Structure of the yeast tRNA m7G methylation complex

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Genetics

Background:

• The N7-methylguanosine (m7G) modification on tRNA plays a role in regulating tRNA stability and is linked to rapid tRNA degradation pathways.
• In yeast, the Trm8-Trm82 complex is responsible for catalyzing this essential m7G modification.

Purpose of the Study:

• To elucidate the structural basis of the Trm8-Trm82 complex's function in m7G modification.
• To understand the role of the Trm82 subunit in Trm8 activity and tRNA binding specificity.

Main Methods:

• X-ray crystallography was used to determine the structures of Trm8 alone and in complex with Trm82.
• Cocrystallization with S-adenosyl-methionine provided insights into the catalytic site.
• Small-angle X-ray scattering (SAXS) was employed to study the Trm8-Trm82-tRNA(Phe) ternary complex in solution.

Main Results:

• The crystal structure of Trm8 alone and Trm8-Trm82 complex revealed subtle conformational changes in Trm8 upon Trm82 binding, explaining Trm82's essential role.
• The catalytic site and guanine binding pocket of Trm8 were identified through cocrystallization with the methyl donor.
• A low-resolution structure of the ternary complex was proposed, outlining the tRNA binding mode and specificity determinants of the Trm8-Trm82 complex.

Conclusions:

• Trm82 is essential for the catalytic activity of Trm8 through conformational modulation.
• The structural data provide a molecular basis for understanding m7G modification and tRNA recognition.
• These findings contribute to comprehending tRNA quality control mechanisms and potential therapeutic targets.