Genetics and Functions of Herpes Simplex Virus Type 1 Membrane Proteins in Virus-Induced Cell Fusion, Virion Morphogenesis and Egress
The Herpes Simplex Virus life cycle contains a number of membrane fusion events that must function properly to ensure a productive infection, including: virus attachment and entry into susceptible cells, de-envelopment at the outer nuclear lamellae, and virus-induced cell-to-cell fusion. A virus-free cell fusion assay was recently developed in order to attempt to understand the underlying mechanisms that are responsible for viral fusion events and was utilized in order to investigate the effect of mutations targeted to the carboxyl terminus of gB. We showed that the predicted alpha helical domain H17b within the carboxyl-terminus of gB is involved in both virus-induced and virus-free fusion systems, and heparin was shown to be a specific inhibitor of gB-mediated fusion in both systems, while resistance to heparin inhibition of gB-mediated cell fusion was associated with the predicted alpha helical structure H17b. An important difference between virus-free and virus-induced membrane fusion is that virus-expressed gB mediates an insignificant amount of cell-to-cell fusion, while transiently expressed gB causes extensive cell-to-cell fusion. gK was recently shown to inhibit cell fusion resulting from transiently expressed gB, gD, gH and gL and hypothesized to function as a negative regulator of membrane fusion. However, we show that gK can not solely act as a negative regulator of gB-mediated membrane fusion, since gK is demonstrated to be absolutely required for virus-induced cell fusion to occur, suggesting a more complicated relationship between gK and gB. A recent publication from our laboratory showed that syncytial mutations in either gB or gK failed to cause fusion in the absence of the UL20 gene, suggesting that the UL20 protein was essential for virus-induced cell fusion. Absence of the UL20 gene also caused accumulation of unenveloped capsids into the cytoplasm, indicating that UL20p functioned in cytoplasmic stages of virion envelopment. We delineated via site-directed mutagenesis the functional domains of UL20p involved in infectious virus production and virus-induced cell fusion, revealing that the role of UL20p in virus-induced cell fusion can be functionally separated from its role in cytoplasmic virion morphogenesis.
Advisor:Konstantin G. Kousoulas; John C. Larkin; John E. Chandler; Thomas R. Klei; Patrick J. DiMario
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Keywords:veterinary microbiology parasitology medical sciences
Date of Publication:11/04/2004