Ebola is an NIAID category A priority pathogen that causes massive hemorrhage in its victims. Because of its high mortality rate (up to 90%), Ebola is a serious threat to global health. There are no anti-viral agents to combat Ebola. The long-term goal of this work is to identify a low molecular weight inhibitor of Ebola virus fusion. The precedent is the identification of peptides and small molecules that inhibit the fusion activities of influenza, paramyxoviruses, and HIV; the inhibitors prevent conversion of the viral fusion proteins from their native, to their fusion-active, states. There are currently no assays for Ebola fusion or for fusion-relevant conformational changes in its fusion protein, GP. Before anti-Ebola fusion inhibitors can be identified, assays and reagents must be developed, and basic information about the fusion mechanism must be obtained. The major goal of this proposal is to fulfill these prerequisites for the long-term goal. [unreadable] [unreadable] The specific aims are: (1) to develop a fusion assay for the Ebola virus GP; (2) to characterize basic properties of Ebola virus fusion; and (3) to develop assays for fusion-relevant conformational changes in GP. [unreadable] [unreadable] The work is modeled on studies conducted by the Principal Investigator on influenza virus, Semliki Forest virus, vesicular stomatitis virus, and retroviruses. It will employ a combination of molecular virological, biophysical, and biochemical techniques. The applicant's work will be performed in a BL2 laboratory using pseudotype particles bearing GP or cells expressing GP. Key findings will be tested with Ebola virus in a BL4 laboratory by collaborators at USAMRIID. For example, under Aim 2, mutant GPs will be identified that are severely defective in fusion. The collaborators will engineer the mutants into Ebola virus, using a reverse genetics system, and test their infectivity and pathogenicity. If the mutants are highly compromised in infectivity and pathogenicity, it would indicate that fusion is a good target for anti-Ebola intervention. The stage would then be set to screen for inhibitors of Ebola virus fusion and to test their efficacy in animal models. [unreadable] [unreadable]