A crystal structure of coil 1B of vimentin in the filamentous form provides a model of a high-order assembly of a vimentin filament

Vimentin is an intermediate filament (IF) protein that is expressed in leukocytes, fibroblasts and endothelial cells of blood vessels. Vimentin filaments contribute to structural stability of the cell membrane, organelle positioning and protein transport. Vimentin self-assembles into a dimer that subsequently forms high-order structures, including tetramers and octamers. The details of IF assembly at crystallographic resolutions are limited to the tetrameric form. We describe a crystal structure of a fragment of a vimentin rod domain (coil 1B) with a dimer of tetramers in the asymmetric unit. Coil 1B in the crystal is in an infinitely high-order filamentous assembly state, in which the tetramers are packed against each other laterally in an antiparallel fashion across the crystal lattice. In one of the directions of lateral packing, the tetramers pack against each other strictly head-to-tail, and in the orthogonal direction the tetramers pack in a staggered manner. This organization of the tetramers of coil 1B in the crystal lattice, together with previously reported biochemical and structural data, yield a model of high-order vimentin filament assembly. Database: Structural data are available in the PDB under the accession number 5WHF.