engleski

Two types of seryl-tRNA synthetase in methanogenic archaea

Methanogenic archaea are a polyphyletic group of methanogen producing archaea that can be divided into two classes: class I and class II. Methanogens employ two types of seryl-tRNA synthetase (SerRS), an enzyme essential for protein synthesis. Canonical (bacterial-type) SerRS occurs in majority of organisms including methanogens, while a highly diverged, structurally atypical, methanogenic-type SerRS is confined only to methanogenic archaea. Interestingly, both types of SerRS are equally distributed in class I and class II. The phylogenetic distribution of methanogenic-type SerRS coincides with the phylogenetic distribution of core methanogenesis enzymes, implying that metSerRS is endogenous in methanogens. Bacterial-type SerRS seems to be horizontally transferred from bacteria, archaea or eukaryotes. Since archaeon Methanosarcina barkeri contains both types of SerRS, which were structurally and functionally well characterized in our laboratory, we set out to develop an in vivo system in E. coli for studying archaeal tRNA serylation by both enzymes. We show that co-expression of M. barkeri SerRS gene, encoding bacterial- or methanogenic-type SerRS (mMbSerRS), with the gene for archaeal suppressor tRNA(CGA) leads to suppression of bacterial amber mutations. The efficiency of suppression by mMbSerRS variants faithfully reflects enzymes' serylation propensity obtained by in vitro kinetic measurements, confirming the importance of idiosyncratic structural features.

seryl-tRNA synthetase; methanogenic archaea; evolution

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