Structural insights into double-stranded RNA recognition and transport by SID-1.

Area of Science:

• Molecular Biology
• Structural Biology
• Genetics

Background:

• Cellular RNA uptake is vital for RNA interference (RNAi) and novel therapeutics.
• Systemic RNAi in C. elegans relies on SID-1 mediated double-stranded RNA (dsRNA) transport.
• The precise mechanisms of dsRNA internalization by SID-1 are not fully understood.

Purpose of the Study:

• To elucidate the structural basis of dsRNA recognition and import by SID-1.
• To investigate the role of SID-1's structural features in dsRNA internalization.
• To provide mechanistic insights for developing dsRNA-based applications.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine structures of SID-1, SID-1-dsRNA complex, and human homologs (SIDT1, SIDT2).
• Structural analysis to identify molecular determinants for dsRNA binding.
• In vivo studies involving deletion of intracellular loops to assess dsRNA uptake and RNAi efficacy.

Main Results:

• Determined high-resolution cryo-EM structures of SID-1 and its complex with dsRNA.
• Identified conserved homodimeric architecture in SID-1 homologs, with SID-1 possessing unique dsRNA recognition sites.
• Demonstrated that altering an intracellular loop in SID-1 impairs dsRNA uptake and systemic RNAi, suggesting an endocytic mechanism.

Conclusions:

• SID-1's structure explains its specific recognition and import of dsRNA.
• Structural insights into SID-1 function pave the way for enhanced RNA-based therapies.
• The findings suggest an endocytic pathway for SID-1-mediated dsRNA internalization.