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Plasma membrane Ca(2+) pump isoform 3f is weakly stimulated by calmodulin
A G Filoteo1, A Enyedi, A K Verma
1Department of Biochemistry and Molecular Biology, Mayo Foundation, Rochester, Minnesota 55905, USA.
The Journal of Biological Chemistry
|February 8, 2000
Summary
Plasma membrane Ca(2+) pump isoform 3f in rat skeletal muscle has a unique, short regulatory region. This isoform functions as a constitutively active enzyme, unlike other isoforms.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Physiology
Background:
- The plasma membrane Ca(2+) pump (PMCA) plays a crucial role in calcium homeostasis.
- Different PMCA isoforms exhibit distinct structural and functional properties.
- Isoform 3f, prevalent in rat skeletal muscle, possesses an atypical regulatory domain.
Purpose of the Study:
- To investigate the structural and functional characteristics of plasma membrane Ca(2+) pump isoform 3f.
- To determine the calmodulin binding affinity and regulatory role of isoform 3f's carboxyl-terminal region.
- To elucidate the catalytic activity and regulation of isoform 3f compared to other isoforms.
Main Methods:
- Peptide synthesis to represent the calmodulin binding domain.
- Construction and analysis of chimeric and full-length isoform 3f.
- Calmodulin binding assays using calmodulin-Sepharose.
- Enzyme activity measurements with and without calmodulin.
Main Results:
- Isoform 3f exhibits significantly lower calmodulin affinity compared to isoform 2b.
- A chimera of isoform 3f's regulatory region and isoform 4's catalytic core was constitutively active.
- Full-length isoform 3f showed minimal activation by calmodulin, indicating weak autoinhibition.
Conclusions:
- The regulatory region of PMCA isoform 3f acts as a weak autoinhibitor.
- Isoform 3f represents a constitutively active form of the Ca(2+) pump, primarily in skeletal muscle.
- Its unique structure facilitates a specialized, always-on function in calcium regulation.