Acidic-lipid responsive regions of the plasma membrane Ca2+ pump

ADAMO, H.P., DE TEZANOS PINTO, F., BREDESTON, L.M. Y CORRADI, G.R.

ANNALS OF THE NEW YORK ACADEMY OF SCIENCES.

New York Academy of Sciences

Lugar: Nueva York; Año: 2003 vol. 986 p. 552 - 553

0077-8923

The activation of the plasma membrane Ca2+ pump (PMCA) by acidic lipids has been in part accounted for by the finding that they interact with the calmodulin-binding autoinhibitory region (C region). Because these lipids are capable of enhancing the Ca2+ sensitivity of the PMCA to a greater extent than calmodulin, it was suggested that an additional site exists in the region we called AL between transmembrane helices M2 and M3: We have succesfully expressed mutants of the PMCA with deletions in the AL region. Measurements of Ca2+ transport into microsomal vesicles from transfected COS cells showed that mutants with deletions involving amino acids 350-356 were inactive. In contrast, deletion of residues 296-349 resulted in a fully active pump with a high affinity for Ca2+ similar to that of the activated form of the PMCA that would result from the binding of acidic lipids at the AL region. The d(296-349) PMCA was less responsive to phosphatidic acid than the wild type enzyme. These results suggest that the AL region functions as an acidic-lipid binding autoinhibitory region. However, in the presence of calmodulin the activity of the d(296-349) enzyme purified and reconstituted in liposomes still increased with the content of acidic lipids. This result indicate a requirement of acidic lipids for the optimal function of the PMCA not associated with the regulatory domains AL and C.