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Structural basis for sequence-independent substrate selection by eukaryotic wobble base tRNA deaminase ADAT2/3.

Luciano G Dolce1, Aubree A Zimmer2, Laura Tengo1

  • 1EMBL Grenoble, 71 Avenue des Martyrs, 38042, Grenoble, France.

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|November 8, 2022
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Eukaryotic deaminases modify tRNA adenosine (A34) to inosine, impacting mRNA decoding. Researchers used cryo-EM to reveal how these enzymes recognize tRNA, uncovering a novel mechanism distinct from bacterial counterparts.

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Area of Science:

  • Molecular Biology
  • RNA Biology
  • Structural Biology

Background:

  • Adenosine to inosine (A-to-I) editing at tRNA wobble positions is crucial for accurate mRNA decoding.
  • Eukaryotic deaminases responsible for this modification, particularly ADAT2/3, have unclear substrate recognition mechanisms.
  • This modification significantly impacts the translation of genetic information.

Purpose of the Study:

  • To elucidate the structural basis of eukaryotic ADAT2/3 deaminase substrate recognition.
  • To understand the mechanism of tRNA binding and editing by eukaryotic deaminases.
  • To provide insights into the evolution of RNA editing and its role in shaping the genetic code.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) to determine the structure of ADAT2/3 bound to tRNA.
  • Biochemical assays to investigate enzyme-substrate interactions.
  • Structural analysis to identify key recognition motifs and mechanisms.

Main Results:

  • The cryo-EM structure reveals ADAT2/3 distorts the tRNA anticodon loop.
  • Substrate selection relies on sequence-independent contacts via flexible motifs, differing from bacterial enzymes.
  • A gating mechanism controlling substrate entry to the active site was identified.

Conclusions:

  • Eukaryotic tRNA editing by ADAT2/3 involves a unique recognition strategy.
  • This mechanism, utilizing distal flexible regions, explains how a single tRNA can decode multiple codons.
  • The findings illuminate the evolution of the genetic code and impact the eukaryotic proteome.