Membrane proteins represent 20 to 30% of the total cellular protein and are of special interest in the understanding of many diseases. Their characterization, however, still is a challenging task since their inherent hydrophobicity and high aggregation tendency complicates their biophysical and biochemical analysis. Methods that can be applied on soluble proteins are difficult to apply on membrane proteins. It is e.g. not described that membrane proteins can be straightforwardly used as targets for phage display. Phage display is a method that allows identification of peptide ligands for a target protein of choice. Since it is estimated that more than 50 % of all clinical drugs are targeted to membrane proteins, a phage display screening technique for transmembrane target proteins will help accelerate the drug development process.
In this project, we are using nanodiscs to reconstitute transmembrane proteins in a near native environment. Nanodiscs are small discoidal phospholipid bilayers that are encircled by two copies of an amphipatic helical protein called membrane scaffold protein (MSP) in a belt-like configuration. The advantages of nanodiscs compared to other membrane models are their defined size, their stability and the accessibility of the protein from both sides of the membrane. By far the most important advantage is that nanodisc-embedded transmembrane proteins can be treated and handled very much as globular soluble proteins.
The aim of this project is the establishment of a method to use transmembrane proteins as targets in phage display screening. Therefore, model membrane proteins and medically relevant transmembrane proteins will be incorporated into nanodiscs and used for phage display in order to select peptide ligands that bind to epitopes that are formed in the native membrane environment (e.g. loops). We used the well characterized membrane protein bacteriorhodopsin of Halobacterium salinarum as a model target protein to establish this method.
Pavlidou M, Hänel K, Möckel L, Willbold D: Nanodiscs Allow Phage Display Selection for Ligands to Non-Linear Epitopes on Membrane Proteins. PLoS ONE 9, e72272 (2013)