Lipid-protein interactions in Plasma membrana Calcium Pump

MANGIALAVORI IRENE CECILIA, VILLAMIL GIRALDO ANA MARÍA AND ROSSI JUAN PABLO FC

Rosario. Santa Fe. Argentina

Congreso; • XXXV Reunión Anual de la Sociedad Argentina de Biofísica (SAB); 2006

Sociedad Argentina de Biofísica

The plasma membrane calcium pump (PMCA) is an integral membrane protein that functions to maintain the low intracellular Ca2+ necessary for signal [1 and 2], transporting this ion across the cellular membrane. The energy necessary for this transport provide of ATP hydrolysis. The PMCA is a 134KDa protein with 10 transmembrane segments [3]. A large loop located between transmembrane segments 4 and 5 contains ATP-binding site and phosphotytable aspartate residue.  [4]. The CaM-binding domain is located near the C-terminus of PMCA. As many other membrane proteins, PMCA is particularly sensitive to its phospholipids environment, hence acidic phospholipids increase their activity [5]; but the principal regulator mechanism of enzymatic activity is the calmodulin-binding. This region has been suggested to function as an autoinhibitory domain that regulated activity of the pump by binding to a region closely to catalytic site [6]. Therefore, CaM binding leads to dissociation of this domain, cause a large conformational change allowing the activation of PMCA.    With the objective of evaluate if this change conformational produced by calmodulin-binding modify the PMCA surface in contact with lipids, we have employed the photoactivable phosphatidylcholine analogue [125I] TID-PC/16 on the enzyme reconstituted in detergent micelles or, detergent and PC micelles. Thus, we accounted the surface PMCA in contact with anphiphiles when calmodulin is or not united to the pump. Our results show that the major interaction with anphiphiles is when calmodulin isn’t binding PMCA; this suggests that the enzyme in basal conditions (autoinhibited) have high interaction with plasma membrane. This difference of interaction respect of binding-calmodulin is the same yet was evaluate the displacement effect of reactive for PC, obtaining as expected any important decreases of the radioactive mark but preserving the relationship between both conditions.