2mx1 | pdb_00002mx1
Structure of the E. coli Threonylcarbamoyl-AMP Synthase TSAC
Structural highlights
FunctionTSAC_ECOLI Required for the formation of a threonylcarbamoyl group on adenosine at position 37 (t(6)A37) in tRNAs that read codons beginning with adenine. Catalyzes the conversion of L-threonine, bicarbonate/CO(2) and ATP to give threonylcarbamoyl-AMP (TC-AMP) as the acyladenylate intermediate, with the release of pyrophosphate. Is also able to catalyze the reverse reaction in vitro, i.e. the formation of ATP from TC-AMP and PPi. Shows higher affinity for the full-length tRNA(Thr) lacking only the t(6)A37 modification than for its fully modified counterpart. Could also be required for the maturation of 16S rRNA. Binds to double-stranded RNA but does not interact tightly with either of the ribosomal subunits, or the 70S particles.[HAMAP-Rule:MF_01852][1] [2] [3] [4] [5] Publication Abstract from PubMedThe hypermodified nucleoside N6-threonylcarbamoyladenosine (t6A37) is present in many distinct tRNA species and has been found in organisms in all domains of life. This post-transcriptional modification enhances translation fidelity by stabilizing the anticodon-codon interaction in the ribosomal decoding site. The biosynthetic pathway of t6A37 is complex and not well understood. In bacteria, four proteins have been discovered to be both required and sufficient for t6A37 modification: TsaC, TsaD, TsaB and TsaE. Of these, TsaC and TsaD are members of universally conserved protein families. Although TsaC has been shown to catalyze the formation of L-threonylcarbamoyl-AMP (TC-AMP), a key intermediate in the biosynthesis of t6A37, the details of the enzymatic mechanism remain unsolved. Therefore, the solution structure of Escherichia coli TsaC was characterized by NMR in order to further study the interactions with ATP and L-threonine, both substrates of TsaC in the biosynthesis of TC-AMP. Several conserved amino acids were identified that create a hydrophobic binding pocket for the adenine of ATP. Additionally, two residues were found to interact with L-threonine. Both binding sites are located in a deep cavity at the center of the protein. Models derived from the NMR data and molecular modeling reveal several sites with considerable conformational flexibility in TsaC that may be important for L-threonine recognition, ATP activation and/or protein-protein interactions. These observations further the understanding of the enzymatic reaction catalyzed by TsaC, a threonylcarbamoyl-AMP synthase, and provide structure-based insight into the mechanism of t6A37 biosynthesis. NMR-based structural analysis of threonylcarbamoyl-AMP synthase and its substrate interactions.,Harris KA, Bobay BG, Sarachan KL, Sims AF, Bilbille Y, Deutsch C, Iwata-Reuyl D, Agris PF J Biol Chem. 2015 Jun 9. pii: jbc.M114.631242. PMID:26060251[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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