystal structures of OppA were determined in this thesis, both with and without bound peptide. On the basis of those structures a new model was presented that explains how OppA can bind these peptides. The proof of that model was later delivered in the form of another structure, together with further biochemical charactarization. A structure of another protein was also determined, that of OpuAC. OpuAC is a part of an ABC-transporter that imports glycine betaine to prevent osmotic pressure. During the research, it became necessary to be able to incorporate selenomethionine into proteins produced in Lactococcus lactis, and a method for this was developed.