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The paramyxovirus fusion protein C-terminal region: mutagenesis indicates an indivisible protein unit

Aarohi Zokarkar1, Robert A Lamb

  • 1Department of Molecular Biosciences, Northwestern University, Evanston, Illinois, USA.

Journal of Virology
|December 16, 2011
PubMed

Insights

The C terminus of the paramyxovirus fusion (F) protein is specific to its ectodomain for effective cell fusion. Introducing destabilizing mutations or native sequences partially restored fusion, indicating a structure-specific interaction.

Area of Science:

  • Virology
  • Molecular Biology
  • Cell Biology

Background:

  • Paramyxoviruses initiate host cell entry via viral envelope and host cell membrane fusion.
  • This fusion process is orchestrated by the viral fusion (F) protein, which undergoes significant conformational changes.
  • The C terminus of the parainfluenza virus 5 F protein comprises a membrane-proximal external region (MPER), transmembrane domain, and cytoplasmic tail.

Purpose of the Study:

  • To investigate the sequence-specific requirements of the F protein's C terminus for mediating viral fusion.
  • To determine if heterologous C-terminal regions from other paramyxoviruses can functionally interact with the PIV5 F ectodomain.

Main Methods:

  • Construction of chimeric F proteins combining the PIV5 F ectodomain with C-terminal regions (MPER, TM, cytoplasmic tail) from various paramyxoviruses.
  • Analysis of chimeric protein expression at the cell surface.
  • Assessment of the cell-cell fusion capabilities mediated by the chimeric F proteins.
  • Introduction of destabilizing mutations (e.g., S443P) and native PIV5 F sequences into chimeric constructs.
  • Alanine scanning mutagenesis of the MPER to elucidate its regulatory role in fusion.

Main Results:

  • Chimeric F proteins with heterologous C termini generally failed to induce cell fusion, despite variable surface expression.
  • Fusion activity was partially restored by introducing a destabilizing mutation (S443P) or by replacing specific regions with native PIV5 F sequences.
  • Restoration of fusion was not additive, suggesting a requirement for specific structural compatibility between the ectodomain and C terminus.
  • Alanine scanning mutagenesis of the MPER revealed both hyperfusogenic and hypofusogenic mutations, highlighting its regulatory function.

Conclusions:

  • The C terminus of the paramyxovirus F protein likely forms a specific structure that is functionally dependent on its cognate ectodomain.
  • The MPER region plays a critical regulatory role in the fusion process.
  • Understanding these specific interactions is crucial for deciphering the molecular mechanisms of paramyxovirus entry.

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