Year of Publication

2017

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Medicine

Department

Molecular and Cellular Biochemistry

First Advisor

Dr. Rebecca Dutch

Abstract

Enveloped viruses, such as HIV, influenza, and Ebola, utilize surface glycoproteins to bind and fuse with a target cell membrane. This fusion event is necessary for release of viral genomic material so the virus can ultimately reproduce and spread. The recently emerged Hendra virus (HeV) is a negative-sense, single-stranded RNA paramyxovirus that presents a considerable threat to human health as there are currently no human vaccines or antivirals available. The HeV utilizes two surface glycoproteins, the fusion protein (F) and the attachment protein (G), to drive membrane fusion. Through this process, the F protein undergoes an irreversible conformational change, transitioning from a meta-stable pre-fusion conformation to a more thermodynamically stable post-fusion structure. Understanding the elements which control stability of the pre-fusion state and triggering to the post-fusion conformation is important for understanding F protein function. Studies that replace or mutate the TM domain of the F protein of several viruses implicated the TM domain in the fusion process, but the structural and molecular details in fusion remain unclear. Previously, analytical ultracentrifugation was used to demonstrate that isolated TM domains of HeV F protein associate in a monomer-trimer equilibrium. To determine factors driving this association, we analyzed the sequence of several paramyxovirus F protein TM domains and found a heptad repeat of β-branched residues. Analysis of the HeV F TM domain specifically revealed a heptad repeat leucine-isoleucine zipper motif (LIZ). Replacement of the LIZ with alanine resulted in dramatically reduced TM-TM association. Mutation of the LIZ in the whole protein resulted in decreased protein expression and pre-fusion conformation. To further understand the role of the TM domain, the TM domain was targeted as a potential modulator of F protein stability and function. Exogenous HeV F TM constructs were co-expressed with the full length F protein in Vero cells to analyze the effects on protein expression. Co-expression of the exogenous HeV F TM constructs dramatically reduced the expression of HeV F. However, the co-expression of exogenous HeV F TM constructs with a different paramyxovirus F protein, PIV5 F, did not strongly affect PIV5 F expression levels, suggesting that the interaction of the exogenous TM constructs is specific. Fusion assays revealed that HeV F TM constructs dramatically reduced HeV F, but not PIV5 F fusion activity. We hypothesize that the short exogenous HeV TM constructs associate with the TM domain from full-length HeV F, resulting in pre-mature triggering or protein misfolding. The work presented here demonstrates that specific elements in the TM domain contribute to TM association and pre-fusion protein stability. Furthermore, targeting these interactions may be a viable approach for antiviral development against this important pathogen.

Digital Object Identifier (DOI)

https://doi.org/10.13023/ETD.2017.172

Included in

Biochemistry Commons

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