title: Measuring cohesion between macromolecular filaments one pair at a time: depletion-induced microtubule bundling.
abstract: In the presence of nonadsorbing polymers, colloidal particles experience ubiquitous attractive interactions induced by depletion forces. Here, we measure the depletion interaction between a pair of microtubule filaments using a method that combines single filament imaging with optical trapping. By quantifying the dependence of filament cohesion on both polymer concentration and solution ionic strength, we demonstrate that the minimal model of depletion, based on the Asakura-Oosawa theory, fails to quantitatively describe the experimental data. By measuring the cohesion strength in two- and three- filament bundles, we verify pairwise additivity of depletion interactions for the specific experimental conditions. The described experimental technique can be used to measure pairwise interactions between various biological or synthetic filaments and complements information extracted from bulk osmotic stress experiments.
authors.affiliation: Department of Physics, Brandeis University, Waltham, Massachusetts 02454, USA.
authors.forename: Feodor
authors.initials: F
authors.lastname: Hilitski
authors.affiliation: Department of Physics, Brandeis University, Waltham, Massachusetts 02454, USA.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Ward
authors.affiliation: Department of Physics, University of Massachusetts at Amherst, Amherst, Massachusetts 01003, USA.
authors.forename: Luis
authors.initials: L
authors.lastname: Cajamarca
authors.affiliation: Department of Physics, Brandeis University, Waltham, Massachusetts 02454, USA.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Hagan
authors.affiliation: Department of Polymer Science and Engineering, University of Massachusetts at Amherst, Amherst, Massachusetts 01003, USA.
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Grason
authors.affiliation: Department of Physics, Brandeis University, Waltham, Massachusetts 02454, USA.
authors.forename: Zvonimir
authors.initials: Z
authors.lastname: Dogic
mesh_terms: D003599:Cytoskeleton / Q000737:chemistry* / Q000378:metabolism*; D003911:Dextrans / Q000737:chemistry; D019277:Entropy; D008870:Microtubules / Q000737:chemistry* / Q000378:metabolism*; D008954:Models, Biological; D011092:Polyethylene Glycols / Q000737:chemistry
chemical_list: D003911:Dextrans; D011092:Polyethylene Glycols