Nodavirus protein A's interdomain elbow controls RNA replication organelle formation and function

Area of Science:

• Virology
• Molecular Biology
• Structural Biology

Background:

• Positive-strand RNA [(+)RNA] viruses utilize membrane-associated replication organelles (ROs) for genome replication.
• The precise mechanisms of RO formation and function remain poorly understood.

Purpose of the Study:

• To elucidate the structural and functional role of viral protein A in (+)RNA virus replication.
• To identify key regulatory elements within protein A that control RO assembly and activity.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structure of nodaviral replication organelles.
• Extensive mutational analyses and genetic complementation assays were performed on protein A.

Main Results:

• A 17-amino acid "elbow" segment of protein A was identified as a critical regulator of RO formation.
• Distinct subsegments of the elbow coordinate proto-crown assembly and activate RNA capping and polymerase domains.
• RNA capping activity was localized to the crown floor, formed by the proto-crown.

Conclusions:

• The protein A elbow acts as a master regulator, controlling RO assembly and licensing key enzymatic activities.
• Understanding these regulatory mechanisms provides insights into (+)RNA virus replication strategies.
• This work lays the foundation for developing novel antiviral control strategies.