Structures of Substrate Complexes of Foamy Viral Protease-Reverse Transcriptase.

Area of Science:

• Structural Biology
• Virology
• Biochemistry

Background:

• Reverse transcriptases (RTs) are essential for retroviral replication, converting RNA to DNA.
• Foamy viruses (FVs) possess a unique RT fused with a protease (PR) domain, unlike other retroviruses.
• The mechanism of nucleic acid substrate binding by FV RTs remained structurally uncharacterized.

Purpose of the Study:

• To elucidate the structural mechanism of nucleic acid substrate binding by the full-length marmoset foamy virus (MFV) protease-reverse transcriptase (PR-RT).
• To investigate the oligomeric state and substrate-binding modes of MFV PR-RT.

Main Methods:

• X-ray crystallography was employed to determine the structures of MFV PR-RT complexes with RNA/DNA hybrid and dsDNA substrates.
• Cryo-electron microscopy was used to reconstruct the architecture of the full-length MFV PR-RT-dsDNA complex.
• Biochemical data were integrated with structural findings.

Main Results:

• The crystal structure of monomeric full-length MFV PR-RT bound to an RNA/DNA hybrid substrate was determined.
• A distinct structure of MFV PR-RT with an RNase H deletion bound to dsDNA revealed an asymmetric homodimer.
• Cryo-EM confirmed the dimeric architecture of the MFV PR-RT-dsDNA complex.

Conclusions:

• This study provides the first structural insights into nucleic acid binding by a foamy viral RT.
• MFV PR-RT exhibits plasticity in its oligomeric state, existing as a monomer with RNA/DNA hybrids and a dimer with dsDNA.
• These findings reveal a unique substrate-binding mechanism and oligomerization adaptability in foamy viral RTs.