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Correlation between calponin and myosin subfragment 1 binding to F-actin and ATPase inhibition
P T Szymanski1, Z Grabarek, T Tao
1Muscle Research Group, Boston Biomedical Research Institute, MA 02114, USA.
Abstract:
Calponin is a thin-filament-associated protein that has been implicated in the regulation of smooth-muscle contractility. It binds to F-actin and inhibits the MgATPase activity of actomyosin. In the present work we have examined the effect of recombinant chicken gizzard alpha-calponin (R alpha CaP) on the binding of rabbit skeletal-muscle myosin subfragment 1 (S1) to F-actin and on the inhibition of its actin-activated MgATPase. We have found that binding of one R alpha CaP molecule to every three to four actin monomers is sufficient for maximal inhibition of acto-S1 ATPase. At this R alpha CaP/actin ratio R alpha CaP does not interfere with S1 binding to F-actin. At higher concentrations, R alpha CaP displaces S1 from F-actin and a 1:1 R alpha CaP-actin monomer complex is formed. R alpha CaP is also able to displace troponin I from its complex with F-actin which may reflect the amino acid sequence similarity between R alpha CaP and troponin I in their actin-binding regions.
Insights
Recombinant chicken gizzard alpha-calponin (R alpha CaP) inhibits actomyosin MgATPase activity by binding to F-actin. Maximal inhibition occurs at a 1:4 R alpha CaP to actin ratio, without affecting myosin subfragment 1 binding.
Area of Science:
- Muscle physiology
- Biochemistry
- Protein-actin interactions
Background:
- Calponin regulates smooth muscle contractility by binding F-actin.
- Calponin inhibits actomyosin MgATPase activity.
Purpose of the Study:
- Investigate the effect of recombinant chicken gizzard alpha-calponin (R alpha CaP) on myosin subfragment 1 (S1) binding to F-actin.
- Determine the impact of R alpha CaP on actin-activated MgATPase inhibition.
Main Methods:
- Utilized recombinant chicken gizzard alpha-calponin (R alpha CaP).
- Examined binding of rabbit skeletal-muscle myosin subfragment 1 (S1) to F-actin.
- Assessed actin-activated MgATPase activity.
Main Results:
- Maximal inhibition of acto-S1 ATPase achieved with one R alpha CaP per 3-4 actin monomers.
- R alpha CaP did not impede S1 binding to F-actin at inhibitory concentrations.
- Higher R alpha CaP concentrations displaced S1, forming a 1:1 R alpha CaP-actin complex.
- R alpha CaP displaced troponin I from F-actin, suggesting sequence similarity.
Conclusions:
- Calponin's inhibitory mechanism involves binding to F-actin.
- The stoichiometry of R alpha CaP binding is crucial for ATPase inhibition.
- R alpha CaP may share actin-binding region similarities with troponin I.