Structure of an ancient TsaD-TsaC-SUA5-TcdA modular enzyme (TsaN)

Experimental Data Snapshot

  • Resolution: 3.21 Å
  • Aggregation State: PARTICLE 
  • Reconstruction Method: SINGLE PARTICLE 

Starting Models: experimental
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Structure-function analysis of an ancient TsaD-TsaC-SUA5-TcdA modular enzyme reveals a prototype of tRNA t6A and ct6A synthetases.

Jin, M.Zhang, Z.Yu, Z.Chen, W.Wang, X.Lei, D.Zhang, W.

(2023) Nucleic Acids Res 51: 8711-8729

  • DOI: https://doi.org/10.1093/nar/gkad587
  • Primary Citation of Related Structures:  

  • PubMed Abstract: 

    N 6-threonylcarbamoyladenosine (t6A) is a post-transcriptional modification found uniquely at position 37 of tRNAs that decipher ANN-codons in the three domains of life. tRNA t6A plays a pivotal role in promoting translational fidelity and maintaining protein homeostasis. The biosynthesis of tRNA t6A requires members from two evolutionarily conserved protein families TsaC/Sua5 and TsaD/Kae1/Qri7, and a varying number of auxiliary proteins. Furthermore, tRNA t6A is modified into a cyclic hydantoin form of t6A (ct6A) by TcdA in bacteria. In this work, we have identified a TsaD-TsaC-SUA5-TcdA modular protein (TsaN) from Pandoraviruses and determined a 3.2 Å resolution cryo-EM structure of P. salinus TsaN. The four domains of TsaN share strong structural similarities with TsaD/Kae1/Qri7 proteins, TsaC/Sua5 proteins, and Escherichia coli TcdA. TsaN catalyzes the formation of threonylcarbamoyladenylate (TC-AMP) using L-threonine, HCO3- and ATP, but does not participate further in tRNA t6A biosynthesis. We report for the first time that TsaN catalyzes a tRNA-independent threonylcarbamoyl modification of adenosine phosphates, leading to t6ADP and t6ATP. Moreover, TsaN is also active in catalyzing tRNA-independent conversion of t6A nucleoside to ct6A. Our results imply that TsaN from Pandoraviruses might be a prototype of the tRNA t6A- and ct6A-modifying enzymes in some cellular organisms.

  • Organizational Affiliation

    School of Life Sciences, Key Laboratory of Cell Activities and Stress Adaptation of the Ministry of Education, Lanzhou University, Lanzhou 730000, China.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
N(6)-L-threonylcarbamoyladenine synthase
A, B
1,008Pandoravirus salinusMutation(s): 0 
Gene Names: psal_cds_1280
Find proteins for A0A291ATS8 (Pandoravirus salinus)
Explore A0A291ATS8 
Go to UniProtKB:  A0A291ATS8
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupA0A291ATS8
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 1 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
MN (Subject of Investigation/LOI)
Query on MN

Download Ideal Coordinates CCD File 
Experimental Data & Validation

Experimental Data

  • Resolution: 3.21 Å
  • Aggregation State: PARTICLE 
  • Reconstruction Method: SINGLE PARTICLE 
EM Software:
TaskSoftware PackageVersion

Structure Validation

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Entry History & Funding Information

Deposition Data

Funding OrganizationLocationGrant Number
National Natural Science Foundation of China (NSFC)China32000847
National Natural Science Foundation of China (NSFC)China32171300
Other government20JR10RA618
Other governmentlzujbky-2021-ct05
Other government2022021zr46

Revision History  (Full details and data files)

  • Version 1.0: 2023-07-26
    Type: Initial release
  • Version 1.1: 2023-09-20
    Changes: Data collection, Database references