Related Experiment Videos
Tyrosine phosphorylation modulates the interaction of calmodulin with its target proteins
C Corti1, E Leclerc L'Hostis, M Quadroni
1Protein Chemistry Laboratory, Department of Biology, Swiss Federal Institute of Technology, (ETH) Zürich.
Abstract:
The activation of six target enzymes by calmodulin phosphorylated on Tyr99 (PCaM) and the binding affinities of their respective calmodulin binding domains were tested. The six enzymes were: myosin light chain kinase (MLCK), 3'-5'-cyclic nucleotide phosphodiesterase (PDE), plasma membrane (PM) Ca2+-ATPase, Ca2+-CaM dependent protein phosphatase 2B (calcineurin), neuronal nitric oxide synthase (NOS) and type II Ca2+-calmodulin dependent protein kinase (CaM kinase II). In general, tyrosine phosphorylation led to an increase in the activatory properties of calmodulin (CaM). For plasma membrane (PM) Ca2+-ATPase, PDE and CaM kinase II, the primary effect was a decrease in the concentration at which half maximal velocity was attained (Kact). In contrast, for calcineurin and NOS phosphorylation of CaM significantly increased the Vmax. For MLCK, however, neither Vmax nor Kact were affected by tyrosine phosphorylation. Direct determination by fluorescence techniques of the dissociation constants with synthetic peptides corresponding to the CaM-binding domain of the six analysed enzymes revealed that phosphorylation of Tyr99 on CaM generally increased its affinity for the peptides.
Insights
Tyrosine phosphorylation of calmodulin enhances its ability to activate target enzymes like calcineurin and nitric oxide synthase. This modification also increases calmodulin's binding affinity for enzyme domains, impacting enzyme kinetics.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- Calmodulin (CaM) is a crucial calcium-binding protein that regulates numerous cellular processes by interacting with various target enzymes.
- Post-translational modifications, such as phosphorylation, can alter calmodulin's structure and function.
- Phosphorylation of calmodulin on tyrosine residues (Tyr99) is a specific modification with potential implications for enzyme activation and binding.
Purpose of the Study:
- To investigate the effect of Tyr99-phosphorylated calmodulin (PCaM) on the activation of six key target enzymes.
- To determine how PCaM affects the binding affinities between calmodulin and the calmodulin-binding domains of these enzymes.
- To elucidate the kinetic changes (Kact and Vmax) induced by PCaM in the studied enzymes.
Main Methods:
- Enzyme activity assays were performed to measure the activation of six target enzymes by PCaM.
- Kinetic parameters, including Kact (half-maximal activation constant) and Vmax (maximal velocity), were determined.
- Fluorescence techniques were utilized to directly measure the dissociation constants between PCaM and synthetic peptides representing the calmodulin-binding domains of the enzymes.
Main Results:
- Tyrosine phosphorylation of CaM generally enhanced its activatory properties across the tested enzymes.
- For plasma membrane Ca2+-ATPase, PDE, and CaM kinase II, PCaM primarily decreased the Kact, indicating increased sensitivity.
- For calcineurin and NOS, PCaM significantly increased Vmax, suggesting enhanced catalytic rates. MLCK activity was unaffected.
- PCaM generally exhibited increased binding affinity for the calmodulin-binding domains of the analyzed enzymes.
Conclusions:
- Tyrosine phosphorylation at Tyr99 is a significant regulatory mechanism for calmodulin function.
- PCaM modulates the activity of various enzymes through altered kinetic parameters and enhanced binding affinity.
- These findings highlight the role of CaM phosphorylation in fine-tuning cellular signaling pathways.