Journal
FEBS LETTERS
Volume 546, Issue 2-3, Pages 359-364Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S0014-5793(03)00634-3
Keywords
acidic phospholipid; actin binding; calcium signaling; membrane binding
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Annexin A9 is a novel member of the annexin family of Ca2+ and phospholipid binding proteins which has so far only been identified in EST data bases and whose deduced protein sequence shows mutations in residues considered crucial for Ca2+ coordination in other annexins. To elucidate whether the annexin A9 protein is expressed as such and to characterize its biochemical properties we probed cell extracts with specific anti-annexin A9 antibodies and developed a recombinant expression system. We show that the protein is found in HepG2 hepatoma cell lysates and that a green fluorescent protein-tagged form is abundantly expressed in the cytosol of HeLa cells. Recombinant expression in bacteria yields a soluble protein that can be enriched by conventional chromatographic procedures. The protein is capable of binding phosphatidylserine containing liposomes albeit only at Ca2+ concentrations exceeding 2 mM. Moreover and in contrast to other annexins this binding appears to be irreversible as the liposome-bound annexin A9 cannot be released by Ca2+ chelation. These results indicate that annexin A9 is a unique member of the annexin family whose intracellular activity is not subject to Ca2+ regulation. (C) 2063 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.
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