Envelope polypeptides of Friend leukemia virus: purification and structural analysis

Area of Science:

• Virology
• Molecular Biology
• Protein Chemistry

Background:

• Surface glycoproteins of Friend murine leukemia virus (FMLV) are crucial for viral structure and function.
• Understanding the interactions between viral glycoproteins and membrane polypeptides is key to deciphering viral assembly and infectivity.

Purpose of the Study:

• To investigate the nature of the association between FMLV surface glycoproteins (gp69/71) and membrane polypeptides (p12(E)/15(E)).
• To characterize the structural components and assembly of FMLV surface projections.

Main Methods:

• Solubilization of viral membranes with Triton X-100.
• Velocity sedimentation to isolate glycoprotein-polypeptide aggregates (rosettes).
• Gel chromatography after disulfide bond reduction for purification.
• Peptide mapping and two-dimensional polyacrylamide gel electrophoresis for structural analysis.

Main Results:

• Approximately 90% of FMLV surface glycoproteins are noncovalently associated with membrane polypeptides; 10% are linked by disulfide bridges.
• Heterodimers (gp84/86) were identified, composed of gp71/gp69 and p15(E)/p12(E).
• Specific associations were elucidated: gp86 consists of gp71 with p15(E) and p12(E), while gp84 comprises gp69 bound to p12(E).
• Isolated heterodimers could reassociate to form structures resembling native viral knobs.

Conclusions:

• FMLV surface glycoproteins and membrane polypeptides interact through both noncovalent and disulfide-linked associations.
• The identified heterodimers (gp84/86) are key structural units of the viral envelope.
• Structural analysis reveals specific protein-protein interactions critical for FMLV surface morphology.