Solubility properties and specific assembly pathways of the B-type lamin from Caenorhabditis elegans.
Lamins are nucleus-specific intermediate filament (IF) proteins that together with a complex set of membrane proteins form a filamentous meshwork tightly adhering to the inner nuclear membrane and being associated with the nuclear pore complexes. This so-called nuclear lamina provides mechanical stability and, in addition, has been implicated in the spatial organization of the heterochromatin. While increasing knowledge on the biological function of lamins has been obtained in recent years, the assembly mechanism of lamin filaments at the molecular level has remained largely elusive. Therefore, we have now more systematically investigated lamin assembly in vitro. Using Caenorhabditis elegans lamin, which has been reported to assemble into 10-nm filaments under low ionic strength conditions, we investigated the assembly kinetics of this protein into filaments in more detail using both His-tagged and un-tagged recombinant proteins. In particular, we have characterized distinct intermediates in the filament assembly process by analytical ultracentrifugation, electron and atomic force microscopy. In contrast to the general view that lamins assemble only slowly into filaments, we show that in vitro association reactions are extremely fast, and depending on the ionic conditions employed, significant filamentous assemblies form within seconds.
Foeger
Nicole
N
Division of Molecular Genetics, German Cancer Research Center, Im Neuenheimer Feld 580, D-69120 Heidelberg, Germany.
Wiesel
Naama
N
Lotsch
Dorothee
D
Mücke
Norbert
N
Kreplak
Laurent
L
Aebi
Ueli
U
Gruenbaum
Yosef
Y
Herrmann
Harald
H
D000818:Animals; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D002467:Cell Nucleus / Q000378:metabolism; D019281:Dimerization; D007381:Intermediate Filament Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D034882:Lamins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D018625:Microscopy, Atomic Force / Q000379:methods; D046529:Microscopy, Electron, Transmission / Q000379:methods; D012995:Solubility
D029742:Caenorhabditis elegans Proteins; D007381:Intermediate Filament Proteins; D034882:Lamins