Aminoacyl-tRNA synthetases (aaRSs) play an integral role in protein synthesis, functioning to attach the correct amino acid with its cognate tRNA molecule. AaRSs are known to associate into higher-order multi-aminoacyl-tRNA synthetase complexes (MSC) involved in archaeal and eukaryotic translation, although the precise biological role remains largely unknown. To gain further insights into archaeal MSCs, possible proteinprotein interactions with the atypical Methanothermobacter thermautotrophicus seryl-tRNA synthetase (MtSerRS) were investigated. Yeast two-hybrid analysis revealed arginyl-tRNA synthetase (MtArgRS) as an interacting partner of MtSerRS. Surface plasmon resonance confirmed stable complex formation, with a dissociation constant (K D ) of 250 nM. Formation of the MtSerRS⅐MtArgRS complex was further supported by the ability of GST-MtArgRS to co-purify MtSerRS and by coelution of the two enzymes during gel filtration chromatography. The MtSerRS⅐MtArgRS complex also contained tRNA Arg , consistent with the existence of a stable ribonucleoprotein complex active in aminoacylation. Steady-state kinetic analyses revealed that addition of MtArgRS to MtSerRS led to an almost 4-fold increase in the catalytic efficiency of serine attachment to tRNA, but had no effect on the activity of MtArgRS. Further, the most pronounced improvements in the aminoacylation activity of MtSerRS induced by MtArgRS were observed under conditions of elevated temperature and osmolarity. These data indicate that formation of a complex between MtSerRS and MtArgRS provides a means by which methanogenic archaea can optimize an early step in translation under a wide range of extreme environmental conditions.
Aminoacyl-tRNA synthetases (aaRSs)2 catalyze the specific coupling of amino acids with their cognate tRNAs to produce aminoacyl-tRNAs (aa-tRNAs), which serve as starting materials for the biosynthesis of proteins. Aa-tRNA synthesis occurs in two steps: amino acid activation at the expense of ATP followed by the aminoacylation of tRNA (1). Although for most aaRSs the formation of aminoacyl-AMP does not require tRNA, cognate tRNA is necessary for amino acid activation by ArgRS, GlnRS, GluRS, and LysRS1 enzymes from many organisms (2). Based on structural features of their active sites, aaRSs can be divided into two classes, which comprise 10 members each (3). In addition, an unusual form of LysRS is found in class I (2), while class II also includes the noncanonical synthetases PylRS and SepRS (4).In all three domains of life, subsets of aaRSs have been shown to associate into higher-order multi-aminoacyl-tRNA synthetase complexes (MSCs). These complexes are distinctive compared with other macromolecular protein complexes, because their components are enzymes that carry out similar catalytic reactions simultaneously, and only some aaRSs are involved (5). In eukaryotes, MSCs tend to be larger than those discovered in bacteria and archaea and also perform a wider range of functions that include both aminoacylation and noncanonical roles b...