Organyl 5'-Phosphates in siRNA Guide Strands: Structure-Function Relationships Governing Anchoring in Argonaute 2 and...

Area of Science:

• Biochemistry
• Molecular Biology
• Chemical Biology

Background:

• Efficient RNA interference (RNAi) relies on guide strand loading into Argonaute2 (AGO2), requiring a 5'-phosphate (5'-P).
• The 5'-P is metabolically unstable in vivo, limiting RNAi efficacy.
• Structural understanding of 5'-P mimics interacting with AGO2 and degradative enzymes is incomplete.

Purpose of the Study:

• To systematically synthesize and characterize novel organyl 5'-phosphate (5'-POR) mimics.
• To investigate the structural basis for AGO2 interaction and resistance to enzymatic degradation.
• To expand the chemical space of 5'-P mimics for improved RNAi therapeutics.

Main Methods:

• Synthesis and characterization of a diverse panel of 35 organyl 5'-phosphate derivatives (5'-POR).
• Assessment of AGO2 compatibility in cellular assays.
• Evaluation of resistance to phosphatase and 5'-exonuclease degradation.
• X-ray crystallography of a 5'-PO-PhPrp guide strand within AGO2.

Main Results:

• Methyl (Me) and phenylpropargyl (PhPrp) substituted 5'-POR mimics are well-tolerated by AGO2.
• 5'-phosphorothioate (5'-PS) and 5'-mesylphosphoramidate (5'-MsPA) also show AGO2 compatibility.
• All tested mimics resist phosphatase degradation; 5'-POR and 5'-PS-PhPrp resist 5'-exonuclease.
• Crystal structure reveals π-π interactions between PhPrp and the AGO2 MID domain hydrophobic pocket.

Conclusions:

• Organyl 5'-phosphate mimics offer enhanced metabolic stability for guide strands.
• These mimics improve AGO2 anchoring through novel hydrophobic and π-π interactions.
• Findings provide new strategies for developing more effective RNAi-based therapies.