A novel lipid binding protein is a factor required for MgATP stimulation of the squid nerve Na+/Ca2+ exchanger

ELSO DE BERBERIAN, GRACIELA ;MARIANA BOLLO , GUILLERMO MONTICH , GRETEL ROBERTS , JOSEPH A. DEGIORGIS, REINALDO DIPOLO , LUIS BEAUGÉ

BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES

Elsevier

Año: 2009 vol. 1788 p. 1255 - 1262

0005-2736

Abstract Here we identify a cytosolic factor essential for MgATP up-regulation of the squid nerve Na+/Ca2+ exchanger. Mass spectroscopy and Western blot analysis established that this factor is a member of the lipocalin super family of lipid binding proteins of 132 amino acids in length. We named it Regulatory protein of the squid nerve sodium calcium exchanger (ReP1-NCXSQ). ReP-1-NCXSQ was cloned, over expressed and purified. Far- UV circular dichroism and infrared spectra suggest a majority of â-strand in the secondary structure. Moreover, the predicted tertiary structure indicates ten â-sheets and two short á-helices characteristic of most lipid binding proteins. Functional experiments showed that in order to be active ReP1-NCXSQ must become phosphorylated in the presence of MgATP by a kinase that is Staurosporin insensitive. Even more, the phosphorylated ReP1-NCXSQ is able to stimulate the exchanger in the absence of ATP. In addition to the identification of a new member of the lipid binding protein family, this work shows, for the first time, the requirement of a lipid binding protein for metabolic regulation of an ion transporting system. © 2008 Elsevier B.V. All rights reserved.