African swine fever virus assembles a single membrane derived from rupture of the endoplasmic reticulum

Abstract

Collective evidence argues that two members of the nucleocytoplasmic large DNA viruses (NCLDVs) acquire their membrane from open membrane intermediates, postulated to be derived from membrane rupture. We now study membrane acquisition of the NCLDV African swine fever virus. By electron tomography (ET), the virion assembles a single bilayer, derived from open membrane precursors that collect as ribbons in the cytoplasm. Biochemically, lumenal endoplasmic reticulum (ER) proteins are released into the cytosol, arguing that the open intermediates are ruptured ER membranes. ET shows that viral capsid assembles on the convex side of the open viral membrane to shape it into an icosahedron. The viral capsid is composed of tiny spikes with a diameter of ∼5 nm, connected to the membrane by a 6 nm wide structure displaying thin striations, as observed by several complementary electron microscopy imaging methods. Immature particles display an opening that closes after uptake of the viral genome and core proteins, followed by the formation of the mature virion. Together with our previous data, this study shows a common principle of NCLDVs to build a single internal envelope from open membrane intermediates. Our data now provide biochemical evidence that these open intermediates result from rupture of a cellular membrane, the ER.

Localization of adenovirus morphogenesis players, together with visualization of assembly intermediates and failed products, favor a model where assembly and packaging occur concurrently at the periphery of the replication center

“…The open membrane, which holds the viral DNA, is progressively coated by capsid proteins to form an icosahedral particle, similarly to our observation of AdV capsid fragments engulfing the condensing core. A similar mechanism has been proposed for African swine fever virus (ASFV) [74]. Bacteriophage PM2, ASFV, and Mimivirus, all contain a membrane inside the icosahedral shell.…”

Virus-host interactions: insights from the replication cycle of the largeParamecium bursaria chlorella virus

“…Subsequently, cisternae are ruptured into a dense network of open, single bilayer membrane sheets that accumulate in the centre of the PBCV‐1 factories. These open sheets interact with a capsid protein to form pre‐capsids, as was shown to be the case for Vaccinia (Chlanda et al ., ), Mimivirus (Krijnse‐Locker et al ., ; Mutsafi et al ., ) and ASFV (Suárez et al ., ). Therefore, a general mechanism for the biogenesis of single internal membrane bilayers in viruses, as well as a role for these sheets as templates for crescents formation and capsid assembly, may exist.…”

Ultrastructural morphogenesis of a virus associated with lymphocystis-like lesions in parore Girella tricuspidata (Kyphosidae: Perciformes)

“…The ERGIC and TGN are involved in membrane biogenesis and virogenesis in poxviruses (Schmelz et al 1994, Risco et al 2002, Moss 2015. Detailed studies on the monotypic asfarid NCLDV ASFV have shown that ER is involved in the formation of the lipid internal membrane between the core shell and capsid (Cobbold et al 1996, Andrés et al 1998, 2002, Rouiller et al 1998, Epifano et al 2006, Windsor et al 2012, Salas & Andrés 2013, Suarez et al 2015, possibly due to col- Table 1 Figs. 17-18.…”

“…18. Crystalline array of mature nucleocapsids; ×5335 lapsed (Andrés et al 1998) or ruptured (Suarez et al 2015) ER cisternae pushing the 2 membranes together to form a unit-like membrane (Andrés et al 1998). Most NCLDV viruses have a membrane that separates the nucleocapsid from the external capsid (Xiao & Rossmann 2011), including LCDV (Heppell & Berthiaume 1992), and host membranes probably serve as a scaffold to which capsid and shell proteins bind (Chinchar et al 2011).…”

“…7d,e in Windsor et al 2012). However, zipper-like structures are aberrant structures (Rodríguez et al 2004, Epifano et al 2006, Salas & Andrés 2013, formed by rupture (Suarez et al 2015) not collapse (Andrés et al 1998) of ER, and they are not homologous with tER. Also, while tER occurred between profiles of swollen ER, they were not seen to derive from the ER.…”