How glutaminyl-tRNA synthetase selects glutamine

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Aminoacyl-tRNA synthetases (aaRS) are crucial enzymes ensuring protein synthesis fidelity.
• Glutaminyl-tRNA synthetase (GlnRS) exhibits a unique mechanism requiring tRNA binding prior to amino acid activation.
• Understanding GlnRS substrate specificity necessitates structural analysis of the enzyme with both tRNA and amino acid substrates.

Purpose of the Study:

• To elucidate the molecular basis of amino acid recognition by GlnRS.
• To determine the structural interactions governing glutamine binding and activation.
• To investigate the role of tRNA binding in GlnRS substrate specificity.

Main Methods:

• Synthesis of a stable glutaminyl-adenylate analog inhibitor.
• Cocrystallization of GlnRS, tRNA2Gln, and the glutaminyl-adenylate analog.
• Refinement of the ternary complex crystal structure at 2.4 Å resolution.

Main Results:

• A stable glutaminyl-adenylate analog was synthesized and shown to inhibit GlnRS.
• The crystal structure of the ternary complex (GlnRS-tRNA2Gln-glutaminyl-adenylate analog) was determined.
• Key interactions between glutamine and the GlnRS binding site were identified.

Conclusions:

• GlnRS distinguishes glutamine from glutamic acid by recognizing both hydrogen atoms on the glutamine sidechain nitrogen.
• Tyrosine 211 (Tyr211) and a water molecule, acting as hydrogen-bond acceptors, are critical for this specific recognition.
• tRNA binding, potentially via the terminal nucleotide A76, influences the orientation of Tyr211, facilitating amino acid activation.