Rethinking the Evolution of Tubulin Polymerization Promoting Proteins

TPPP (tubulin polymerization promoting protein)-like proteins are found throughout the living world. The individual members of this protein family are distinguished according to how many times and how completely their characteristic structural element, the p25alpha domain, is found in them. Phylogenomic occurrences of the members of the family differ from each other. Animals, fungi, algae, and various groups of unicellular organisms have their characteristic proteins. The two phylogenomic multi-supergroups, Opimoda+ and Diphoda+, show very different patterns in the occurrence of TPPP types. By using BLAST search in protein and nucleotide databases, we found that the previously known phylogenomic distribution is not strictly true, e.g., fungal type TPPPs are not only found in fungi. We primarily analyzed the Opisthokonta clade but also examined broader relationships. It was confirmed that the occurrence of TPPPs/genes is linked to the presence of the eukaryotic flagellum. A TPPP that contains the entire p25alpha domain twice and occurs only in Opisthokonta was identified. We also identified a TPPP in choanoflagellates and in the uncertainly classified Opisthokonta <i>Tunicaraptor unikontis</i>, which was previously known only in the Diphoda+ clade. On the other hand, we found an Opisthokonta (Opimoda+)-specific TPPP in a Heterolobosea (Diphoda+). Based on these results, we need to rethink the evolutionary history of TPPPs.