A freestanding proofreading domain is required for protein synthesis quality control in Archaea.
Threonyl-tRNA synthetase (ThrRS) participates in protein synthesis quality control by selectively editing the misacylated species Ser-tRNA(Thr). In bacteria and eukaryotes the editing function of ThrRS resides in a highly conserved N-terminal domain distant from the active site. Most archaeal ThrRS proteins are devoid of this editing domain, suggesting evolutionary divergence of quality-control mechanisms. Here we show that archaeal editing of Ser-tRNAThr is catalyzed by a domain unrelated to, and absent from, bacterial and eukaryotic ThrRSs. Despite the lack of sequence homology, the archaeal and bacterial editing domains are both reliant on a pair of essential histidine residues suggestive of a common catalytic mechanism. Whereas the archaeal editing module is most commonly part of full-length ThrRS, several crenarchaeal species contain individual genes encoding the catalytic (ThrRS-cat) and editing domains (ThrRS-ed). Sulfolobus solfataricus ThrRS-cat was shown to synthesize both Thr-tRNAThr and Ser-tRNAThr and to lack editing activity against Ser-tRNAThr. In contrast, ThrRS-ed lacks aminoacylation activity but can act as an autonomous protein in trans to hydrolyze specifically Ser-tRNAThr, or it can be fused to ThrRS-cat to provide the same function in cis. Deletion analyses indicate that ThrRS-ed is dispensable for growth of S. solfataricus under standard conditions but is required for normal growth in media with elevated serine levels. The growth phenotype of the ThrRS-ed deletion strain suggests that retention of the discontinuous ThrRS quaternary structure relates to specific physiological requirements still evident in certain Archaea.
Korencic
Dragana
D
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA.
Ahel
Ivan
I
Schelert
James
J
Sacher
Meik
M
Ruan
Benfang
B
Stathopoulos
Constantinos
C
Blum
Paul
P
Ibba
Michael
M
Söll
Dieter
D
D000215:Acylation; D000595:Amino Acid Sequence; D002678:Chimera; D017353:Gene Deletion; D019848:Gene Expression Regulation, Archaeal; D006868:Hydrolysis; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D017393:RNA Editing; D012346:RNA, Transfer, Amino Acyl / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism; D016944:Sulfolobus / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D013912:Threonine / Q000378:metabolism; D013914:Threonine-tRNA Ligase / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*
D012346:RNA, Transfer, Amino Acyl; D013912:Threonine; D012694:Serine; D013914:Threonine-tRNA Ligase