Membrane proteins are involved in major cellular processes e.g. cell homeostasis, bioenergetics, cell division and communication. Nearly 25% of genes encode for a membrane protein and these include protein targets for over about 50 % of all drugs in use today.
Their knowledge at the molecular level that is needed for the conception of new pharmacological tools lacks far beyond those of the cytoplasmic proteins. This is due to their amphiphilic character that complicates their handling from the overexpression, the purification to the structural analysis. Our team combines membrane biochemistry, physico-chemistry and cell biology to tackle specific biological questions involving transmembrane or membrane bound proteins. Our specificity is to develop new biomimetic membrane systems that are further used for the analysis of membrane proteins in a native like-environment (1,2). Our favorite tool is cryo-electron microscopy and cryo-tomography for building 3D models of proteins in their membrane environment. The membrane proteins under studies are involved in cellular multidrug resistance and detoxification and in cell division and multicellularisation.
Our most significant projects and findings over the past few years include:
New methods of reconstitution of membrane proteins in lipidic membrane
Following the pioneered work of the team of J.L.Rigaud on the reconstitution of membrane proteins in liposomes (A), we developed new membrane systems with transmembrane and/or membrane associated proteins for functional or structural studies: – reconstitution of membrane proteins in Giant Unilamellar Vesicles (C); 2D crystallization by the lipid layer; Reconstitution in planar lipid bilayer for AFM analysis (B). The main interest of these last two methods is to decrease to the picomole level the amount of proteins needed for the structural analysis and thus to get access to human membrane proteins that are poorly expressed.
Multidrugs Resistant transporters
ABC (ATP-binding cassette) transporters are membrane transporters that hydrolyse ATP for the transmembrane transport of various xenobiotics and the cell detoxification. Several ABC’s confers a multidrug resistance phenotype (MDR) to bacteria against antibiotics and to human against drugs use in anticancer treatments. Our project includes the structural analysis of bacterial homolog and human MDR transporters involved in the transport of anticancer drugs with the final aim to contribute to the conception of new inhibitors. We recently described the molecular architecture of ABCG2 (Breast Cancer Resistance Protein), a human ABC transporter, of BmrA and of BmrC/BmrD, MDR transporters homologs to the human Pgp and MRP1, respectively .
Septins are cytoskeletal filamentous proteins which are bound to the inner cell membrane and are involved in membrane remodeling processes (constriction, invagination). Septins are multi-tasking proteins and have a prominent role in cell division, neuron morphogenesis, bacterial invasion, cell motility, membrane rigidity. This “so called” fourth cytoskeletal member can make scaffolds to recruit other factors and is implicated in establishing diffusion barriers between cellular compartments. Septins interact specifically with phosphoinositides. As opposed to other cytoskeletal proteins (actin, tubulin) septins polymerize in a non-polar fashion into paired filaments. Septins further self-assemble into variable organizations (rods, filaments, rings, gauzes) both in vitro and in situ (1-3), most likely depending on the proteic content and the post-translational modification state within the septin complexes.
We focus our interest in understanding how septins from distinct organisms interact with specific partners: membrane and proteins (cytoskeletal proteins (actin) and transmembrane proteins). To this end we are using a set of complementary microscopy methods (cryo-electron microscopy, fluorescence microcopy and atomic force microscopy).
- Bertin et al. (2012), Molecular Biology of the Cell, 23(3), 423-432.
- Bertin et al. (2010), J. Mol. Biol., 404(4), 711-31.
A.Bertin et al. (2008), Proc.Natl. Acac. Sci USA, 105, 8274-8279
Cryo-electron microscopy and cryo tomography of biomimetic systems/PICT IBISA
Within the PICT-IBISA of Cell imaging and in collaboration, we also analyse different biomimetic systems by cryo-electron microscopy (see Publications).