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

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.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.The work was supported by Grants from the US National Science Foundation [MCB 0444598], Fondo Nacional para Investigaciones Científicas y Tecnológicas [PICT-05- 12397 and PICT-05-38073], Consejo Nacional de Investigfaciones Científicas y Técnicas [PIP 5118 and PIP 5593] Secretaría de Ciencia y Técnica Universidad Nacional de Córdoba, Argentina, Fondo Nacional para Ciencia y Técnica [S1-9900009046 and G- 2001000637] and Fundación Polar, Venezuela and The Rhode Island Idea Network of Biomedical Research Excellence (INBRE)

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In recent studies on prenatal testing for Noonan syndrome (NS) in fetuses with an increased nuchal translucency (NT) and a normal karyotype, mutations have been reported in 9-16% of cases. In this study, DNA of 75 fetuses with a normal karyotype and abnormal ultrasound findings was tested in a diagnostic setting for mutations in (a subset of) the four most commonly mutated NS genes. A de novo mutation in either PTPN11, KRAS or RAF1 was detected in 13 fetuses (17.3%). Ultrasound findings were increased NT, distended jugular lymphatic sacs (JLS), hydrothorax, renal anomalies, polyhydramnios, cystic hygroma, cardiac anomalies, hydrops fetalis and ascites. A second group, consisting of anonymized DNA of 60 other fetuses with sonographic abnormalities, was tested for mutations in 10 NS genes. In this group, five possible pathogenic mutations have been identified (in PTPN11 (n=2), RAF1, BRAF and MAP2K1 (each n=1)). We recommend prenatal testing of PTPN11, KRAS and RAF1 in pregnancies with an increased NT and at least one of the following additional features: polyhydramnios, hydrops fetalis, renal anomalies, distended JLS, hydrothorax, cardiac anomalies, cystic hygroma and ascites. If possible, mutation analysis of BRAF and MAP2K1 should be considered