Crystal structures of wild-type AdiC in the presence and absence of the substrate agmatine at 2.6-Å and 2.2-Å resolution.
Please see our recent publication: Ilgü et al. (2016), Proc. Natl. Acad. Sci. USA
Membrane proteins fulfill innumerous key functions in all living cells and account for more than 30 percent of the eukaryotic proteomes. Two thirds of all known drugs on the market target membrane proteins, thus highlighting their critical importance in human health. While the unique structures of more than 15'000 soluble proteins are solved, the number of unique membrane protein structures is about 533 (April 2015). Clearly, there is an urgent need for structural information on membrane proteins in order to understand their function at the molecular level.
The research of the Fotiadis group focuses on the structure determination of integral membrane proteins and the elucidation of their supramolecular organization. To this end, target membrane proteins are cloned, overexpressed heterologously, purified and reconstituted into proteoliposomes and 2D crystals. Alternatively, membrane proteins are isolated directly from native tissues. Oligomeric state, projection map, 3D structure and surface topography are then determined from densely-packed proteoliposomes and 2D crystals by transmission electron microscopy, electron crystallography and atomic force microscopy. Using these approaches, the structures of membrane proteins can be determined in their native environment, the lipid bilayer.
Representative examples of structural works are the 3D structure of the plant aquaporin SoPIP2;1 (Kukulski et al., J. Mol. Biol. 2005), the supramolecular organization of the murine G protein-coupled receptor rhodopsin (Fotiadis et al., Nature 2003) and the projection structure of the amino acid transporter AdiC (Casagrande et al., J. Biol. Chem. 2008). In 2006 within the European genomics initiative on disorders of plasma membrane amino acid transporters (acronym: EUGINDAT) the Fotiadis group also started with the growth of 3D crystals of transport proteins for structure determination by X-ray crystallography.
To understand the molecular working mechanisms of membrane proteins, information on the structure and in particular on the function is indispensable. Therefore, we invested considerable amounts of time during the last years in establishing functional assays. One recent achievement was the successful establishment of the scintillation proximity assay for transport proteins in our laboratory (Harder and Fotiadis, Nature Protocols 2012).