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

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.