Annexin XXI (ANX21) of Giardia lamblia has sequence motifs uniquely shared by giardial annexins and is specifically localized in the flagella

Abstract

We have identified a novel annexin, ANX21, in trophozoites of Giardia lamblia. The nucleotide sequence encoding this protein deviated from a published sequence in predicting an additional endonexin fold in the fourth annexin domain. In addition, several motifs exclusively shared by other annexins of G. lamblia in their predicted fourth repeat and predicted to be localized on the opposite (concave) surface of the molecule became apparent. Western blots of trophozoite fractions probed with antiserum against the recombinant protein indicated that this annexin, like the other giardial annexins ANX19 and ANX20, associates with phospholipids in the presence of Ca2+. Finally, confocal laser scanning of trophozoites showed that the protein, apart from the median body, was exclusively localized in the eight flagella. Together, these data suggest that ANX21 may function as a Ca2+-regulated structural element linking phospholipid bilayer and underlying axoneme.