Acidic-Lipid Responsive Regions of the Plasma Membrane Ca2+ Pump

ADAMO. H P; DE TEZANOS PINTO F; BREDESTON L.M; CORRADI G

Elsimore, DenmarK

Conferencia; “10 th INTERNATIONAL CONFERENCE ON Na, K-ATPase AND RELATED CATION PUMPS”; 2002

The activation off the plasma menbrane 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 successfully 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(296-249) enzyme purified and reconstituted in liposomes still increased with the content of acidic lipids. This result indicate a requeriment of acidic lipids for the optimal function of the PMCA not associated with the regulatory domains AL and C.