A novel lipid binding protein is a factor required for MgATP stimulation of the squid nerve Na+/Ca2+ exchanger
DeGiorgis, Joseph A.
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KeywordNa+/Ca2+ counter-transport; Transport regulation; Lipid binding proteins; Membrane transporters; Squid nerve
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 β-strand in the secondary structure. Moreover, the predicted tertiary structure indicates ten β-sheets and two short α- 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.
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Biochimica et Biophysica Acta - Biomembranes 1788 (2009): 1255-1262, doi:10.1016/j.bbamem.2008.12.016.
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