Divide-and-conquer crystallographic approach towards an atomic structure of intermediate filaments

Intermediate filaments (IFs) represent an essential component of the cytosk eleton in higher eukaryotic cells. The elementary building block of the IF architecture is an elongated dimer with its dominant central part being a p arallel double-stranded a-helical coiled coil. Filament formation proceeds via a specific multi-step association of the dimers into the unit-length fi laments, which subsequently anneal longitudinally and finally radially comp act into mature filaments. To tackle the challenge of a crystallographic st ructure determination, we have produced and characterised 17 overlapping so luble fragments of human IF protein vimentin. For six fragments ranging in length between 39 and 84 amino acid residues, conditions yielding macroscop ic crystals could be established and X-ray diffraction data were collected to the highest resolution limit between 1.4 and 3 Angstrom. We expect that solving the crystal structures of these and further fragments will eventual ly allow us to patch together a molecular model for the full-length vimenti n dimer. This divide-and-conquer approach will be subsequently extended to determining the crystal structures of a number of complexes formed by appro priate vimentin fragments, and will eventually allow us to establish the th ree-dimensional architecture of complete filaments at atomic resolution. (C ) 2001 Academic Press.