Membrane Remodeling by the Double-Barrel Scaffolding Protein of Poxvirus

Abstract

In contrast to most enveloped viruses, poxviruses produce infectious particles that do not acquire their internal lipid membrane by budding through cellular compartments. Instead, poxvirus immature particles are generated from atypical crescent-shaped precursors whose architecture and composition remain contentious. Here we describe the 2.6 Å crystal structure of vaccinia virus D13, a key structural component of the outer scaffold of viral crescents. D13 folds into two jellyrolls decorated by a head domain of novel fold. It assembles into trimers that are homologous to the double-barrel capsid proteins of adenovirus and lipid-containing icosahedral viruses. We show that, when tethered onto artificial membranes, D13 forms a honeycomb lattice and assembly products structurally similar to the viral crescents and immature particles. The architecture of the D13 honeycomb lattice and the lipid-remodeling abilities of D13 support a model of assembly that exhibits similarities with the giant mimivirus. Overall, these findings establish that the first committed step of poxvirus morphogenesis utilizes an ancestral lipid-remodeling strategy common to icosahedral DNA viruses infecting all kingdoms of life. Furthermore, D13 is the target of rifampicin and its structure will aid the development of poxvirus assembly inhibitors.

Structure of Sputnik, a virophage, at 3.5-Å resolution

“…A similar double jelly-roll was found in the plant RNA cowpea mosaic virus (18) and later in PBCV-1 (19). Other viruses with double jelly-roll MCP structures include the dsDNA PRD1 bacterial phage (20), the marine phage PM2 (21,22), the archaeal Sulfolobus turreted icosahedral virus (23,24), and vaccinia virus (25,26). Furthermore, there are numerous other viruses that most likely also have double jelly-roll MCPs according to sequence comparisons, as for instance Mimivirus (1) and African swine fever virus.…”

Structure of faustovirus, a large dsDNA virus

“…The MCP forms a homotrimer with each monomer consisting of two sequential jelly-roll folds. Similar pseudohexameric capsomer structures can be found in many other viral capsid proteins including adenovirus (7), the phage PRD1 (8), PBCV-1 (9), the virophage Sputnik (10), and the scaffolding protein of vaccinia virus (11,12). A single jelly-roll fold consists of eight antiparallel β-strands that are named from B to I along the polypeptide sequence.…”

“…A search for comparable domains using secondary structural matching (13) found no structural homologs with known function. The faustovirus MCP crown domain is yet another example of how a common structural fold can be used to accommodate a wide range of structural decorations (7)(8)(9)(10)(11)(12). It is currently unclear whether the crown domain that forms the surface of the virus plays a role in host recognition or cell entry.…”

Toward High-Resolution Cryo-Electron Microscopy: Technical Review on Microcrystal-Electron Diffraction

“…Owing to this reason, electron diffraction has been restricted to be used with 2D crystals that comprise 1~2 thin layers of a well-ordered 2D crystalline lattice. Over the past decades, 2D electron crystallography has been used successfully to obtain near-atomic-resolution structures of membrane proteins surrounded by lipid layers (Gonen et al, 2005;Hyun et al, 2011). However, most structures analyzed by this technique have only moderate resolution (4~10 A) as electrons have extremely high energies and cause large amounts of radiation damage to the crystals, thus resulting in the loss of structural information (Glaeser, 1971).…”