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Generation and Assembly of Virus-Specific Nucleocapsids of the Respiratory Syncytial Virus
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Structures of nucleotide-bound Redondovirus Rep protein link conformation and function
Saira Montermoso1,2, Kushol Gupta2, Ruth Anne Pumroy3
1Graduate Group in Biochemistry and Molecular Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
Plos Pathogens
|March 4, 2026
Summary
Researchers visualized the structures of a Redondovirus Rep protein, revealing how it functions in viral DNA replication. The study highlights a unique staircase arrangement in the ADP-bound state, crucial for helicase activity in circular DNA viruses.
Area of Science:
- Structural Biology
- Virology
- Biochemistry
Background:
- Circular Rep-encoding single-stranded DNA (CRESS-DNA) viruses utilize Rep proteins for replication.
- Rep proteins possess nicking endonuclease and NTP-dependent helicase activities.
- Redondoviridae is a newly identified family of human-associated CRESS-DNA viruses.
Purpose of the Study:
- To determine the structures of a Redondovirus Rep protein.
- To elucidate the mechanism of Rep protein function in viral DNA replication.
- To investigate the oligomeric states and functional implications of Rep protein assemblies.
Main Methods:
- Cryo-electron microscopy (cryo-EM) was used to characterize Rep protein structures.
- Biophysical analyses were employed to study Rep oligomerization.
- Structural determination of hexameric and dodecameric Rep states bound to ATPγS and ADP.
Main Results:
- The hexameric structures of Redondovirus Rep bound to ATPγS and ADP were determined.
- The ADP-bound Rep exhibited a staircase arrangement of DNA-binding loops, essential for SF3 helicase function.
- A head-to-tail dodecameric structure of ATPγS-bound Rep revealed ordered helicase and endonuclease domains.
- Conserved residues suggest the dodecameric assembly is functionally relevant across CRESS-DNA viruses.
Conclusions:
- Structural insights into Redondovirus Rep provide a mechanistic understanding of CRESS-DNA virus replication.
- The identified Rep oligomeric states and structural features offer new perspectives on viral DNA replication strategies.
- This study lays the groundwork for understanding the broader functional roles of Rep proteins in CRESS-DNA viral systems.
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