Structural Studies of Viral Hemorrhagic Fever Pathogenesis

In my laboratory, we are crystallizing proteins that play key roles in the pathogenesis and lethality of hemorrhagic fever viruses. The resulting crystal structures of these proteins will provide information seminal to the design of vaccines and inhibitors against the viruses as they exist naturally, and will also provide structural templates that would permit us to anticipate and rapidly respond to newly emerging and man-made versions of the virus and viral proteins.

Ebola Virus

There have been at least 10 recognized outbreaks of the Ebola virus, each with a 50-90% human case fatality. To date there are no available vaccines or treatments. An unusual feature of the viral genome is its ability to encode two different glycoproteins, sGP and GP, from the same gene. sGP and GP share 295 amino acids of N-terminal sequence, but a transcriptional editing event causes them to have different C-terminal sequences. The different C termini result in unique patterns of disulfide bonding, structures, and roles in pathogenesis. sGP forms an antiparallel dimer and is secreted in large quantities from infected cells. GP forms a parallel trimer on the viral surface, and functions in viral attachment, fusion, and tropism. GP may also cause some of the hemorrhagic symptoms seen in Ebola virus infection. Comparative structural analysis of sGP and GP should explain how two structures arise from the same sequence, and provide templates to guide the design of vaccines that elicit antibodies which target the virus rather than the secreted proteins. Additional crystal structures of these proteins in complex with human antibodies derived from survivors of Ebola virus infection will assist vaccine design.

An additional crystallographic target is the VP35 protein, a required component of the Ebola viral capsid and transcription complex. VP35 also blocks type I interferon activation of immunomodulatory genes and may play a significant role in Ebola virus suppression of the host immune system. Hence, structural analysis of the VP35 protein may provide insights into viral replication and type I interferon suppression and will provide the structural basis for the design of anti-viral compounds and attenuated viral strains.

Dengue Virus

Dengue virus is a mosquito-borne flavivirus that causes up to 100 million infections per year. Infection with dengue virus results in either Dengue Fever or the much more severe disease Dengue Hemorrhagic Fever (DHF). Development of DHF usually occurs upon secondary infection with a different viral subtype, or in infants born to dengue-immune mothers, suggesting that in some circumstances antibodies against the virus may actually enhance disease severity. Potential antibody-mediated enhancement of dengue virus infection is a major concern in the testing and use of vaccines against dengue. Crystal structures of human antibodies in complex with dengue antigens will provide a structural basis for understanding this phenomenon and will offer novel templates for design of safe vaccines.