Calcium-dependent regulation of smooth muscle calponin by S100.
Calponin, a major calmodulin-, actin-, and tropomyosin-binding protein in smooth muscle, interacted with brain S100 and the properties of the interaction were investigated in detail. From fluorescence labeling and chemical cross-linking experiments, the apparent Kd value was calculated to be 7 x 10(7) M-1 in the presence of Ca2+ with 1 mol of S100 bound per mol of calponin. The addition of S100 to the mixture of calponin and F-actin caused the removal of calponin from actin filaments in the presence of Ca2+ but not in the presence of EGTA or Zn2+. Ca2+ and S100 could relieve calponin-induced actomyosin Mg(2+)-ATPase inhibition. Both the removal of calponin from F-actin and the restoration of ATPase inhibition by S100 were more effective than those by calmodulin. At low ionic strength, the binding was observed irrespective of Ca2+ concentration and it was greatly weakened with increasing salt concentration. The formation of the complex in the presence of Ca2+ was less sensitive, with only 45% inhibition at 100 mM NaCl, where the complex in the absence of Ca2+ had almost disappeared. This was confirmed by S-100 Sepharose 4B chromatography. Addition of Ca2+ and S100 also led to a decrease in the affinity of calponin for tropomyosin. Domain mapping with chymotryptic digestion revealed that the S100 binding site resided within the N-terminal 22 kDa fragment of calponin, where the bindings of calmodulin and actin also occur.
Fujii
T
T
Department of Functional Polymer Science, Faculty of Textile Science and Technology, Shinshu University, Nagano.
Oomatsuzawa
A
A
Kuzumaki
N
N
Kondo
Y
Y
D000199:Actins / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002645:Chickens; D004789:Enzyme Activation; D008840:Microfilament Proteins; D009124:Muscle Proteins / Q000378:metabolism*; D009130:Muscle, Smooth / Q000378:metabolism*; D009218:Myosins / Q000378:metabolism; D009418:S100 Proteins / Q000494:pharmacology*; D014335:Tropomyosin / Q000378:metabolism; D000096985:Calponins
D000199:Actins; D002118:Calcium; D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D009218:Myosins; D009418:S100 Proteins; D014335:Tropomyosin; D000096985:Calponins