Biophysical Journal 70: 609-625 (1996)
© 1996 the Biophysical Society

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Käs, J Articles by Janmey, P A Search for Related Content PubMed PubMed Citation Articles by Käs, J Articles by Janmey, P A

F-actin, a model polymer for semiflexible chains in dilute, semidilute, and liquid crystalline solutions.

Division of Experimental Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA. kas@calvin.bwh.harvard.edu

ABSTRACT

Single actin filaments were analyzed in solutions ranging from dilute (0.2 microgram/ml), where filaments interact only with solvent, to concentrations (4.0 mg/ml) at which F-actin forms a nematic phase. A persistence length of approximately 1.8 microns and an average length of approximately 22 microns (Kaufmann et al., 1992) identify actin as a model for studying the dynamics of semiflexible polymers. In dilute solutions the filaments exhibit thermal bending undulations in addition to diffusive motion. At higher semidilute concentrations (1.4 mg/ml) three-dimensional reconstructions of confocal images of fluorescently labeled filaments in a matrix of unlabeled F-actin reveal steric interactions between filaments, which account for the viscoelastic behavior of these solutions. The restricted undulations of these labeled chains reveal the virtual tube formed around a filament by the surrounding actin. The average tube diameter <a> scales with monomer concentration c as <a> varies; is directly proportional to c-(0.5 +/- 0.15). The diffusion of filaments in semidilute solutions (c = (0.1-2.0) mg/ml) is dominated by diffusion along the filament contour (reptation), and constraint release by remodeling of the surrounding filaments is rare. The self-diffusion coefficient D parallel along the tube decreases linearly with the chain length for semidilute solutions. For concentrations > 2.5 mg/ml a transition occurs from an isotropic entangled phase to a coexistence between isotropic and nematic domains. Analysis of the molecular motions of filaments suggests that the filaments in the aligned domains are in thermal equilibrium and that the diffusion coefficient parallel to the director D parallel is nearly independent of filament length. We also report the novel direct observation of u-shaped defects, called hairpins, in the nematic domains.

This article has been cited by other articles:

				M. Tassieri, R. M. L. Evans, L. Barbu-Tudoran, J. Trinick, and T. A. Waigh The Self-Assembly, Elasticity, and Dynamics of Cardiac Thin Filaments Biophys. J., March 15, 2008; 94(6): 2170 - 2178. [Abstract] [Full Text] [PDF]

				Q. Zhu, C. Vera, R. J. Asaro, P. Sche, and L. A. Sung A Hybrid Model for Erythrocyte Membrane: A Single Unit of Protein Network Coupled with Lipid Bilayer Biophys. J., July 15, 2007; 93(2): 386 - 400. [Abstract] [Full Text] [PDF]

				C. P. Brangwynne, G. H. Koenderink, E. Barry, Z. Dogic, F. C. MacKintosh, and D. A. Weitz Bending Dynamics of Fluctuating Biopolymers Probed by Automated High-Resolution Filament Tracking Biophys. J., July 1, 2007; 93(1): 346 - 359. [Abstract] [Full Text] [PDF]

				E. Helfer, P. Panine, M.-F. Carlier, and P. Davidson The Interplay between Viscoelastic and Thermodynamic Properties Determines the Birefringence of F-Actin Gels Biophys. J., July 1, 2005; 89(1): 543 - 553. [Abstract] [Full Text] [PDF]

				O. I. Wagner, J. Lifshitz, P. A. Janmey, M. Linden, T. K. McIntosh, and J.-F. Leterrier Mechanisms of Mitochondria-Neurofilament Interactions J. Neurosci., October 8, 2003; 23(27): 9046 - 9058. [Abstract] [Full Text] [PDF]

				X. Liu and G. H. Pollack Mechanics of F-Actin Characterized with Microfabricated Cantilevers Biophys. J., November 1, 2002; 83(5): 2705 - 2715. [Abstract] [Full Text] [PDF]

				M. A. Dichtl and E. Sackmann Microrheometry of semiflexible actin networks through enforced single-filament reptation: Frictional coupling and heterogeneities in entangled networks PNAS, May 1, 2002; (2002) 52432499. [Abstract] [Full Text] [PDF]

				G. N. Maksym, B. Fabry, J. P. Butler, D. Navajas, D. J. Tschumperlin, J. D. Laporte, and J. J. Fredberg Mechanical properties of cultured human airway smooth muscle cells from 0.05 to 0.4 Hz J Appl Physiol, October 1, 2000; 89(4): 1619 - 1632. [Abstract] [Full Text] [PDF]