Can a signal sequence become too hydrophobic?

Area of Science:

• Virology
• Molecular Biology
• Protein Trafficking

Background:

• The signal sequence directs proteins to their cellular destinations.
• Understanding signal sequence function is crucial for protein export and viral replication.

Purpose of the Study:

• To investigate the role of the N-terminal hydrophilic domain of the pseudorabies virus glycoprotein gC signal sequence in protein export.
• To determine the impact of charge and hydrophobicity alterations within this domain on gC translocation and export.

Main Methods:

• Characterization of pseudorabies virus glycoprotein gC mutants with specific alterations in the signal sequence's N region.
• Analysis of membrane translocation and export efficiency of the modified gC protein in infected cells.

Main Results:

• Basic residues in the N region are not essential for gC export.
• A net negative charge in the N region caused a slight impairment in membrane translocation.
• A significant export defect was observed only with a net negative charge or increased hydrophobicity.
• A specific mutation (leucine for arginine) led to a substantial export defect due to increased hydrophobicity, which could be corrected by reducing hydrophobicity.

Conclusions:

• The N region's charge influences gC export, with a net negative charge being detrimental.
• An upper limit for hydrophobicity in eukaryotic signal sequences may exist, beyond which export is impaired.
• Findings provide insights into signal sequence design and protein export mechanisms.