The LIM domains of WLIM1 define a new class of actin bundling modules.
Actin filament bundling, i.e. the formation of actin cables, is an important process that relies on proteins able to directly bind and cross-link subunits of adjacent actin filaments. Animal cysteine-rich proteins and their plant counterparts are two LIM domain-containing proteins that were recently suggested to define a new family of actin cytoskeleton regulators involved in actin filament bundling. We here identified the LIM domains as responsible for F-actin binding and bundling activities of the tobacco WLIM1. The deletion of one of the two LIM domains reduced significantly, but did not entirely abolish, the ability of WLIM1 to bind actin filaments. Individual LIM domains were found to interact directly with actin filaments, although with a reduced affinity compared with the native protein. Variants lacking the C-terminal or the inter-LIM domain were only weakly affected in their F-actin stabilizing and bundling activities and trigger the formation of thick cables containing tightly packed actin filaments as does the native protein. In contrast, the deletion of one of the two LIM domains negatively impacted both activities and resulted in the formation of thinner and wavier cables. In conclusion, we demonstrate that the LIM domains of WLIM1 are new autonomous actin binding and bundling modules that cooperate to confer WLIM1 high actin binding and bundling activities.
Thomas
Clément
C
Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg. Electronic address: clement.thomas@crp-sante.lu.
Moreau
Flora
F
Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg.
Dieterle
Monika
M
Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg.
Hoffmann
Céline
C
Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg.
Gatti
Sabrina
S
Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg.
Hofmann
Christina
C
Institut de Biologie Moléculaire des Plantes, Centre National de la Recherche Scientifique, F-67084 Strasbourg, France.
Van Troys
Marleen
M
VIB Department of Medical Protein Research, Ugent and Department of Biochemistry, Faculty of Medicine and Health Sciences, B-9052 Ghent, Belgium.
Ampe
Christophe
C
VIB Department of Medical Protein Research, Ugent and Department of Biochemistry, Faculty of Medicine and Health Sciences, B-9052 Ghent, Belgium.
Steinmetz
André
A
Centre de Recherche Public-Santé, Luxembourg, L-1526 Luxembourg.
D008841:Actin Cytoskeleton / Q000737:chemistry*; D000199:Actins / Q000737:chemistry*; D001665:Binding Sites; D003599:Cytoskeleton / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000737:chemistry / Q000378:metabolism; D018398:Homeodomain Proteins / Q000737:chemistry / Q000502:physiology*; D007700:Kinetics; D008840:Microfilament Proteins / Q000737:chemistry; D018613:Microscopy, Confocal / Q000379:methods; D010940:Plant Proteins / Q000737:chemistry / Q000502:physiology*; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D014026:Nicotiana / Q000378:metabolism