Structural and Functional Features of the Reovirus ?1 Tail.

ABSTRACT: Mammalian orthoreovirus attachment to target cells is mediated by the outer capsid protein ?1, which projects from the virion surface. The ?1 protein is a homotrimer consisting of a filamentous tail, which is partly inserted into the virion; a body domain constructed from ?-spiral repeats; and a globular head with receptor-binding properties. The ?1 tail is predicted to form an ?-helical coiled coil. Although ?1 undergoes a conformational change during cell entry, the nature of this change and its contributions to viral replication are unknown. Electron micrographs of ?1 molecules released from virions identified three regions of flexibility, including one at the midpoint of the molecule, that may be involved in its structural rearrangement. To enable a detailed understanding of essential ?1 tail organization and properties, we determined high-resolution structures of the reovirus type 1 Lang (T1L) and type 3 Dearing (T3D) ?1 tail domains. Both molecules feature extended ?-helical coiled coils, with T1L ?1 harboring central chloride ions. Each molecule displays a discontinuity (stutter) within the coiled coil and an unexpectedly seamless transition to the body domain. The transition region features conserved interdomain interactions and appears rigid rather than highly flexible. Functional analyses of reoviruses containing engineered ?1 mutations suggest that conserved residues predicted to stabilize the coiled-coil-to-body junction are essential for ?1 folding and encapsidation, whereas central chloride ion coordination and the stutter are dispensable for efficient replication. Together, these findings enable modeling of full-length reovirus ?1 and provide insight into the stabilization of a multidomain virus attachment protein.IMPORTANCE While it is established that different conformational states of attachment proteins of enveloped viruses mediate receptor binding and membrane fusion, less is understood about how such proteins mediate attachment and entry of nonenveloped viruses. The filamentous reovirus attachment protein ?1 binds cellular receptors; contains regions of predicted flexibility, including one at the fiber midpoint; and undergoes a conformational change during cell entry. Neither the nature of the structural change nor its contribution to viral infection is understood. We determined crystal structures of large ?1 fragments for two different reovirus serotypes. We observed an unexpectedly tight transition between two domains spanning the fiber midpoint, which allows for little flexibility. Studies of reoviruses with engineered changes near the ?1 midpoint suggest that the stabilization of this region is critical for function. Together with a previously determined structure, we now have a complete model of the full-length, elongated reovirus ?1 attachment protein.

SUBMITTER: Dietrich MH 

PROVIDER: S-EPMC6026731 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature