Structural basis of mismatch recognition by a SARS-CoV-2 proofreading enzyme

Area of Science:

• Virology
• Structural Biology
• Biochemistry

Background:

• The coronavirus 3′-to-5′ exoribonuclease (ExoN), part of the nsp10-nsp14 complex, is essential for viral RNA synthesis fidelity.
• ExoN's ability to excise nucleotide analogs limits the efficacy of antiviral therapies.

Purpose of the Study:

• To elucidate the molecular mechanisms of ExoN's proofreading and nucleotide analog excision.
• To provide structural insights into the SARS-CoV-2 nsp10-nsp14 complex's interaction with RNA substrates.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structures of wild-type and mutant SARS-CoV-2 nsp10-nsp14.
• Structures were resolved at resolutions between 2.5 and 3.9 angstroms with RNA substrates containing a 3′-end mismatch.

Main Results:

• The cryo-EM structures reveal the molecular details of ExoN substrate recognition and specificity.
• Insights into the mechanism of 3′-end mismatch correction during coronavirus RNA replication were obtained.
• The structures highlight key interactions governing ExoN's function in proofreading.

Conclusions:

• Understanding ExoN's structure-function relationship is crucial for developing effective antiviral strategies.
• The findings offer a basis for the rational design of novel therapeutics targeting coronavirus replication.
• Targeting ExoN could overcome resistance to existing nucleotide analog-based antivirals.