Annexin B1 from Taenia solium metacestodes is a newly characterized member of the annexin family.

We previously reported cloning of the Taenia solium annexin B1 gene from a metacestode cDNA expression library and demonstrated that it acts as a protective antigen for effective vaccine development against cysticercosis. In the present study we produced recombinant annexin B1 and antiserum against the protein to investigate its structural and functional properties. Western blotting of metacestode fractions indicated that T. solium annexin B1, similar to vertebrate annexins, associates with acid phospholipids in the presence of Ca(2+). This property was confirmed by the recognition of apoptotic cells by labeled annexin B1. CD spectroscopy results demonstrated that alpha-helices are the main secondary structures of the protein. Ca(2+) binding increases the alpha-helix content and causes significant thermal stabilization with a melting temperature increase of approximately 10 degrees C. Functional Ca(2+)-dependent phospholipid binding sites of annexin B1 were investigated using mutant proteins. By changing a conserved acidic amino acid residue that putatively combines Ca(2+) in each domain of annexin B1 singly or in combination, we found that Ca(2+) binding in the first domain is more important than that at the other Ca(2+) binding sites. Annexin B1 is a metacestode stage-specific antigen, with the protein being mainly localized in the teguments and surrounding cyst wall of T. solium metacestodes, suggesting a role in the parasite-host interaction.