Polymerization of G-actin by hydrodynamic shear stresses

J. Borejdo, A. Muhlrad, S. J. Leibovich, A. Oplatka

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In the absence of Ca2+ G-actin can be polymerized by the application of shear stress in low ionic strength buffer. When G-actin in low ionic strength buffer containing EGTA was sheared for predetermined times under different velocity gradients, viscosity attained a maximal value, comparable to that obtained by seeding with F-actin nuclei, at a velocity gradient of 3000 s-1 after about one hour. Such fiow-polymerized actin was indistinguishable from KCl-polymerized actin. Under similar conditions, EDTA which can bind both Ca2+ and Mg2+, gave a smaller effect than the Ca2+-chelating agent EGTA which binds Mg2+ weakly. When an Mg2+ salt was added to EDTA- or EGTA-containing buffer to give a free Mg2+ concentration of a few micromoles/liter, flow induced polymerization was significantly enhanced. It appears that occupancy of only a small fraction of the high affinity binding sites by Ca2+ prevents flow-polymerization while Mg2+ may enhance this type of polymerization by replacing Ca2+. We speculate that the shear stress induces polymerization by promoting nucleation and that Ca2+ bound to the high affinity divalent cation binding site inhibits formation of the nuclei.

Original languageEnglish
Pages (from-to)118-131
Number of pages14
JournalBBA - Protein Structure
Issue number1
StatePublished - 30 Jan 1981


  • G-Actin
  • Polymerization
  • Shear stress


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