Divergent Evolution of Eukaryotic CC- and A-Adding Enzymes

• Main Authors: Lieselotte Erber, Paul Franz, Heike Betat, Sonja Prohaska, Mario Mörl
• Format: Article
• Language: English
• Published: MDPI AG 2020-01-01
• Series: International Journal of Molecular Sciences
• Subjects: trna nucleotidyltransferase; enzyme evolution; <i>salpingoeca rosetta</i>; <i>schizosaccharomyces pombe</i>
• Online Access: https://www.mdpi.com/1422-0067/21/2/462

Synthesis of the CCA end of essential tRNAs is performed either by CCA-adding enzymes or as a collaboration between enzymes restricted to CC- and A-incorporation. While the occurrence of such tRNA nucleotidyltransferases with partial activities seemed to be restricted to Bacteria, the first example of such split CCA-adding activities was reported in <i>Schizosaccharomyces pombe</i>. Here, we demonstrate that the choanoflagellate <i>Salpingoeca rosetta</i> also carries CC- and A-adding enzymes. However, these enzymes have distinct evolutionary origins. Furthermore, the restricted activity of the eukaryotic CC-adding enzymes has evolved in a different way compared to their bacterial counterparts. Yet, the molecular basis is very similar, as highly conserved positions within a catalytically important flexible loop region are missing in the CC-adding enzymes. For both the CC-adding enzymes from <i>S. rosetta</i> as well as <i>S. pombe</i>, introduction of the loop elements from closely related enzymes with full activity was able to restore CCA-addition, corroborating the significance of this loop in the evolution of bacterial as well as eukaryotic tRNA nucleotidyltransferases. Our data demonstrate that partial CC- and A-adding activities in Bacteria and Eukaryotes are based on the same mechanistic principles but, surprisingly, originate from different evolutionary events.