Insights into the Fusion Mechanism of Herpes Simplex Virus Type 1 Glycoprotein B.
Silverman, Jessica.
2013
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Abstract: Herpesviruses are a diverse family of enveloped double-stranded DNA viruses that infect a wide range of animal hosts, including humans. These viruses enter cells by fusion of the viral envelope with a host cell membrane using conserved fusion glycoprotein B (gB) and its heterodimeric activator gH/gL plus additional nonconserved proteins. This complexity sets herpesviruses apart from most... read moreother enveloped viruses, which require only one or two proteins for entry, and resembles cellular fusion processes. However, the mechanism of herpesvirus entry is not well defined. Herpes Simplex virus (HSV) causes mucocutaneous lesions as well as severe conditions such as ocular infections and encephalitis. HSV has provided an excellent system for studying herpesvirus entry. Structural, biochemical and functional characterization of the four viral proteins required for HSV membrane fusion, gD, gB and gH/gL, has defined their functions, but the mechanism remains elusive. In this work, we set out to answer several questions about how gB and gH/gL are regulated. It is presumed that gB catalyzes fusion by undergoing conformational changes that provide the energy for this process, and that gH/gL plays a role in activating gB, likely via direct interaction of their ectodomains. Additional sources of regulation may come from the intraviral cytoplasmic domain of gB, which is thought to repress fusion, and the short cytoplasmic tail of gH, which may be involved in activating gB, possibly via a direct interaction with the gB cytoplasmic domain. However, the potential regulatory mechanisms of these intraviral domains remains unknown. Here, we show that the cytoplasmic domain of gB represses its fusion activity via a unique mechanism requiring sequences that exhibit membrane binding activity and preservation of the membrane-bound conformation. We provide the first structural model of this native conformation and propose that structural studies of the cytoplasmic domain must involve membrane. Additionally, we propose that the gH cytoplasmic tail regulates the fusion activity of gB via an indirect mechanism, perhaps involving membrane interaction. Finally, we show that the postfusion conformation of gB tolerates several mutations believed to destabilize this conformation, supporting previous conclusions that the postfusion form of gB is highly stable. Most importantly, these experiments tell us that membrane plays a critical role in gB function.
Thesis (Ph.D.)--Tufts University, 2013.
Submitted to the Dept. of Molecular Microbiology.
Advisor: Ekaterina Heldwein.
Committee: Joan Mecsas, Ralph Isberg, and Linc Sonenshein.
Keywords: Virology, Biochemistry, and Molecular biology.read less - ID:
- 2801pt46s
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