Conserved segments 1A and 2B of the intermediate filament dimer: their atomic structures and role in filament assembly

Abstract

Intermediate ®laments (IFs) are key components of the cytoskeleton in higher eukaryotic cells. The elementary IF`building block' is an elongated coiled-coil dimer consisting of four consecutive a-helical segments. The segments 1A and 2B include highly conserved sequences and are critically involved in IF assembly. Based on the crystal structures of three human vimentin fragments at 1.4±2.3 A Ê resolution (PDB entries 1gk4, 1gk6 and 1gk7), we have established the molecular organization of these two segments. The fragment corresponding to segment 1A forms a single, amphipatic a-helix, which is compatible with a coiled-coil geometry. While this segment might yield a coiled coil within an isolated dimer, monomeric 1A helices are likely to play a role in speci®c dimer±dimer interactions during IF assembly. The 2B segment reveals a double-stranded coiled coil, which unwinds near residue Phe351 to accommodate a`stutter'. A fragment containing the last seven heptads of 2B interferes heavily with IF assembly and also transforms mature vimentin ®laments into a new kind of structure. These results provide the ®rst insight into the architecture and functioning of IFs at the atomic level.

Intermediate Filament Diseases: Desminopathy

“…30 The "stutter" is an obligatory feature of all IF proteins and its position is absolutely conserved. 31 Experimental "straightening out" of the stutter by inserting three "missing" amino acids to restore a continuous heptad repeat leads to inability of this "stutterless" molecule to anneal into longer filaments. 32 As a compensation for the stutter, the coiled coil slightly unwinds in the stutter vicinity.…”

Structures of the lamin A/C R335W and E347K mutants: Implications for dilated cardiolaminopathies

“…The side chains of Arg335 and Glu347, mutated in this work, are shown by the crystal structures to be exposed at the surface of the coiled coil dimer (Fig. 3); nevertheless, the mutations occur at sites that are highly conserved in the known LMNA amino acid sequences [11,39]. Within the vertebrate IF superfamily, Arg335 is a highly conserved residue, stressing its key role in the correctly folded coil/rod.…”

Identification of calpain cleavage sites in the G1 cyclin-dependent kinase inhibitor p19INK4d

“…A typical example is provided by the m-calpain proteolysis of vimentin. Vimentin belongs to the intermediate filament (IF) family of proteins (Strelkov et al, 2002). All IF proteins share a common structural organization of the dimer that includes a central coiledcoil 'rod' domain flanked by 'head' and 'tail' domains at both ends (Fuchs and Weber, 1994;Strelkov et al, 2002).…”

“…Vimentin belongs to the intermediate filament (IF) family of proteins (Strelkov et al, 2002). All IF proteins share a common structural organization of the dimer that includes a central coiledcoil 'rod' domain flanked by 'head' and 'tail' domains at both ends (Fuchs and Weber, 1994;Strelkov et al, 2002). The a-helical core part is not continuous, however, but interrupted in several places, resulting in four consecutive a-helical segments that are connected by linkers.…”