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

PhD ceremony: Mr. R.P.A. Berntsson, 13.15 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: Structure and function of substrate-binding domains of ABC-transporters

Promotor(s): prof. B. Poolman, prof. D.J. Stolboom

Faculty: Mathematics and Natural Sciences

The thesis of Ronnie Berntsson explores the connection between structure and function of substrate-binding proteins. A large part of his 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 cell membrane, 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 by Berntsson, both with and without bound peptide. On the basis of those structures he has presented a new model that explains how OppA can bind these peptides. The proof of that model he has delivered later in the form of another structure, together with further biochemical charactarization. A structure of another protein was also determined by Berntsson, 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 L. lactis, and a method was developed by him that made this possible.