9WGB

Cryo-EM structure of I3L-ssDNA double-ring complex

Summary for 9WGB

• Entry DOI: 10.2210/pdb9wgb/pdb
• EMDB information: 65952
• Descriptor: Protein OPG079 (1 entity in total)
• Functional Keywords: ssdna-binding, dna replication, double-ring complex, ob-like, viral protein
• Biological source: Monkeypox virus Zaire-96-I-16
• Total number of polymer chains: 16
• Total formula weight: 406607.34

Authors

Ma, J.,Yang, K. (deposition date: 2025-08-23, release date: 2026-06-17, Last modification date: 2026-08-19)

Primary citation

Yang, K.,Ge, M.,Song, J.,Zou, J.,Zhang, Y.,Wu, H.,Wang, Y.,Ma, J.
Double-ring assembly of mpox virus I3L reveals an unconventional mechanism for ssDNA engagement.
Cell Rep, 45:117659-117659, 2026

PubMed Abstract: Poxviruses, including variola and mpox virus (MPXV), are large dsDNA viruses that replicate their genomes in the host cytoplasm via virally encoded proteins. The single-stranded DNA-binding protein (SSB) I3L is an essential component of this replication machinery, yet its structural mechanism remains to be fully elucidated. Here, we determined the cryo-EM structure of MPXV I3L and constructed a structural model of its complex with ssDNA. Unlike canonical SSBs, I3L forms an architectural double-ring assembly. The individual I3L protomer adopts an OB-fold variant with specialized elements beyond the classic pattern. Furthermore, biochemical assays and structural modeling suggest an assembly-dependent ssDNA-engagement mode, while monomeric binding features remain conserved. These distinctive structural features suggest a specialized molecular mechanism for poxviral DNA replication. Our findings advance the mechanistic understanding of poxvirus genome maintenance and provide perspectives for antiviral development against MPXV.

PubMed: 42418326
DOI: 10.1016/j.celrep.2026.117659

Experimental method

ELECTRON MICROSCOPY (3.6 Å)