A trans -Golgi Network Resident Protein, golgin-97, Accumulates in Viral Factories and Incorporates into Virions during Poxvirus Infection

Abstract

Poxviruses are the only DNA viruses known to replicate and assemble in the cytoplasm of infected cells. Poxvirus morphogenesis is a complicated process in which four distinct infectious forms of the virus are produced: intracellular mature virus, intracellular enveloped virus, cell-associated enveloped virus, and extracellular enveloped virus. The source of primary membrane wrapping the intracellular mature virus, the first infectious form, is still unknown. Although the membrane was suggested to originate from the endoplasmic reticulum-Golgi intermediate compartment, none of the marker proteins from this or any other cell compartments has been found in the intracellular mature virus. Thus, it was hypothesized that the membrane is either extensively modified by the virus or synthesized de novo. In the work described here, we demonstrate that a host cell protein residing in the trans-Golgi network membrane, golgin-97, is transported to the sites of virus replication and assembly and becomes incorporated into the virions during poxvirus infection. Inside the virion, golgin-97 is associated with the insoluble core protein fraction. Being able to adopt a long rod-like structure, the protein apparently extends through the virion envelope and protrudes from its surface. Here we discuss the potential role and functions of golgin-97 in poxvirus replication and propose two working models.Poxviruses are large enveloped double-stranded DNA viruses with a complex morphology. Vaccinia virus (VV), the most extensively studied member of the Poxviridae, possesses a genome of approximately 192 kbp in size that encodes over 200 proteins whose expression is temporally regulated (22). Unlike other DNA viruses, VV replicates and assembles in the perinuclear compartments within the cytoplasm, termed viral factories or virosomes (22). The process of virus morphogenesis is very complicated and occurs in several stages. It begins with the assembly of membrane crescents around electron-dense material containing viral DNA and core proteins (11), leading to formation of spherical immature virus (IV). This step is followed by a series of proteolytic cleavages and condensation of the virus core, transforming IV into oval or brick-shaped intracellular mature virus (IMV), the first infectious form of VV (21). IMV represents the majority of produced virions and remains trapped inside the cell until its lysis. A subfraction of IMV moves on microtubules from the viral factories to the trans-Golgi network (TGN) (30) to acquire two additional membranes and become intracellular enveloped virus (IEV). Transported to the cell surface along microtubule networks (5, 9, 27, 38), IEV particles bud through the plasma membrane and lose the outermost envelope. This process generates cellassociated enveloped virus (CEV). CEV induces formation of actin tails that propel the particles, now referred to as extracellular enveloped virions (EEV), outside the cell and facilitates cell-to-cell and long-range dissemination of the virus.The origin of the virion membran...

Membrane Assembly during the Infection Cycle of the Giant Mimivirus

“…First and foremost is the origin of inner membrane layers that are present in all NCLDV virions. For Vaccinia membrane biogenesis, ER-Golgi intermediate compartment (ERGIC) membranes were suggested as a source of viral membranes [10], [11], [41], but other studies implied that Vaccinia inner membrane derives from host ER [12], [13], [22], [39]. ER network was also proposed as the source of the ASFV internal membrane [16]–[18], [42].…”

The golgin PpImh1 mediates reversible cisternal stacking in the Golgi of the budding yeast Pichia pastoris

“…Golgins such as GM130/golgin-95 (also known as GOLGA2) and p115 (also known as USO1) were found to be components of this matrix, and with their elongated structure, it was suggested that golgins function in the maintenance and establishment of Golgi structure (Slusarewicz et al, 1994;Nakamura et al, 1995;Waters et al, 1992). Knockdown of Golgin-97, Golgin-245 and GCC185 (also known as GOLGA1, GOLGA4 and GCC2, respectively) have been shown to affect the Golgi structure, suggesting a role for golgins in Golgi structure maintenance (Lu et al, 2004;Derby et al, 2007;Alzhanova and Hruby, 2006). Recently it has been reported that efficient stacking occurs in the absence of GRASP65 and/or GRASP55 when either of these two golgins is overexpressed (Lee et al, 2014).…”

Characterization of the VP39 envelope protein from Singapore grouper iridovirus

“…The intracellular distribution and dynamic changes of SGIV VP39 in infected cells revealed that VP39 ultimately localizes to the VAS. The major structural proteins are expected to localize to the VAS, as are immature virions and intracellular mature virions (Alzhanova et al 2006;VanSlyke et al 1994). Thus, it is reasonable to infer that the major viral structural protein VP39 is involved in SGIV replication and assembly.…”