Summary information and primary citation
- PDB-id
-
13fn;
DSSR-derived features in text and
JSON formats; DNAproDB
- Class
- RNA binding protein-RNA
- Method
- cryo-EM (3.2 Å)
- Summary
- Thermotoga maritima threonylcarbamoyl transfer complex
(tsab2d) in complex with escherichia coli trna(thr)
- Reference
-
Kutchuashvili A, Scheleen E, Guynes G, Wu J, Chan CK,
Dedon P, Iwata-Reuyl D, Swairjo MA (2026): "Anticodon
loop remodeling and D-stem shape drive the specific
recognition of ANN-decoding tRNAs for t6A
modification." Nucleic Acids Res.,
54. doi: 10.1093/nar/gkag599.
- Abstract
- N6-threonylcarbamoyladenosine (t6A) is a universal
transfer RNA (tRNA) modification essential for
translational fidelity. The modification is installed at
position 37 of ANN-decoding tRNAs (N is A, U, G, or C) by
transfer of a threonylcarbamoyl moiety from a pathway
intermediate, catalyzed in bacteria by the TsaBD complex.
Despite the strict requirement for the 36-UAA-38 sequence
in substrate tRNAs, the structural basis for this
specificity has remained unclear. We determined cryo-EM
structures of the Thermotoga maritima t6A synthase bound to
unmodified and to natively modified tRNA carrying the t6A37
modification, at a nominal resolution of 3.2 Å. In both
structures, A37 is positioned in the active site, and the
anticodon loop is remodeled into a zig-zag conformation not
previously observed in tRNA, stabilized by conserved
interactions with the RNA backbone at the TsaD/TsaB
interface. The wobble and middle anticodon bases occupy
shallow surface pockets without base-specific contacts,
explaining tolerance to base identity at these positions.
In contrast, U36 and A38 are recognized indirectly through
formation of a base triple with U32. Additional D-stem
contacts provide a second mode of indirect readout.
Together with mutagenesis data, the structures reveal the
molecular basis for restriction of t6A37 to ANN-decoding
tRNAs and the requirement for A38.
