Reevaluating herpes simplex virus hemifusion.

Area of Science:

• Virology
• Molecular Biology
• Cell Biology

Background:

• Enveloped viruses utilize viral fusion proteins for membrane fusion, often proceeding through a hemifusion intermediate.
• Herpes simplex virus type 1 (HSV-1) entry requires glycoproteins D (gD), B (gB), and the heterodimer of glycoprotein H and L (gH/gL).
• The precise role of HSV-1 gH/gL in viral fusion has been debated, with some evidence suggesting it acts as a fusion protein.

Purpose of the Study:

• To investigate the functional role of HSV-1 glycoproteins, particularly gH/gL, in the process of viral membrane fusion.
• To determine if gH/gL alone can mediate hemifusion or if other viral glycoproteins are required.

Main Methods:

• Utilized cell-cell and virus-cell based hemifusion assays to assess lipid mixing.
• Employed glycosylphosphatidylinositol (GPI)-linked hemagglutinin (HA) as a positive control for hemifusion detection.
• Analyzed a mutant gH protein (824L gH) with a cytoplasmic tail insertion to evaluate its fusion capabilities.

Main Results:

• All tested HSV-1 entry glycoproteins (gD, gB, and gH/gL) were necessary for observing lipid mixing in hemifusion assays.
• The 824L gH mutant was deficient in mediating hemifusion, despite normal cell surface expression.
• The results indicate that gH/gL does not function independently as a fusion protein.

Conclusions:

• HSV-1 membrane fusion requires the coordinated action of all four entry glycoproteins, gD, gB, and gH/gL.
• The gH/gL complex's role in fusion is not that of an independent fusion protein.
• The gH 824L mutation impairs gH/gL function at a stage preceding HSV-induced lipid mixing.