The matrix protein VP40 is an indispensable component of viral assembly and budding by the Ebola virus, VP40 is a monomer in Solution, but can fold into hexameric and octameric states. two oligomeric conformations that play central roles in the Ebola viral life cycle. While the X-ray structures of monomeric and octameric VP40 have been determined, the structure of hexameric VP40 has only been solved by three-dimensional electron microscopy (EM) to a resolution of' similar to 30 angstrom. In this paper. we present the refinement of the EM reconstruction of truncated hexameric VP40 to similar to 20 angstrom and the Construction of an all-atom model (residues 44 212) using the EM model at similar to 20 angstrom and the X-ray structure of monomeric VP40 as templates. The hexamer model suggests that the monomer hexamer transition involves a conformational change in the N-terminal domain that is not evident during octamerization and therefore. may provide the basis for elucidating the biological function of VP40. Published by Elsevier Inc.