title: Diffusion of GPI-anchored proteins is influenced by the activity of dynamic cortical actin.
abstract: Molecular diffusion at the surface of living cells is believed to be predominantly driven by thermal kicks. However, there is growing evidence that certain cell surface molecules are driven by the fluctuating dynamics of cortical cytoskeleton. Using fluorescence correlation spectroscopy, we measure the diffusion coefficient of a variety of cell surface molecules over a temperature range of 24-37 °C. Exogenously incorporated fluorescent lipids with short acyl chains exhibit the expected increase of diffusion coefficient over this temperature range. In contrast, we find that GPI-anchored proteins exhibit temperature-independent diffusion over this range and revert to temperature-dependent diffusion on cell membrane blebs, in cells depleted of cholesterol, and upon acute perturbation of actin dynamics and myosin activity. A model transmembrane protein with a cytosolic actin-binding domain also exhibits the temperature-independent behavior, directly implicating the role of cortical actin. We show that diffusion of GPI-anchored proteins also becomes temperature dependent when the filamentous dynamic actin nucleator formin is inhibited. However, changes in cortical actin mesh size or perturbation of branched actin nucleator Arp2/3 do not affect this behavior. Thus cell surface diffusion of GPI-anchored proteins and transmembrane proteins that associate with actin is driven by active fluctuations of dynamic cortical actin filaments in addition to thermal fluctuations, consistent with expectations from an "active actin-membrane composite" cell surface.
authors.affiliation: National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560065, India.
authors.forename: Suvrajit
authors.initials: S
authors.lastname: Saha
authors.affiliation: Department of Chemistry, Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720.
authors.forename: Il-Hyung
authors.initials: IH
authors.lastname: Lee
authors.affiliation: Raman Research Institute, Bangalore 560080, India.
authors.forename: Anirban
authors.initials: A
authors.lastname: Polley
authors.affiliation: Department of Chemistry, Howard Hughes Medical Institute, University of California, Berkeley, Berkeley, CA 94720.
authors.forename: Jay T
authors.initials: JT
authors.lastname: Groves
authors.affiliation: National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560065, India Raman Research Institute, Bangalore 560080, India madan@rri.res.in mayor@ncbs.res.in.
authors.forename: Madan
authors.initials: M
authors.lastname: Rao
authors.affiliation: National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore 560065, India Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India madan@rri.res.in mayor@ncbs.res.in.
authors.forename: Satyajit
authors.initials: S
authors.lastname: Mayor
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D003412:Cricetulus; D003599:Cytoskeleton / Q000378:metabolism; D004058:Diffusion; D005456:Fluorescent Dyes / Q000737:chemistry; D017261:Glycosylphosphatidylinositols / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D013050:Spectrometry, Fluorescence
chemical_list: D000199:Actins; D005456:Fluorescent Dyes; D017261:Glycosylphosphatidylinositols; D008565:Membrane Proteins; D002784:Cholesterol