Insights into herpes simplex virus type 1 assembly: Membrane association and intracellular trafficking of the VP22 tegument protein

In an effort to identify how HSV-1 tegument proteins localize to the cellular site of final envelopment, we have initiated studies on the intracellular trafficking properties of the VP22 tegument protein. VP22 was selected as the keystone to these investigations because it represents one of the most abundant tegument proteins with nearly 2,000 copies present within each virion. Despite its abundance, the role of VP22 during viral infection remains elusive. Expression of VP22 in either the presence or absence of HSV-1 infection results in its localization to acidic compartments of the cell that include the TGN, the putative site of HSV-1 final envelopment. In addition, localization of VP22 to the TGN suggests that VP22 is membrane associated. Membrane pelleting and membrane flotation assays confirmed that VP22 partitions with the cellular membrane fraction. However, VP22 can be extracted from membranes in the presence of a high concentration of salt, implicating an electrostatic basis for the association of VP22 with membranes. Furthermore, extensive truncation mutagenesis revealed that the association of VP22 with membranes is a property attributable to amino acids 120--225 of this 301-amino-acid protein. Collectively, these results demonstrate that VP22 contains specific information required for targeting to membranes of the acidic compartments of the cell including the TGN, suggesting a potential role for VP22 during tegumentation and/or final envelopment.; Collectively, the studies described within this dissertation advance our understanding of the role of VP22 during HSV-1 assembly. Analysis of VP22 has provided novel insights into HSV-1 assembly, which will serve as a foundation for future examination of intracellular trafficking properties and interactions among tegument and envelope proteins that may cooperatively promote the budding process at the TGN. (Abstract shortened by UMI.)...