Matthijn de Boer
Thursday 14 March 2013
Rift Valley fever virus Glycoproteins, Key to Entry and Control
Promotor: Prof. dr. R.J.M. Moormann
Defence: 14 March 2013
In this thesis we have focussed on the RVFV Gn and Gc glycoproteins, the keys for virus entry and virus control. RVFV is an emerging virus that has already spread across the African continent and to the Arabian Peninsula. RVFV outbreaks are characterized by abortion storms and high mortality among young animals. Adult animals are also affected but mortality in these animals is considerably lower. Humans can be infected by exposure to blood or other body fluids of viremic animals or via mosquito bite. RVFV has the potency to spread across large distances by as yet unknown mechanisms, explaining the need for established contingency plans in currently unaffected areas.
We aimed to develop control measures to protect livestock against RVFV infection. Antibodies directed against the Gn and Gc glycoproteins are able to neutralize the virus, which is the only established correlate of protection against RVFV infection. We have developed and characterized different veterinary vaccines that are considered safe for animals of all ages and evaluated their efficacy in mice and sheep animal models. Registration trials with one of our vaccines are currently being performed.
We have also investigated the RVFV entry mechanism and paid specific attention to the fusion process. We demonstrate that the abundantly cell surface expressed glycosaminoglycan heparan sulfate is required for efficient RVFV infection of different mammalian cells. Our studies confirm the hypothesis that after uptake of the virus by endocytosis RVFV membrane fusion is triggered by low pH. The activating pH and the kinetics of virus entry suggested that RVFV penetrates from late endosomal compartments. We demonstrate biochemically that exposure of virus particles to low pH results in the formation of highly stable multimers of the RVFV Gc glycoprotein. Mutagenesis of Gc in combination with biochemical and functional analyses suggested that proton binding by histidines in Gc plays a crucial role in the conformational rearrangements of the Gc fusion protein and in virus entry.