title: The mechanical properties of hydrated intermediate filaments: insights from hagfish slime threads.
abstract: Intermediate filaments (IFs) impart mechanical integrity to cells, yet IF mechanics are poorly understood. It is assumed that IFs in cells are as stiff as hard alpha-keratin, F-actin, and microtubules, but the high bending flexibility of IFs and the low stiffness of soft alpha-keratins suggest that hydrated IFs may be quite soft. To test this hypothesis, we measured the tensile mechanics of the keratin-like threads from hagfish slime, which are an ideal model for exploring the mechanics of IF bundles and IFs because they consist of tightly packed and aligned IFs. Tensile tests suggest that hydrated IF bundles possess low initial stiffness (E(i) = 6.4 MPa) and remarkable elasticity (up to strains of 0.34), which we attribute to soft elastomeric IF protein terminal domains in series with stiffer coiled coils. The high tensile strength (180 MPa) and toughness (130 MJ/m(3)) of IF bundles support the notion that IFs lend mechanical integrity to cells. Their long-range elasticity suggests that IFs may also allow cells to recover from large deformations. X-ray diffraction and congo-red staining indicate that post-yield deformation leads to an irreversible alpha-->beta conformational transition in IFs, which leads to plastic deformation, and may be used by cells as a mechanosensory cue.
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada. dfudge@interchange.ubc.edu
authors.forename: Douglas S
authors.initials: DS
authors.lastname: Fudge
authors.forename: Kenn H
authors.initials: KH
authors.lastname: Gardner
authors.forename: V Trevor
authors.initials: VT
authors.lastname: Forsyth
authors.forename: Christian
authors.initials: C
authors.lastname: Riekel
authors.forename: John M
authors.initials: JM
authors.lastname: Gosline
mesh_terms: D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D004396:Coloring Agents / Q000494:pharmacology; D003224:Congo Red / Q000494:pharmacology; D019277:Entropy; D006196:Hagfishes / Q000502:physiology*; D007382:Intermediate Filaments / Q000737:chemistry* / Q000502:physiology; D007633:Keratins / Q000737:chemistry; D015233:Models, Statistical; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012623:Seawater; D013718:Tensile Strength; D013816:Thermodynamics; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D004396:Coloring Agents; D014867:Water; D003224:Congo Red; D007633:Keratins