engleski

Phylogenetic relationships and early evolutionary events in seryl-tRNA synthetases

Seryl-tRNA synthetases (SerRS) are homodimeric enzymes that catalyze the ATP-driven formation of an ester bond between serine and tRNASer. They belong to class II aminoacyl-synthetases, which share three common structural motifs. Seryl-tRNA synthetases from diferent organisms exhibit a significant similarity at the sequence level. Our goal was to determine the relationships among known SerRS sequences, including the two SerRS enzymes from maize whose genes we cloned and sequenced recently. Our phylogenetic analyses have revealed that archeal SerRS enzymes are of paraphyletic origin: the sequence of Archaeoglobus SerRS clusters with its eukaryotic cytoplasmic counterparts in accord with the universal tree of life, while the sequences of the known methanobacterial and halobacterial enzymes form a separate clade more closely related to their eubacterial counterparts. This dichotomy is most likely a consequence of an early horizontal gene transfer event. Mitochondrial eukaryotes have a mitochondrial seryl-tRNA synthetase that is evolutionary distant from the cytosolic enzyme. The two known mitochondrial SerRS, from yeast and maize sequences form a marginally significant clade, apparently due to increased mutation rate observed in most proteins with mitochondrial function. It is discussed how this increased mutation rate might have been influenced by interaction of these enzymes with their cognate tRNAs in the mitochondrion. The cytosolic SerRS enzymes of eukaryotes share a common feature - a highly basic C-terminal extension of 18 or more amino acids - that is absent from their eubacterial or mitochondrial counterparts. Sequence divergence among these extensions among different organisms, with preservation of their overall physicochemical properties, suggest that their yet unknown role is mediated through electrostatic interactions. Possible participation of these extensions in aminoacyl-tRNA synthetase complex formation is also addressed.

evolution ; aminoacyl-tRNA synthetases ; phylogenetic analysis

nije evidentirano