Date/Time
Date(s) - 30/01/2013
3:20 pm - 4:20 pm

Title: Diffusion of Transmembrane Proteins and Peptides Embedded in Lipid Bilayers

Speaker: Dr. Nicolas Taulier

Institute: Universite Pierre et Marie Curie

Location: ABB 102

Description:

Investigation of the structures, functions, and interactions of (trans)membrane proteins is still a challenge because of the difficulties related to their hydrophobic properties. When embedded in a membrane, (trans)membrane proteins move in a two dimensional space and their mobility can be evaluated through their diffusion coefficient (D). A hydrodynamic model developed by Saffman and Delbruck predicts that D exhibits a weak, logarithmic dependence with the protein radius R. Thus, for more than 30 years, it has been thought that information on the size of a diffusing object cannot be extracted from diffusion experiments. Despite its widespread use, the model validity has never been thoroughly investigated. We show that on the contrary diffusion coefficient strongly depends on the size of the diffusing object. We propose a heuristic model that leads to a Stokes-like expression (D proportional to 1/R). This new finding demonstrates that diffusion measurements may represent a fast and fruitful method to determine the oligomerization degree of proteins or studying lipid-protein and protein-protein interactions within bilayers. We specifically applied this idea to the study of the effect of hydrophobic mismatch on transmembrane peptides, where the diffusion coefficient can provide an estimate of the peptide tilt angle and of the membrane deformation caused by the membrane. We have also studied the interaction between two membrane proteins of an efflux pump of P. aeruginosa: MexA and OprM. From their diffusion we deduced their mode of interaction, the size, and the stoichiometry of the protein complex.