Structural studies of pestivirus envelope glycoproteins

Pestiviruses belong to the family Flaviviridae with the most well-known being Bovine Viral Diarrhoea Virus, Border Disease Virus, and Classical Swine Fever Virus affecting cows, sheep, and pigs respectively. These viruses cause a large economic impact especially in the dairy and pig industries. As a result of being enveloped viruses, to enter the cytoplasm and replicate, they must first fuse their membrane with that of the cell’s endosome, in a process which requires a fusion protein. Pestiviruses require two envelope glycoproteins for this step: E2, likely involved with receptor interaction, and E1, likely the fusion protein. Reported within is the design of over 80 expression constructs, expression testing of 70, large scale production of 16 and the crystallisation of 7. As a result, two x-ray crystallography structures of the ectodomain of a putative pestivirus receptor bovine CD46 were solved. These structures revealed an interesting dimer, like that found in human CD46, although not reported previously. This dimer presents an interesting insight to the potential orientation of CD46 in the cell surface and could potentially play a role in anchoring the virus particles at sites of endocytosis. This thesis also presents the structure of two novel pestivirus E2 ectodomains from APPV and NRPV. These structures highlight the variety of pestivirus E2 structures and support the finding that E2 is not the fusion protein. Investigations into N-terminal disorder at low pH, such as in the late endosome, revealed that this was not the case for all pestiviruses. The more typical E2 proteins from BVDV, BDV, and CSFV all display evidence of structural changes at low pH while the more atypical pestiviruses APPV and NRPV do not. In addition, an interesting beta-hairpin was revealed towards the N-terminal region of all five E2 proteins which may play a role in receptor interaction.