We have purified an actin binding protein from amebas of Dictyostelium discoideum which we call 95,000-dalton protein (95K). This protein is rod shaped, approximately 40 nm long in the electron microscope, contains two subunits measuring 95,000 daltons each, and cross-links actin filaments. Cross-linking activity was demonstrated by using falling-ball viscometry, Ostwald viscometry, and electron microscopy. Cross-linking activity is optimal at 0.1 microM Ca++ and pH 6.8, but is progressively inhibited at higher Ca++ and pH levels over a physiological range. Half-maximal inhibition occurs at 1.6 microM free Ca++ and pH 7.3, respectively. Sedimentation experiments demonstrate that elevated Ca++ and pH inhibit the binding of 95K to F-actin which explains the loss of cross-linking activity. Electron microscopy demonstrates that under optimal conditions for cross-linking, 95K protein bundles actin filaments and that this bundling is inhibited by microM Ca++. Severing of actin filaments by 95K was not observed in any of the various assays under any of the solution conditions used. Hence, 95K protein is a rod-shaped, dimeric, Ca++- and pH-regulated actin binding protein that cross-links but does not sever actin filaments.
Article| August 01 1982
A calcium- and pH-regulated protein from Dictyostelium discoideum that cross-links actin filaments.
Online Issn: 1540-8140
Print Issn: 0021-9525
J Cell Biol (1982) 94 (2): 466–471.
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J Condeelis, M Vahey; A calcium- and pH-regulated protein from Dictyostelium discoideum that cross-links actin filaments.. J Cell Biol 1 August 1982; 94 (2): 466–471. doi: https://doi.org/10.1083/jcb.94.2.466
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