Dynamics of counterion-induced attraction between vimentin filaments followed in microfluidic drops.
Intermediate filaments (IFs) are fiber-forming proteins and part of the cytoskeleton of eukaryotes. In vitro the network formation of purified IF systems is mediated, for example, by the interaction with multivalent ions. The understanding of these interaction mechanisms increases the knowledge of the cytoskeleton on a fundamental level. Here, we employ time-lapse fluorescence microscopy to directly image the evolution of network formation of vimentin IFs upon addition of divalent ions. We are thus able to follow the process starting a few seconds after the first encounter of free filaments and ions up to several minutes when the networks are in equilibrium. The local protein density in the compacted networks can reach a factor of 45 higher than the original solution concentration. The competition between mono- and divalent ion condensation onto the protein explains our observations and reveals the polyelectrolyte nature of vimentin as a reason for the protein attraction in the presence of small cations. The method for time-lapse studies in microfluidic drops presented here can be generalized to other dynamic systems.
Institute for X-Ray Physics, Georg-August-Universität Göttingen, Germany and Center for Nanoscale Microscopy and Molecular Physiology of the Brain (CNMPB), Friedrich-Hund-Platz 1, 37077 Göttingen, Germany. sarah.koester@phys.uni-goettingen.de.
Christian
C
Dammann
Sarah
S
Köster
D019943:Amino Acid Substitution; D004129:Dimethylpolysiloxanes / Q000737:chemistry; D006801:Humans; D007382:Intermediate Filaments / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015636:Magnesium Chloride / Q000737:chemistry*; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation*; D008856:Microscopy, Fluorescence; D018715:Microscopy, Video; D008956:Models, Chemical; D055668:Photochemical Processes; D017319:Photosensitizing Agents / Q000737:chemistry / Q000528:radiation effects; D017354:Point Mutation; D011189:Potassium Chloride / Q000737:chemistry*; D066330:Printing, Three-Dimensional; D066329:Protein Aggregates; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013499:Surface Properties; D059008:Time-Lapse Imaging; D014466:Ultraviolet Rays; D014746:Vimentin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D004129:Dimethylpolysiloxanes; D017319:Photosensitizing Agents; D066329:Protein Aggregates; D011994:Recombinant Proteins; D014746:Vimentin; D015636:Magnesium Chloride; C013830:baysilon; D011189:Potassium Chloride