Measuring diffusion coefficients is a basic experimental approach of widespread use to decipher membrane organisation and dynamic processes. However, some fundamental aspects of diffusion still lack an explicative understanding in the absence of which misleading conclusions can be drawn.
- Diffusion of lipids and proteins influenced by the shape fluctuations of the membrane (E. Haanappel, L. Salomé)
- Nanohydrodynamics of Single Particle Tracking experiments (E. Haanappel)
Protein-induced membrane confinement
Membrane microdomains, often referred to as rafts, have been correlated to signalling and to intra-cellular transport phenomena. On the basis of original hypotheses (Joly, 2004; Destainville, Dumas & Salomé, 2008), we explore what physical principles are behind the existence of membrane microdomains. In the context of both hypotheses, proteins are perceived as playing a central role in the assembly and maintenance of membrane microdomains.
- Domains nucleated around lipids in ordered phase (E. Joly)
- Confinement induced by lipid-mediated inter-protein interactions (F. Dumas, L. Salomé)
Receptors diffusion, compartmentalization and signalling
- Role of cytoskeleton and associated proteins on MOP receptor compartmentalization (C. Tardin – collaboration with C. Lutz, IPBS) The Mu opioid (MOP) receptor is a G-protein coupled receptor whose activation contributes to attenuate pain sensation. In addition to the mechanism mentioned above, the filaments of the cytoskeleton or the associated proteins may contribute to the compartmentalization of MOP receptors (Lopez and Salomé, 2009).
- Cross-talk between NPFF and MOP receptors (Mazères S, Tardin C, Haanappel E., Lopez A., L. Salomé in collaboration with L. Mouledous, C. Mollereau, J.M. Zajac, IPBS) In collaboration with the group of J.M. Zajac (IPBS), we demonstrated that the stimulation of the neuropeptide NPFF receptor which changes MOP signalling also drastically modifies its diffusional behaviour in the plasma membrane (Roumy et al, 2007). We intend now to understand this phenomenon by a thorough experimental study by vrFRAP and SPT of the reciprocity and specificity of the cross-talk between these receptors.
- Dynamic organization of CD4 and CCR5, HIV co-receptors (P. Preira, F. Dumas, L. Salomé) CD4 and CCR5 are two receptors involved in the entry of human immunodeficiency virus after successive interactions with the viral envelope glycoprotein gp120. We demonstrated, in collaboration with F Bachelerie (Pasteur Institute, Paris), the constitutive association of CD4 and CCR5 by FRET experiments (Gaibelet et al, 2006). By vrFRAP experiments, we found that (i) these receptors expressed alone are confined into micrometer-sized domains (ii) CD4-CCR5 associations occur in smaller domains (iii) these interactions involve multiple CCR5 molecules per CD4 (Baker et al, 2007). These first studies had been realized with tagged receptors expressed in HEK cells and further investigations by SPT are pursued on cells competent for the infection.
Membrane fluidity and function
Formation of nuclear envelope (F. Dumas in collaboration with. B. Larijani, Cancer Research Institute, London)