Skip to main content
PMC home page
Biophysical Journal logoLink to Biophysical Journal
. 2000 Dec;79(6):3258–3266. doi: 10.1016/S0006-3495(00)76558-1

The mechanics of F-actin microenvironments depend on the chemistry of probing surfaces.

J L McGrath 1, J H Hartwig 1, S C Kuo 1
PMCID: PMC1301200  PMID: 11106629

Abstract

To understand the microscopic mechanical properties of actin networks, we monitor the motion of embedded particles with controlled surface properties. The highly resolved Brownian motions of these particles reveal the viscoelastic character of the microenvironments around them. In both non-cross-linked and highly cross-linked actin networks, particles that bind F-actin report viscoelastic moduli comparable to those determined by macroscopic rheology experiments. By contrast, particles modified to prevent actin binding have weak microenvironments that are surprisingly insensitive to the introduction of filament cross-links. Even when adjacent in the same cross-linked gel, actin-binding and nonbinding particles report viscoelastic moduli that differ by two orders of magnitude at low frequencies (0.5-1.5 rad/s) but converge at high frequencies (> 10(4) rad/s). For all particle chemistries, electron and light microscopies show no F-actin recruitment or depletion, so F-actin microheterogeneities cannot explain the deep penetration (approximately 100 nm) of nonbinding particles. Instead, we hypothesize that a local depletion of cross-linking around nonbinding particles explains the phenomena. With implications for organelle mobility in cells, our results show that actin binding is required for microenvironments to reflect macroscopic properties, and conversely, releasing actin enhances particle mobility beyond the effects of mere biochemical untethering.

Full Text

The Full Text of this article is available as a PDF (288.5 KB).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Brown S. S., Spudich J. A. Nucleation of polar actin filament assembly by a positively charged surface. J Cell Biol. 1979 Feb;80(2):499–504. doi: 10.1083/jcb.80.2.499. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Casella J. F., Barron-Casella E. A., Torres M. A. Quantitation of Cap Z in conventional actin preparations and methods for further purification of actin. Cell Motil Cytoskeleton. 1995;30(2):164–170. doi: 10.1002/cm.970300208. [DOI] [PubMed] [Google Scholar]
  3. Crocker J. C., Valentine M. T., Weeks E. R., Gisler T., Kaplan P. D., Yodh A. G., Weitz D. A. Two-point microrheology of inhomogeneous soft materials. Phys Rev Lett. 2000 Jul 24;85(4):888–891. doi: 10.1103/PhysRevLett.85.888. [DOI] [PubMed] [Google Scholar]
  4. Janmey P. A., Hvidt S., Lamb J., Stossel T. P. Resemblance of actin-binding protein/actin gels to covalently crosslinked networks. Nature. 1990 May 3;345(6270):89–92. doi: 10.1038/345089a0. [DOI] [PubMed] [Google Scholar]
  5. Ladd AJ, Gang H, Zhu JX, Weitz DA. Time-dependent collective diffusion of colloidal particles. Phys Rev Lett. 1995 Jan 9;74(2):318–321. doi: 10.1103/PhysRevLett.74.318. [DOI] [PubMed] [Google Scholar]
  6. Luby-Phelps K., Castle P. E., Taylor D. L., Lanni F. Hindered diffusion of inert tracer particles in the cytoplasm of mouse 3T3 cells. Proc Natl Acad Sci U S A. 1987 Jul;84(14):4910–4913. doi: 10.1073/pnas.84.14.4910. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Meechai N, Jamieson AM, Blackwell J. Translational Diffusion Coefficients of Bovine Serum Albumin in Aqueous Solution at High Ionic Strength. J Colloid Interface Sci. 1999 Oct 1;218(1):167–175. doi: 10.1006/jcis.1999.6401. [DOI] [PubMed] [Google Scholar]
  8. Nakata T., Hirokawa N. Organization of cortical cytoskeleton of cultured chromaffin cells and involvement in secretion as revealed by quick-freeze, deep-etching, and double-label immunoelectron microscopy. J Neurosci. 1992 Jun;12(6):2186–2197. doi: 10.1523/JNEUROSCI.12-06-02186.1992. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Palmer A., Xu J., Kuo S. C., Wirtz D. Diffusing wave spectroscopy microrheology of actin filament networks. Biophys J. 1999 Feb;76(2):1063–1071. doi: 10.1016/S0006-3495(99)77271-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Steyer J. A., Almers W. Tracking single secretory granules in live chromaffin cells by evanescent-field fluorescence microscopy. Biophys J. 1999 Apr;76(4):2262–2271. doi: 10.1016/S0006-3495(99)77382-0. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Tang J. X., Janmey P. A., Stossel T. P., Ito T. Thiol oxidation of actin produces dimers that enhance the elasticity of the F-actin network. Biophys J. 1999 Apr;76(4):2208–2215. doi: 10.1016/S0006-3495(99)77376-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Wachsstock D. H., Schwarz W. H., Pollard T. D. Cross-linker dynamics determine the mechanical properties of actin gels. Biophys J. 1994 Mar;66(3 Pt 1):801–809. doi: 10.1016/s0006-3495(94)80856-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Xu J., Schwarz W. H., Käs J. A., Stossel T. P., Janmey P. A., Pollard T. D. Mechanical properties of actin filament networks depend on preparation, polymerization conditions, and storage of actin monomers. Biophys J. 1998 May;74(5):2731–2740. doi: 10.1016/S0006-3495(98)77979-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Xu J., Wirtz D., Pollard T. D. Dynamic cross-linking by alpha-actinin determines the mechanical properties of actin filament networks. J Biol Chem. 1998 Apr 17;273(16):9570–9576. doi: 10.1074/jbc.273.16.9570. [DOI] [PubMed] [Google Scholar]
  15. Yamada S., Wirtz D., Kuo S. C. Mechanics of living cells measured by laser tracking microrheology. Biophys J. 2000 Apr;78(4):1736–1747. doi: 10.1016/S0006-3495(00)76725-7. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Biophysical Journal are provided here courtesy of The Biophysical Society

RESOURCES