Structural basis of regulated m⁷G tRNA modification by METTL1-WDR4.

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• Chemical modifications of RNA, such as N7-methylguanosine (m7G), are crucial for biological processes.
• The METTL1-WDR4 complex is responsible for m7G modification in specific tRNAs, and its dysregulation is linked to cancer and developmental disorders.
• The precise mechanism of METTL1-WDR4 tRNA modification and its regulation remains unclear.

Purpose of the Study:

• To elucidate the molecular mechanisms underlying tRNA substrate recognition by the METTL1-WDR4 complex.
• To investigate the regulatory mechanisms controlling METTL1-WDR4 methyltransferase activity.
• To understand the structural basis for METTL1-WDR4 function and its role in cellular processes.

Main Methods:

• Structural studies (e.g., X-ray crystallography, cryo-EM) of the human METTL1-WDR4 complex.
• Biochemical assays to assess methyltransferase activity and substrate binding.
• Cellular studies to investigate the functional impact of METTL1-WDR4 and its regulation.

Main Results:

• WDR4 acts as a scaffold, binding both METTL1 and the tRNA T-arm.
• Upon tRNA binding, METTL1 undergoes conformational changes, with its alpha C and alpha 6 helices stabilizing the tRNA variable loop.
• The previously presumed disordered N-terminal region of METTL1 is integral to the catalytic pocket and essential for methyltransferase activity.
• Phosphorylation at serine 27 (S27) in the METTL1 N-terminus inhibits methyltransferase activity by disrupting the catalytic center.

Conclusions:

• The study provides a detailed molecular understanding of how METTL1-WDR4 recognizes tRNA substrates.
• Phosphorylation of METTL1 at S27 is a key regulatory mechanism inhibiting methyltransferase activity.
• The N-terminal region of METTL1 is identified as a critical hub for methyltransferase activity and regulation.