Séminaire Rut Carballido-Lopez

Assembly of bacterial actin MreB on lipid surfaces

One of the ultimate goals in cell biology is to understand how cells determine their shape. In bacteria, the cell wall and actin-like MreB proteins are major determinants of cell shape. Using cutting-edge fluorescence microscopy techniques combined with automated single particle and single molecule tracking in live cells of the model Gram-positive bacterium Bacillus subtilis, we showed that MreB proteins form membrane-associated nanofilaments that move circumferentially along the sidewalls together with cell wall synthetic enzymes. These findings led to the current model, in which MreB spatiotemporally patterns cell wall insertion, promoting cylindrical elongation. In parallel, to fill in the gap between structure and cellular function, we investigate the biochemical and polymerization properties of B. subtilis MreB in vitro.  We have shown that both lipids and ATP/GTP are facilitators of MreB polymerization into straight pairs of filaments, with a dual effect of nucleotide, in promoting both membrane binding and filaments assembly/disassembly. We have also implemented methods for observation of MreB polymerization and filament dynamics on biomimetic membrane systems. Using TIRFM-based single filament imaging and High-speed atomic force microscopy (HS-AFM) , we have revealed important insights into the properties of MreB filaments and their interaction with lipid surfaces. The combination of our top-down and bottom-up approaches to investigate MreB promises exciting advances in the near future.