Weak binding of divalent cations to plasma gelsolin.
Calcium binding of swine plasma gelsolin was examined. When applied to ion-exchange chromatography, its elution volume was drastically altered depending on the free Ca2+ concentration of the medium. The presence of two classes of Ca2+ binding sites, high-affinity sites (Kd = 7 microM) and low-affinity sites (Kd = 1 mM), was suggested from the concentration dependence of the elution volume. The tight binding sites were specific for Ca2+. The weakly bound Ca2+ could be replaced by Mg2+ once the tight binding sites were occupied with Ca2+. The binding of metal ions was totally reversible. Circular dichroism measurement of plasma gelsolin indicated that most change in secondary structure was associated with Ca2+ binding to the high-affinity sites. Binding of Mg2+ to the low-affinity sites caused a secondary structural change different from that caused by Ca2+ bound to the high-affinity sites. Gel permeation chromatography exhibited a small change in Stokes radius with and without Ca2+. Microheterogeneity revealed by isoelectric focusing did not relate to the presence of two classes of Ca2+ binding sites. These results indicated that plasma gelsolin drastically altered its surface charge property due to binding of Ca2+ or Ca2+, Mg2+ with a concomitant conformational change.
Doi
Y
Y
Department of Food Science, Kyoto Women's University, Japan.
Kim
F
F
Kido
S
S
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000097:blood / Q000378:metabolism*; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D002942:Circular Dichroism; D018260:Gelsolin; D007525:Isoelectric Focusing; D008274:Magnesium / Q000378:metabolism; D008840:Microfilament Proteins / Q000097:blood / Q000378:metabolism*; D011487:Protein Conformation; D013552:Swine
D002135:Calcium-Binding Proteins; D018260:Gelsolin; D008840:Microfilament Proteins; D008274:Magnesium; D002118:Calcium