Metabolic regulation of the squid nerve Na(+)/Ca (2+) exchanger: recent developments. 2013

Luis Beaugé, and Reinaldo Dipolo, and Mariana Bollo, and Alexandra Cousido, and Graciela Berberián, and Alberto Podjarny
Laboratorio de Biofísica, Instituto de Investigación Médica, Córdoba, Argentina. lbeauge@immf.uncor.edu

In squid nerves, MgATP modulation of the Na(+)/Ca(2+) exchanger requires the presence of a cytosolic protein which becomes phosphorylated during the process. This factor has been recently identified. Mass spectroscopy and Western blot analysis established that it is a member of the lipocalin superfamily of lipid-binding proteins (LBP or FABP) of 132 amino acids. We called it regulatory protein of squid nerve sodium/calcium exchanger (ReP1-NCXSQ, access to GenBank EU981897).ReP1-NCXSQ was cloned, expressed, and purified. Circular dichroism, far-UV, and infrared spectroscopy suggest a secondary structure, predominantly of beta-sheets. The tertiary structure prediction provides ten beta-sheets and two alpha-helices, characteristic of most of LPB. Functional experiments showed that, to be active, ReP1-NCXSQ must be phosphorylated by MgATP, through the action of a kinase present in the plasma membrane. Moreover, PO4-ReP1-NCXSQ can stimulate the exchanger in the absence of ATP. An additional crucial observation was that, in proteoliposomes containing only the purified Na(+)/Ca(2+) exchanger, PO4-ReP1-NCXSQ promotes activation; therefore, this upregulation has no other requirement than a lipid membrane and the incorporated exchanger protein.Recently, we solved the crystal structure of ReP1-NCXSQ which was as predicted: a "barrel" consisting of ten beta-sheets and two alpha-helices. Inside the barrel is the fatty acid coordinated by hydrogen bonds with Arg126 and Tyr128. Point mutations showed that neither Tyr20Ala, Arg58Val, Ser99Ala, nor Arg126Val is necessary for protein phosphorylation or activity. On the other hand, Tyr128 is essential for activity but not for phosphorylation. We can conclude that (1) for the first time, a role of an LBP is demonstrated in the metabolic regulation of an ion exchanger; (2) phosphorylation of this LBP can be separated from the activation capacity; and (3) Tyr128, a candidate to coordinate lipid binding inside the barrel, is essential for activity.

UI MeSH Term Description Entries
D009419 Nerve Tissue Proteins Proteins, Nerve Tissue,Tissue Proteins, Nerve
D010766 Phosphorylation The introduction of a phosphoryl group into a compound through the formation of an ester bond between the compound and a phosphorus moiety. Phosphorylations
D002462 Cell Membrane The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells. Plasma Membrane,Cytoplasmic Membrane,Cell Membranes,Cytoplasmic Membranes,Membrane, Cell,Membrane, Cytoplasmic,Membrane, Plasma,Membranes, Cell,Membranes, Cytoplasmic,Membranes, Plasma,Plasma Membranes
D003001 Cloning, Molecular The insertion of recombinant DNA molecules from prokaryotic and/or eukaryotic sources into a replicating vehicle, such as a plasmid or virus vector, and the introduction of the resultant hybrid molecules into recipient cells without altering the viability of those cells. Molecular Cloning
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D017433 Protein Structure, Secondary The level of protein structure in which regular hydrogen-bond interactions within contiguous stretches of polypeptide chain give rise to ALPHA-HELICES; BETA-STRANDS (which align to form BETA-SHEETS), or other types of coils. This is the first folding level of protein conformation. Secondary Protein Structure,Protein Structures, Secondary,Secondary Protein Structures,Structure, Secondary Protein,Structures, Secondary Protein
D017434 Protein Structure, Tertiary The level of protein structure in which combinations of secondary protein structures (ALPHA HELICES; BETA SHEETS; loop regions, and AMINO ACID MOTIFS) pack together to form folded shapes. Disulfide bridges between cysteines in two different parts of the polypeptide chain along with other interactions between the chains play a role in the formation and stabilization of tertiary structure. Tertiary Protein Structure,Protein Structures, Tertiary,Tertiary Protein Structures
D049832 Decapodiformes A superorder of CEPHALOPODS comprised of squid, cuttlefish, and their relatives. Their distinguishing feature is the modification of their fourth pair of arms into tentacles, resulting in 10 limbs. Cuttlefish,Illex,Sepiidae,Squid,Todarodes,Cuttlefishs,Decapodiforme,Illices,Squids,Todarode
D050556 Fatty Acid-Binding Proteins Intracellular proteins that reversibly bind hydrophobic ligands including: saturated and unsaturated FATTY ACIDS; EICOSANOIDS; and RETINOIDS. They are considered a highly conserved and ubiquitously expressed family of proteins that may play a role in the metabolism of LIPIDS. Fatty Acid-Binding Protein,Adipocyte Lipid Binding Protein,Adipocyte-Specific Fatty Acid-Binding Protein,Brain-Type Fatty Acid-Binding Protein,Cytosolic Lipid-Binding Proteins,Fatty Acid-Binding Protein, Cardiac Myocyte,Fatty Acid-Binding Protein, Myocardial,Fatty Acid-Binding Proteins, Adipocyte-Specific,Fatty Acid-Binding Proteins, Brain-Specific,Fatty Acid-Binding Proteins, Cytosolic-Specific,Fatty Acid-Binding Proteins, Intestinal-Specific,Fatty Acid-Binding Proteins, Liver-Specific,Fatty Acid-Binding Proteins, Myocardial-Specific,Fatty Acid-Binding Proteins, Plasma-Membrane Specific,Intestinal Fatty Acid-Binding Protein,Liver Fatty Acid-Binding Protein,Myocardial Fatty Acid-Binding Protein,Plasma Membrane Fatty Acid-Binding Protein,Acid-Binding Protein, Fatty,Adipocyte Specific Fatty Acid Binding Protein,Brain Type Fatty Acid Binding Protein,Cytosolic Lipid Binding Proteins,Fatty Acid Binding Protein,Fatty Acid Binding Protein, Cardiac Myocyte,Fatty Acid Binding Protein, Myocardial,Fatty Acid Binding Proteins,Fatty Acid Binding Proteins, Adipocyte Specific,Fatty Acid Binding Proteins, Brain Specific,Fatty Acid Binding Proteins, Cytosolic Specific,Fatty Acid Binding Proteins, Intestinal Specific,Fatty Acid Binding Proteins, Liver Specific,Fatty Acid Binding Proteins, Myocardial Specific,Fatty Acid Binding Proteins, Plasma Membrane Specific,Intestinal Fatty Acid Binding Protein,Lipid-Binding Proteins, Cytosolic,Liver Fatty Acid Binding Protein,Myocardial Fatty Acid Binding Protein,Plasma Membrane Fatty Acid Binding Protein,Protein, Fatty Acid-Binding
D019831 Sodium-Calcium Exchanger An electrogenic ion exchange protein that maintains a steady level of calcium by removing an amount of calcium equal to that which enters the cells. It is widely distributed in most excitable membranes, including the brain and heart. Ca(2+)-Na(+) Exchanger,Calcium-Sodium Carrier,Calcium-Sodium Exchanger,Na(+)-Ca(2+) Exchanger,Sodium-Calcium Carrier,Ca(2+)-Na(+) Antiporter,Calcium-Sodium Antiporter,Na(+)-Ca(2+) Antiporter,Sodium-Calcium Antiporter,Antiporter, Calcium-Sodium,Antiporter, Sodium-Calcium,Calcium Sodium Antiporter,Calcium Sodium Carrier,Calcium Sodium Exchanger,Carrier, Calcium-Sodium,Carrier, Sodium-Calcium,Exchanger, Calcium-Sodium,Exchanger, Sodium-Calcium,Sodium Calcium Antiporter,Sodium Calcium Carrier,Sodium Calcium Exchanger

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