Final Activity Report Summary - PESTIVIRUS FUSION (Mechanism of BVDV fusion) Bovine viral diarrhoea virus (BVDV) belongs to the genus Pestivirus, which also comprises important animal pathogens like classical swine fever virus (CSFV) and border disease virus (BDV). Both classical swine fever and bovine viral diarrhoea are reportable diseases in the European Union and cause major economic losses in agricultural animal production. While the annual cost of BVDV infections only to the UK cattle industry has been estimated at approximately 73 million euros, the overall costs and losses of the CSFV epidemic in 1997-1998 in the EU have been estimated at approximately 2 billion euros. Pestiviruses are small (40-60nm) enveloped RNA viruses, which consist of the Core protein and the three glycoproteins Erns, E1 and E2, anchored in the viral lipid envelope. These glycoproteins carry essential functions during the viral life cycle like the initial attachment of the virus particle to specific molecules on the surface the host cell. They also induce fusion of the viral lipid envelope with the cellular membrane leading to release of the viral genome into the host cell cytoplasm. The glycoprotein Erns has been shown to be involved during viral invasion into the host cell, but it also contains a ribonucleolytic activity - a feature that renders Erns unique among all viral glycoproteins known to date. The main goal of this project was to understand the roles of the pestiviral glycoproteins in the viral life cycle and the respective underlying mechanisms. We used X-ray crystallography, a technique commonly used to elucidate the atomic structures of proteins and other biological macromolecules, to solve the crystal structure of BVDV Erns. Surprisingly, the closest structural homologue of Erns known so far is a secreted plant protein, suggesting a common ancestor between pestiviral Erns and this plant protein, which has been acquired by pestiviruses at one point during evolution. Furthermore, cocrystallisation experiments with potential substrates illustrate the structural basis of the substrate specificity of this enzyme. They also enable us to provide important insights into the enzymatic mechanism leading to the hydrolysis of the RNA substrate.
