engleski

Structure, function and evolution of seryl-tRNA synthetases

Seryl-tRNA synthetase (SerRS) plays the essential role in all organisms of aminoacylating cognate tRNASer with serine. There are four particularly interesting aspects of the serine system. Firstly the existence of six serine codons in two distinct codon groups implies that there is no consistent anti-codon nucleotide in tRNASers. Perhaps because of this, SerRS is one of the very few synthetases that does not specifically recognize the anticodon. Secondly, with the exception of mammalian mitochondria, all tRNASers are class 2 tRNAs, that is they possess a long variable arm. This feature is the major identity element of tRNASer and SerRS has acquired a unique feature to recognize it, an N-terminal coiled-coil domain. Exactly how the highly unusual mammalian mitochondria tRNASers are recognized by mitochondrial seryl-tRNA synthetase is still unclear. Thirdly, the majority of organisms require co-translational incorporation of seleno-cysteine (Sec) into a few critical seleno-proteins. This is achieved by SerRS firstly charging a specialized and unique suppressor tRNA, tRNASec with serine and subsequently enzymatic conversion of Ser-tRNASec to Sec-tRNASec. The latter species can be used to incorporate seleno-cysteine at stop codons in seleno-proteins by means of a special mechanism that depends on the codon context. Fourthly, although in general SerRSs are universally rather well conserved enzymes, it has recently been discovered that a form with a markedly diverged primary sequence exists in a limited group of archeabacteria. The reason for this is still obscure. In this chapter we review what is known about SerRS structure and function and the co-evolution of SerRS and tRNASer and their mode of recognition in different organisms.

tRNASer, seryl-tRNA synthetase

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