Dept. of Microbiology and Immunology
Oregon Health & Science University
Herpes simplex virus (HSV) latently infects a significant proportion of the human population and has been isolated in every human community. The ubiquitous nature and rapid transmission of this pathogen are intimately associated with the envelopment and egress pathways ofHSV. Recent work has suggested that alphaherpesviruses acquire their final envelope from a cytoplasmic membrane, such as the trans-Golgi network. This envelopment process is mediated by interactions between the cytoplasmic (CT) domain of viral glycoproteins and the tegument-containing nucleocapsid (NC). Although the requirements for secondary envelopment are not identical in all alphaherpesviruses, the glycoprotein gE/gi has a significant role in the envelopment of multiple family members. This raises the possibility that gE/gi may be the primary means by which the envelope is anchored onto the nucleocapsid. In addition to its role in envelopment, gE/gi also participates in the spread and pathogenesis of alphaherpesviruses in both neuronal and epithelial cells. In this dissertation I have attempted to further characterize the role of gE/gi in the secondary envelopment and cell-to-cell spread of HSV. To this end, I identified two envelope glycoproteins, gD and gE, that are necessary for the envelopment of HSV-1, indicating that these proteins function redundantly in this process. Mutants deleted for both of these proteins accumulated large numbers of nucleocapsids in the cytoplasm but mutants lacking just gE or gD acquired an envelope with only a minor decrease in efficiency. This established three facts regarding the HSV -1 secondary envelopment pathway. First, HSV acquires its final envelope from a host cell membrane in the xvii cytoplasm mediated by the glycoproteins gD and gE. Second, gD and gE share some functional redundancy in envelope acquisition such that envelopment proceeds if either is present but is abrogated if both are absent. Third, secondary envelopment of HSV -1 follows a similar pathway to other alphaherpesviruses but has distinct molecular requirements. To further characterize the involvement of gE/gi in secondary envelopment I examined specific contributions of the gE CT domain and identified regions of this domain that specifically contributed to this process. Additionally, I identified two tegument proteins, VP22 and ULll that bound to both gD and gE suggesting a plausible method by which gD and gE may interact with the nucleocapsid. Finally I characterized the role of specific regions of the gE CT domain in directing both cell-to-cell spread of infectious virions and trafficking of gE/gi. I demonstrated that simply localizing gE/gi to the site of virion envelopment is insufficient to mediate cell-to-cell spread. Furthermore, gE CT domain mutants that do not spread efficiently from cell-to-cell are not targeted to the apical surface. These findings imply that the gE CT domain has an additional role, beyond mediating secondary envelopment, in the trafficking of HSV.
School of Medicine
Farnsworth, Aaron Quinn, "The role of herpes simplex virus glycoprotein gE/gI in virus envelopment and egress" (2007). Scholar Archive. 800.