A modified dinucleotide motif specifies tRNA recognition by TLR7

Area of Science:

• Immunology
• Molecular Biology
• RNA Biology

Background:

• RNA acts as a pathogen-associated molecular pattern (PAMP), signaling microbial infection to the innate immune system.
• Toll-like receptor 7 (TLR7) distinguishes self from nonself RNA based on modification patterns, with ribose methylation at guanosine 18 typically inhibiting immune responses.
• Previous understanding focused on single nucleotide modifications in RNA recognition by TLR7.

Discussion:

• This study reveals that TLR7 recognition of RNA is dictated by methylated dinucleotides, extending beyond single modifications.
• The optimal motif for immune recognition involves two purines, whereas pyrimidines reduce the impact of ribose methylation.
• These findings suggest that the orientation of RNA during TLR7 interaction is not fixed, implying a processive inspection mechanism.

Key Insights:

• TLR7 recognizes specific methylated dinucleotide motifs within RNA.
• The sequence context (purine-rich) enhances the immune recognition of these methylated dinucleotides.
• RNA modification patterns, specifically methylated dinucleotides, are critical for self/nonself discrimination by TLR7.

Outlook:

• Further investigation into the structural basis of TLR7's processive inspection of RNA.
• Exploring the therapeutic potential of targeting specific RNA motifs for immune modulation.
• Understanding the role of other RNA modifications in innate immune recognition.