Primary structure and expression of the Xenopus laevis gene encoding annexin II

Annexin II (AnxII) is one of the Ca(2+)-dependent membrane- and phospholipid-binding proteins (annexins) which are encoded by a multigene family. AnxII was originally described as a major cellular substrate for the tyrosine kinase encoded by the src oncogene, and is also phosphorylated by protein kinase C in vivo and in vitro. To obtain more information about structurally conserved regions in AnxII, which could be of structural and/or functional importance, we have identified AnxII in a nonmammalian species, the clawed toad Xenopus laevis. In a ligand overlay assay, we employed p11, the cellular protein ligand of AnxII, to show that a 36-kDa Anx capable of binding p11 is present in a cellular extract from X. laevis cells. The cDNA cloning and sequence analysis revealed that two types of AnxII mRNA are expressed in X. laevis. The transcripts are highly similar to each other, but are encoded by two different genes. The deduced amino acid sequences show a high degree of conservation when compared to the sequences of mammalian and chicken AnxII. In particular, the p11-binding domain, as well as the protein core, which harbors the binding sites for Ca2+ and phospholipid, are highly similar. However, Tyr23, which is phosphorylated by pp60src in mammalian and chicken AnxII, is replaced by a Leu residue in both X. laevis molecules. Thus, tyrosine phosphorylation is probably not a general mode of regulation of AnxII function(s).