TY - JOUR
T1 - A calciumdiscoideum and pH-regulated protein from dictyostelium that cross-links actin filaments
AU - Condeelis, John
AU - Vahey, Maryanne
PY - 1982/8/1
Y1 - 1982/8/1
N2 - 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, ~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 µM 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 µM free Ca++ and pH 7.3, respectively. Sedimentation experiments demonstrate that elevated Ca++ and pH inhibit the binding of 95K to Factin 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 µM 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.
AB - 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, ~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 µM 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 µM free Ca++ and pH 7.3, respectively. Sedimentation experiments demonstrate that elevated Ca++ and pH inhibit the binding of 95K to Factin 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 µM 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.
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U2 - 10.1083/jcb.94.2.466
DO - 10.1083/jcb.94.2.466
M3 - Article
C2 - 7107709
AN - SCOPUS:0019975940
SN - 0021-9525
VL - 94
SP - 466
EP - 471
JO - Journal of Cell Biology
JF - Journal of Cell Biology
IS - 2
ER -