The natural polyphenol, epigallocatechin-3-gallate, inhibits the Plasma Membrane Ca2+-ATPase by favoring the phosphoenzyme conformation

RINALDI D.; SAFFIOTI N. A.; MANGIALAVORI I. C.; REY O.; ROSSI R. C.; FERREIRA GOMES M. S.; ROSSI J. P. F. C.

Congreso; III Latin American Federation of Biophysical Societies (LAFeBS) ? IX IberoAmerican Congress of Biophysics ? XLV Reunion Anual SAB 2016; 2016

Epigallocatechin 3-gallate (EGCG) is the major polyphenol component of green tea. This compound is believed to be the main responsible for many of the health benefits associated with green tea. EGCG beneficial effects include antioxidant, anti-inflammatory and neuroprotective effects. EGCG produces alterations in intracellular Ca2+ homeostasis which could be linked to the function of the Sarcoplasmic Reticulum Calcium Pump (SERCA). The maintenance of intracellular calcium levels is fine-tuned by the Plasma Membrane Ca2+-ATPase (PMCA). Therefore, we investigated the effect of different flavan-3-ols and went into detail about the EGCG effect on PMCA. We performed measurements of the Ca2+-ATPase activity on PMCA purified from human red blood cells and of Ca2+ flux on HEK293T cells that overexpress PMCA4. We evaluated PMCA ATPase activity in the presence of catechin (C), epicatechin (EC) and epigallocatechin. C and EC showed no effect up to 100 M. However, EGCG showed a strong inhibition with a K0:5 of 0.032 0.003 M. Under similar conditions, EGCg showed an increase of the phosphorylated intermediate which was found to be ADP sensitive, suggesting that EGCG could stabilize the E1P conformation on the reaction cycle of hydrolysis of ATP by PMCA. We performed docking assays of EGCG as ligand and PMCA structuremodels as the receptor. PMCA models were obtained by homology modelling on SERCA crystallographic structures in different conformations. Our results showed that ECGC binds mainly to the closed conformations of the enzyme. Particularly the E1P conformation forms the lowest free energy biding complexes with the ligand establishing hydrogen bonds with both the P and N domains of the pump. On the other hand, Ca2+ eflux in HEK293 cells is inhibited by EGCG in vivo showing its physiological relevance on PMCA activity.