Evolution of thioester-containing proteins revealed by cloning and characterization of their genes from a cnidarian sea anemone, Haliplanella lineate.

To elucidate the evolutionary origin of genes encoding thioester-containing proteins (TEPs), TEP genes were isolated from a cnidarian, a sea anemone, Haliplanella lineate. Phylogenetic tree analysis of the four identified cnidarian TEP genes and various TEP genes of many metazoa, indicated that they could be classified into two subfamilies: the alpha-2-macroglobulin (A2M) subfamily encodining A2M, CD109 and insect TEPs, and the C3 subfamily encoding complement C3, C4 and C5. Two of the four cnidarian TEP genes belonged to the A2M subfamily, showing a close similarity to human A2M and CD109, respectively and thus were termed HaliA2M and HaliCD109. The other two genes belonged to the C3 subfamily, and were termed HaliC3-1 and HaliC3-2. Cnidarian TEPs retained the basic domain structure and functionally important residues for each molecule, and their mRNA were detected at different parts of the sea anemone body. These results suggest that gene duplication and subsequent functional differentiation among C3, A2M and CD109 were very ancient events predating the divergence of the cnidaria and bilateria.