Ribosomal RNA methylation by GidB modulates discrimination of mischarged tRNA

Area of Science:

• Molecular Biology
• Microbiology
• Structural Biology

Background:

• Cellular protein synthesis pathways aim to minimize translational errors.
• Ribosomal decoding centers are generally considered unable to detect mischarged tRNAs.
• The methyltransferase GidB modifies 16S ribosomal RNA in mycobacteria.

Purpose of the Study:

• To investigate the role of GidB in translational fidelity in mycobacteria.
• To elucidate the mechanism by which mycobacterial ribosomes discriminate mischarged tRNAs.
• To understand the structural basis of GidB-mediated translational error prevention.

Main Methods:

• Genetic deletion of the *gidB* gene in *Mycobacterium smegmatis*.
• Analysis of mistranslation rates in wild-type and *gidB*-deleted strains.
• Cryo-electron microscopy (cryo-EM) to determine ribosomal structures.

Main Results:

• Deletion of *gidB* increased ribosomal discrimination against mischarged tRNAs, particularly in strains with high mistranslation rates.
• GidB deletion was necessary but not sufficient to reduce misacylation-driven mistranslation.
• Cryo-EM structures revealed a GidB-dependent interaction between methylated 16S rRNA and ribosomal protein S12, potentially influencing translational fidelity.

Conclusions:

• Mycobacterial ribosomes possess a GidB-dependent mechanism to discriminate mischarged tRNAs.
• 16S rRNA methylation by GidB plays a crucial role in preventing widespread translational errors.
• This finding reveals a novel layer of quality control in bacterial protein synthesis.