The Calcium Pump of the Plasma Membrane: Structure/Function Relationships
The plasma membrane Ca pump is a P-type ATPase which shares with the other pumps of this type the essential mechanistic properties. At variance with the other pumps of this group, it is activated by calmodulin. It is a single polypeptide chain of molecular mass about 134 kDa, which has now been cloned in both rat and human tissues. It contains ten putative transmembrane domains, and protrudes with most of its mass into the intracellular ambient. The calmodulin binding domain is located next to the C-terminus. Several isoforms of the pump have now been described, differing particularly in the (regulatory) C-terminal portion. In the absence of calmodulin the pump can still be activated by alternative treatments, e.g., the exposure to acidic phospholipids (or polyunsaturated fatty acids), a phosphorylation mediated by the cAMP dependent protein kinase, or a controlled proteolytic treatment, e.g., with trypsin. The latter protease degrades the pump in sequence to fragments of molecular mass 90, 85, 81, and 76 kDa. The 90 to 85 to 81 kDa transition gradually impairs the response to calmodulin and then its binding to the pump. The transition from 81 to 76 kDa abolishes also the response to acidic phospholipids. Trypsin cuts the pump in and around the calmodulin binding domain in producing the fragments of 90 to 81 kDa, between putative transmembrane domains two and three in producing the fragment of 76 kDa.
KeywordsAcidic Phospholipid Putative Transmembrane Domain Calmodulin Binding Domain Pump Molecule Plasma Membrane Calcium Pump
Unable to display preview. Download preview PDF.
- 1.Schatzmann, H.J. (1982) In: “Membrane Transport of Calcium,” E. Carafoli, ed., Acad. Press, London.Google Scholar
- 2.Carafoli, E., Pyshiological Rev. (1990) in press.Google Scholar
- 9.James, P., Maeda, M., Fischer, R., Verma, A.K., Krebs, J., Penniston, J.T. and Carafoli, E. (1980) J. Biol. Chem. 263, 2905–2910.Google Scholar
- 17.Greeb, J., and Shull, G., (1989) J. Biol. Chem. 18569–18576.Google Scholar
- 21.Zvaritch, E., James, P., Vorherr, T., Falchetto, R., Modyanov, N., and Carafoli. E. Biochemistry, (submitted).Google Scholar