Molecular mechanisms of flavivirus membrane fusion

Membrane fusion plays an essential role in the entry of enveloped viruses into cells and in intracellular transport processes. In this project we will investigate the molecular and structural determinants of membrane fusion in a viral system, using tick-borne encephalitis (TBE) virus as a model. TBE virus is a flavivirus, which is closely related to a number of other important arthropod-transmitted human pathogens such as yellow fever, Japanese encephalitis, dengue, and West Nile virus and also shares many of its molecular biological features with hepatitis C virus. Viral fusion is mediated by specific envelope proteins (fusion proteins), and so far two completely different structural classes, class I and class II have been identified. The atomic structure of the TBE virus fusion protein (E) has been determined by X-ray crystallography. It represents a prototype class II viral fusion protein and differs structurally and mechanistically from the class I proteins that are found in ortho- and paramyxoviruses, retrovirsuses, and filoviruses. Since the atomic structure of the fusion protein is known, the TBE virus system is an ideal model for investigating the details of the class II fusion protein-mediated membrane fusion machinery. In previous work we have shown that fusion of TBE virus requires acidic pH as a trigger for initiating a change from the metastable conformation of the fusion protein to an intermediate state that induces membrane fusion and leads to a stable post-fusion structure. In the context of this project we will a.) attempt to identify the structural elements involved in this conformational change by the generation of monoclonal antibodies specific for the low pH conformation, b.) investigate the characteristics of the TBE virus fusion process using in vitro liposome fusion models, and c.) carry out structural studies on the low-pH conformation using electron microscopy and X-ray crystallography. The latter studies will be conducted in collaboration with specialists at the CNRS in Paris, France. The key objective of this poject is to understand the mechanism and structural requirements of flavivirus fusion, which, as shown in other viral systems, such as HIV, can lead to the identification of specific targets for the development of antiviral agents.

Membrane fusion plays an essential role in the entry of enveloped viruses into cells and in intracellular transport processes. In this project we will investigate the molecular and structural determinants of membrane fusion in a viral system, using tick-borne encephalitis (TBE) virus as a model. TBE virus is a flavivirus, which is closely related to a number of other important arthropod-transmitted human pathogens such as yellow fever, Japanese encephalitis, dengue, and West Nile virus and also shares many of its molecular biological features with hepatitis C virus. Viral fusion is mediated by specific envelope proteins (fusion proteins), and so far two completely different structural classes, class I and class II have been identified. The atomic structure of the TBE virus fusion protein (E) has been determined by X-ray crystallography. It represents a prototype class II viral fusion protein and differs structurally and mechanistically from the class I proteins that are found in ortho- and paramyxoviruses, retrovirsuses, and filoviruses. Since the atomic structure of the fusion protein is known, the TBE virus system is an ideal model for investigating the details of the class II fusion protein-mediated membrane fusion machinery. In previous work we have shown that fusion of TBE virus requires acidic pH as a trigger for initiating a change from the metastable conformation of the fusion protein to an intermediate state that induces membrane fusion and leads to a stable post-fusion structure. In the context of this project we will a.) attempt to identify the structural elements involved in this conformational change by the generation of monoclonal antibodies specific for the low pH conformation, b.) investigate the characteristics of the TBE virus fusion process using in vitro liposome fusion models, and c.) carry out structural studies on the low-pH conformation using electron microscopy and X-ray crystallography. The latter studies will be conducted in collaboration with specialists at the CNRS in Paris, France. The key objective of this poject is to understand the mechanism and structural requirements of flavivirus fusion, which, as shown in other viral systems, such as HIV, can lead to the identification of specific targets for the development of antiviral agents.