Atypical properties displayed by annexin A9, a novel member of the annexin family of Ca(2+) and lipid binding proteins.
Annexin A9 is a novel member of the annexin family of Ca(2+) 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 Ca(2+) 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 Ca(2+) 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 Ca(2+) chelation. These results indicate that annexin A9 is a unique member of the annexin family whose intracellular activity is not subject to Ca(2+) regulation.
Goebeler
Verena
V
Institute of Medical Biochemistry, Centre for Molecular Biology of Inflammation, University of Münster, von-Esmarch-Str 56, D-48149 Münster, Germany.
Ruhe
Daniela
D
Gerke
Volker
V
Rescher
Ursula
U
D017302:Annexins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D050356:Lipid Metabolism; D008164:Luminescent Proteins / Q000378:metabolism; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D017302:Annexins; D018076:DNA, Complementary; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D049452:Green Fluorescent Proteins; D002118:Calcium