Thomas, Clément , Hoffmann, Céline , Dieterle, M , Moreau, Flora , Gatti, Sabrina , Papuga, Jessica , Tholl, Stephane , Steinmetz, André .
Actin filament bundling via LIM domains.
The actin cytoskeleton plays an essential role in cellular trafficking in that it serves as tracks for the transport of a variety of small cellular structures such as Golgi-derived cargo vesicles and small organelles. To properly carry out this task, actin filaments, which are a chain of juxtaposed actin units held together by physical forces, need to be stabilized and protected from destabilizing activities by associating with proteins able to bind distant actin units in a filament. Such a stabilization effect can be enhanced by assembling several filaments into higher order structures such as actin cables. The formation of actin cables (actin filament bundling) is controlled by a number of proteins which include fimbrins, villins and formins. Our recent results suggest that the plant LIM proteins are also members of the actin bundling protein family (Thomas et al., 2006; Plant Cell 18: 2194-2206). Flowering plants express up to 6 LIM genes which can be classified according to their amino acid sequence and expression pattern. We have used in vivo and in vitro assays to study the role of a tobacco LIM protein (WLIM1) in F-actin structure and dynamics. Using a GFP-tagged version of WLIM1 we observed that this protein accumulates along and stabilizes actin filaments in tobacco BY2 and leaf epidermal cells. Importantly, overexpression of the fusion protein induced the formation of very thick actin cables. High- and low-speed centrifugations revealed that WLIM1 has the ability to bind actin filaments directly and with a high affinity and to trigger efficient actin bundling. A domain analysis allowed us to identify the LIM domains as the peptide motifs responsible for the F-actin binding, stabilizing and bundling activities of WLIM1. Interestingly, each individual LIM domain was found able to trigger these three activities in an autonomous manner, although with a reduced efficiency compared to the native WLIM1 protein. In conclusion, the LIM domains define new class of actin binding and bundling modules. They cooperate in WLIM1 to confer this protein high actin binding and bundling activities.
Log in to add this item to your schedule
1 - Centre de Recherche Public-Santé, Plant Molecular Biology, 84, Val Fleuri, Luxembourg, L-1526, Luxembourg
Presentation Type: ASPB Minisymposium
Location: Continental B/Hilton
Date: Wednesday, July 11th, 2007
Time: 10:40 AM