Plasma Membrane Calcium Pump (PMCA) Differential Exposure of Hydrophobic Domains after Calmodulin and Phosphatidic Acid Activation (original) (raw)

2011, Journal of Biological Chemistry

The exposure of the plasma membrane calcium pump (PMCA) to the surrounding phospholipids was assessed by measuring the incorporation of the photoactivatable phosphatidylcholine analog [ 125 I]TID-PC/16 to the protein. In the presence of Ca 2؉ both calmodulin (CaM) and phosphatidic acid (PA) greatly decreased the incorporation of [ 125 I]TID-PC/16 to PMCA. Proteolysis of PMCA with V8 protease results in three main fragments: N, which includes transmembrane segments M1 and M2; M, which includes M3 and M4; and C, which includes M5 to M10. CaM decreased the level of incorporation of [ 125 I]TID-PC/16 to fragments M and C, whereas phosphatidic acid decreased the incorporation of [ 125 I]TID-PC/16 to fragments N and M. This suggests that the conformational changes induced by binding of CaM or PA extend to the adjacent transmembrane domains.