title: Persistence length of fascin-cross-linked actin filament bundles in solution and the in vitro motility assay.
abstract: BACKGROUND
  Bundles of unipolar actin filaments (F-actin), cross-linked via the actin-binding protein fascin, are important in filopodia of motile cells and stereocilia of inner ear sensory cells. However, such bundles are also useful as shuttles in myosin-driven nanotechnological applications. Therefore, and for elucidating aspects of biological function, we investigate if the bundle tendency to follow straight paths (quantified by path persistence length) when propelled by myosin motors is directly determined by material properties quantified by persistence length of thermally fluctuating bundles.
  
  
  METHODS
  Fluorescent bundles, labeled with rhodamine-phalloidin, were studied at fascin:actin molar ratios: 0:1 (F-actin), 1:7, 1:4 and 1:2. Persistence lengths (Lp) were obtained by fitting the cosine correlation function (CCF) to a single exponential function: <cos(θ(0)-θ(s))>=exp(-s/(2Lp)) where θ(s) is tangent angle; s: path or contour lengths. < > denotes averaging over filaments.
  
  
  RESULTS
  Bundle-Lp (bundles<15μm long) increased from ~10 to 150μm with increased fascin:actin ratio. The increase was similar for path-Lp (path<15μm), with highly linear correlation. For longer bundle paths, the CCF-decay deviated from a single exponential, consistent with superimposition of the random path with a circular path as suggested by theoretical analysis.
  
  
  CONCLUSIONS
  Fascin-actin bundles have similar path-Lp and bundle-Lp, both increasing with fascin:actin ratio. Path-Lp is determined by the flexural rigidity of the bundle.
  
  
  CONCLUSIONS
  The findings give general insight into mechanics of cytoskeletal polymers that interact with molecular motors, aid rational development of nanotechnological applications and have implications for structure and in vivo functions of fascin-actin bundles.
authors.affiliation: Department of Chemistry and Biomedical Sciences, Linnaeus University, Kalmar SE-391 82, Sweden.
authors.forename: Hideyo
authors.initials: H
authors.lastname: Takatsuki
authors.affiliation: Department of Chemistry and Biomedical Sciences, Linnaeus University, Kalmar SE-391 82, Sweden.
authors.forename: Elina
authors.initials: E
authors.lastname: Bengtsson
authors.affiliation: Department of Chemistry and Biomedical Sciences, Linnaeus University, Kalmar SE-391 82, Sweden. Electronic address: alf.mansson@lnu.se.
authors.forename: Alf
authors.initials: A
authors.lastname: Månsson
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000502:physiology*; D002352:Carrier Proteins / Q000737:chemistry* / Q000502:physiology; D008840:Microfilament Proteins / Q000737:chemistry* / Q000502:physiology; D009068:Movement; D036103:Nanotechnology; D012996:Solutions
chemical_list: D002352:Carrier Proteins; D008840:Microfilament Proteins; D012996:Solutions; C020324:fascin
keywords: Actin; Fascin; Monte-Carlo simulation; Motility assay; Myosin; Persistence length