title: Effects of basic calponin on the flexural mechanics and stability of F-actin.
abstract: The cellular actin cytoskeleton plays a central role in the ability of cells to properly sense, propagate, and respond to external stresses and other mechanical stimuli. Calponin, an actin-binding protein found both in muscle and non-muscle cells, has been implicated in actin cytoskeletal organization and regulation. In this work, we studied the mechanical and structural interaction of actin with basic calponin, a differentiation marker in smooth muscle cells, on a single filament level. We imaged fluorescently labeled thermally fluctuating actin filaments and found that at moderate calponin binding densities, actin filaments were more flexible, evident as a reduction in persistence length from 8.0 to 5.8 μm. When calponin-decorated actin filaments were subjected to shear, we observed a marked reduction of filament lengths after decoration with calponin, which we argue was due to shear-induced filament rupture rather than depolymerization. This increased shear susceptibility was exacerbated with calponin concentration. Cryo-electron microscopy results confirmed previously published negative stain electron microscopy results and suggested alterations in actin involving actin subdomain 2. A weakening of F-actin intermolecular association is discussed as the underlying cause of the observed mechanical perturbations.
authors.affiliation: Department of Physiology and Biophysics, Boston University, Boston, Massachusetts, USA.
authors.forename: Mikkel Herholdt
authors.initials: MH
authors.lastname: Jensen
authors.forename: James
authors.initials: J
authors.lastname: Watt
authors.forename: Julie L
authors.initials: JL
authors.lastname: Hodgkinson
authors.forename: Cynthia
authors.initials: C
authors.lastname: Gallant
authors.forename: Sarah
authors.initials: S
authors.lastname: Appel
authors.forename: Mohammed
authors.initials: M
authors.lastname: El-Mezgueldi
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Angelini
authors.forename: Kathleen G
authors.initials: KG
authors.lastname: Morgan
authors.forename: William
authors.initials: W
authors.lastname: Lehman
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Moore
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000199:Actins / Q000032:analysis / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D020285:Cryoelectron Microscopy; D003599:Cytoskeleton / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008840:Microfilament Proteins / Q000378:metabolism*; D008854:Microscopy, Electron; D011485:Protein Binding; D000096985:Calponins
chemical_list: D000199:Actins; D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D000096985:Calponins