Conformational changes produced by ATP binding to the plasma membrane calcium pump

IC MANGIALAVORI; M. FERREIRA GOMES; NA. SAFFIOTI; RM GONZALEZ LEBRERO; RC ROSSI; JPFC ROSSI

JOURNAL OF BIOLOGICAL CHEMISTRY

AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC

Lugar: Bethesda, Maryland; Año: 2013 vol. 288 p. 31030 - 31041

0021-9258

The aim of this work was to study the plasma membrane calcium pump (PMCA) reaction cycle by characterising conformational changes associated with calcium, ATP and vanadate binding to purified PMCA. This was accomplished by studying the exposure of PMCA to surrounding phospholipids by measuring the incorporation of the photoactivatable phosphatidylcholine analog [125I]TID-PC/16 to the protein. ATP could bind to the different vanadate-bound states of the enzyme either in the presence or in the absence of Ca2+ with high apparent affinity.Conformational movements of the ATP binding domain were determined using the fluorescent analog TNP-ATP. To assess the conformational behaviour of the Ca2+ binding domain we also studied the occlusion of Ca2+, both in the presence and in the absence of ATP and with or without vanadate. Results show the existence of occluded species in the presence of vanadate and/or ATP. This allowed the development of a model that describes the transport of Ca2+ and its relation with ATP hydrolysis.This is the first approach which uses a conformational study to describe thePMCA P-type ATPase reaction cycle, adding important features to the classical E1-E2 model devised using kinetics methodology only.