Seryl-tRNA Synthetases: Enzymes with Multiple Personalities*

Seryl-tRNA synthetases (SerRS) are essential enzymes responsible for aminoacylation of cognate transfer-RNAs (tRNAs) with serine, which is then incorporated into the proteins being synthesized on the ribosome. Although tRNA synthetases are usually a very conserved class of enzymes, phylogenic analyses revealed the existence of two distinct types of serine-charging enzymes; a standard or bacterialtype SerRS is found in the majority of organisms (prokaryotes, eukaryotes and archaea), while a highly diverged methanogenic-type SerRS is confined to the methanogenic archaea. We give a short overview on our recent biochemical and structural contributions to the understanding of different molecular mechanisms of tRNA serylation.