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Characterization of calponin binding to actin
F W Lu1, M V Freedman, J M Chalovich
1Department of Biochemistry, East Carolina University School of Medicine, Greenville, North Carolina 27858-4354, USA.
Biochemistry
|September 19, 1995
Summary
Calponin binding to actin is dependent on ionic strength, shifting from a 1:1 ratio at lower concentrations to 1:2 at higher concentrations. This protein also influences actin bundling and displaces caldesmon in complexes.
Area of Science:
- Biochemistry
- Cell Biology
- Muscle Physiology
Background:
- Calponin inhibits myosin's actin-activated ATPase activity.
- Previous studies reported variable calponin-to-actin binding stoichiometry.
Purpose of the Study:
- To detail the binding characteristics of calponin to actin.
- To investigate the influence of ionic strength on calponin-actin stoichiometry.
Main Methods:
- Utilized [14C]iodoacetamide-labeled calponin for binding studies.
- Investigated binding stoichiometry and affinity across varying ionic strengths.
- Observed effects of calponin on actin bundling and caldesmon displacement.
Main Results:
- Calponin-actin stoichiometry varied with ionic strength: 1:1 below 110 mM, shifting to 1:2 above 110 mM.
- At physiological ionic strength, binding showed positive cooperativity with an association constant of 6 x 10(6) M-1.
- Calponin binding affinity decreased by 80% in the presence of ATP.
- Actin bundling occurred when calponin saturation exceeded 30%.
- Calponin displaced caldesmon from actin-caldesmon complexes.
Conclusions:
- Calponin's interaction with actin is sensitive to ionic strength and ATP.
- Calponin plays a role in actin organization and may modulate actin-binding protein interactions.