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Plasma membrane Ca2+ pump isoforms 2a and 2b are unusually responsive to calmodulin and Ca2+
N L Elwess1, A G Filoteo, A Enyedi
1Department of Biochemistry and Molecular Biology, Mayo Clinic/Foundation, Rochester, Minnesota 55905, USA.
The Journal of Biological Chemistry
|July 18, 1997
Summary
Rat plasma membrane calcium pump isoform 2 (rPMCA2a and rPMCA2b) variants exhibit higher calmodulin affinity and activity than human forms. These rat variants effectively lower cytosolic calcium levels, indicating enhanced cellular calcium regulation.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Physiology
Background:
- Plasma membrane calcium ATPases (PMCAs) regulate intracellular calcium.
- Isoform 2 of rat PMCA (rPMCA2) has two variants: rPMCA2a and rPMCA2b.
- Understanding isoform-specific functions is crucial for cellular calcium homeostasis.
Purpose of the Study:
- To construct and express full-length rPMCA2a and rPMCA2b variants.
- To characterize the calcium transport activity and calmodulin interaction of these rat isoforms.
- To compare their properties with human PMCA isoforms.
Main Methods:
- Expression of rPMCA2a and rPMCA2b in COS-7 cells.
- Determination of calcium transport in a microsomal fraction.
- Analysis of calmodulin affinity and apparent calcium affinity.
Main Results:
- Both rPMCA2a and rPMCA2b showed significantly higher calmodulin affinity than human PMCA4.
- rPMCA2b exhibited the highest calmodulin affinity among tested isoforms.
- rPMCA2a and rPMCA2b demonstrated higher apparent calcium affinity and basal activity, leading to lower free cytosolic Ca2+ levels.
- The enhanced calcium affinity of rPMCA2b was attributed to its carboxyl terminus.
Conclusions:
- Rat PMCA2 variants possess distinct functional properties compared to human isoforms.
- These rPMCA2 variants are potent regulators of cytosolic calcium, capable of maintaining lower free Ca2+ concentrations.
- The carboxyl terminus plays a key role in the high apparent calcium affinity of rPMCA2b.