title: Impact of ion valency on the assembly of vimentin studied by quantitative small angle X-ray scattering.
abstract: The assembly kinetics of intermediate filament (IF) proteins from tetrameric complexes to single filaments and networks depends on the protein concentration, temperature and the ionic composition of their environment. We systematically investigate how changes in the concentration of monovalent potassium and divalent magnesium ions affect the internal organization of the resulting filaments. Small angle X-ray scattering (SAXS) is very sensitive to changes in the filament cross-section such as diameter or compactness. Our measurements reveal that filaments formed in the presence of magnesium chloride differ distinctly from filaments formed in the presence of potassium chloride. The principle multi-step assembly mechanism from tetramers via unit-length filaments (ULF) to elongated filaments is not changed by the valency of ions. However, the observed differences indicate that the magnesium ions free the head domains of tetramers from unproductive interactions to allow assembly but at the same time mediate strong inter-tetrameric interactions that impede longitudinal annealing of unit-length filaments considerably, thus slowing down filament growth.
authors.forename: Martha E
authors.initials: ME
authors.lastname: Brennich
authors.forename: Susanne
authors.initials: S
authors.lastname: Bauch
authors.forename: Ulla
authors.initials: U
authors.lastname: Vainio
authors.forename: Tatjana
authors.initials: T
authors.lastname: Wedig
authors.forename: Harald
authors.initials: H
authors.lastname: Herrmann
authors.forename: Sarah
authors.initials: S
authors.lastname: Köster
mesh_terms: D003599:Cytoskeleton / Q000737:chemistry / Q000648:ultrastructure; D007381:Intermediate Filament Proteins / Q000737:chemistry* / Q000648:ultrastructure; D007382:Intermediate Filaments / Q000737:chemistry / Q000648:ultrastructure*; D007477:Ions / Q000737:chemistry; D007700:Kinetics; D053838:Scattering, Small Angle; D014746:Vimentin / Q000737:chemistry* / Q000648:ultrastructure; D014961:X-Ray Diffraction
chemical_list: D007381:Intermediate Filament Proteins; D007477:Ions; D014746:Vimentin