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Multiple-sited interaction of caldesmon with Ca(2+)-calmodulin
P A Huber1, M El-Mezgueldi, Z Grabarek
1Imperial College, National Heart and Lung Institute, London, U.K.
The Biochemical Journal
|June 1, 1996
Summary
Investigating calcium-calmodulin mutants binding to caldesmon revealed that altered calmodulin structures still bind caldesmon, suggesting other EF-hand proteins can substitute for calmodulin in this interaction.
Area of Science:
- Biochemistry
- Molecular Biology
- Protein-protein interactions
Background:
- Calmodulin (CaM) is a crucial calcium-binding protein regulating various cellular processes.
- Caldesmon is an actin-binding protein that modulates muscle and non-muscle contraction.
- The interaction between CaM and caldesmon is vital for regulating muscle contraction.
Purpose of the Study:
- To investigate the binding of calcium- and barium-calmodulin to caldesmon using wild-type and mutant forms.
- To understand the functional consequences of CaM mutations on caldesmon binding and inhibition.
- To explore the role of specific residues in CaM-caldesmon interaction.
Main Methods:
- Utilized three calmodulin mutants: C41/75, C85/112 (cysteine substitutions), and F92A (phenylalanine substitution).
- Employed native gel electrophoresis and carbodiimide-induced cross-linking for binding assays.
- Assessed functional consequences by measuring the release of caldesmon inhibition on actin-tropomyosin-activated myosin ATPase.
- Conducted NMR spectroscopy and fluorescence spectroscopy to analyze CaM-caldesmon interactions.
Main Results:
- All CaM mutants exhibited reduced affinity for caldesmon compared to wild-type CaM.
- Barium-calmodulin showed further decreased affinity for caldesmon compared to calcium-calmodulin.
- The F92A mutation and Ba2+ substitution abolished CaM's ability to release caldesmon inhibition.
- Cysteine mutants retained functionality but required higher concentrations, reflecting reduced binding affinity.
- Spectroscopic analyses revealed distinct structural changes upon CaM binding to caldesmon fragments.
Conclusions:
- Functional Ca2+-calmodulin binding to caldesmon necessitates multiple interaction sites on both proteins.
- Specific structural modifications in calmodulin do not necessarily abolish caldesmon-related functionality.
- This suggests that various EF-hand proteins may substitute for calmodulin in interacting with caldesmon.