Atypical properties displayed by annexin A9, a novel member of the annexin family of Ca²⁺ and lipid binding proteins

Abstract

Annexin A9 is a novel member of the annexin family of Ca 2+ and phospholipid binding proteins which has so far only been identi¢ed 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 speci¢c antiannexin A9 antibodies and developed a recombinant expression system. We show that the protein is found in HepG2 hepatoma cell lysates and that a green £uorescent 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 Ca2+ regulation.

Selective Ablation of the Androgen Receptor in Mouse Sertoli Cells Affects Sertoli Cell Maturation, Barrier Formation and Cytoskeletal Development

“…These proteins have been implicated in membrane organization, membrane-cytoskeleton contacts and vesicular transport. A unique feature of ANXA9 is that its Ca ++ -binding sites are dysfunctional and accordingly its function is unknown [66]. Interestingly, its promoter binds GATA1 [67], an important transcription factor in SC, the expression of which we monitored in our samples.…”

IL‐22 regulates the expression of genes responsible for antimicrobial defense, cellular differentiation, and mobility in keratinocytes: a potential role in psoriasis

“…The intracellular C-domain and CIS region of DSC1 mediate interactions with placoglobin and desmoplakin, respectively. ANXA9 is a novel member of the annexin family that binds phosphatidylserine in a calcium-dependent manner [43]. Members of the annexin family play a role in the regulation of actin dynamics.…”

Annexins – unique membrane binding proteins with diverse functions

“…However, we must consider variations of this theme because some annexins can interact with membranes in the absence of Ca 2+ (reviewed by Gerke and Moss, 2002). Moreover, some annexins, such as annexin A9, annexin A10 and the Caenorhabditis elegans annexin NEX4, lack highaffinity Ca 2+ -binding sites, which indicates that they are probably not affected by intracellular Ca 2+ fluctuations (Goebeler et al, 2003;Morgan and Fernandez, 1998;Morgan et al, 1999).…”