Cryo-EM structure of the Rous sarcoma virus octameric cleaved synaptic complex intasome

Area of Science:

• Virology
• Structural Biology
• Molecular Biology

Background:

• Retroviral intasomes, complexes of integrase (IN) and viral DNA, exhibit structural diversity despite conserved integration mechanisms.
• Understanding intasome assembly is crucial for deciphering retroviral replication strategies.

Purpose of the Study:

• To investigate the assembly mechanisms of Rous sarcoma virus (RSV) intasomes.
• To determine the structure of the RSV octameric intasome and identify key conformational changes during assembly.

Main Methods:

• Single particle cryo-electron microscopy was used to determine the structure of the RSV octameric intasome.
• In vitro assays and infectivity studies were performed using site-directed mutagenesis of IN C-terminal domain.

Main Results:

• The structure of the RSV octameric intasome revealed flexibility in distal IN dimers and movement within the intasome core, suggesting ordered conformational transitions.
• Amino acid substitutions in the IN C-terminal domain impacted intasome assembly, function, and viral infectivity.
• Unexpectedly, the 17 C-terminal amino acids of IN were dispensable for infection, though they regulated tetrameric to octameric intasome transitions in vitro.

Conclusions:

• RSV intasome assembly involves ordered conformational transitions, with flexible distal IN dimers potentially playing a role in target DNA capture.
• The C-terminal domain of RSV IN has a complex role in intasome maturation and viral infectivity, with a dispensable region for infection identified.