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Figure 7 | Virology Journal

Figure 7

From: Uncoupling GP1 and GP2 expression in the Lassa virus glycoprotein complex: implications for GP1 ectodomain shedding

Figure 7

Hypothetical arenaviral glycoprotein expression pathway and secretory forms. Arenaviral glycoprotein (GP) mRNA is transcribed from plasmid DNA constructs in the host cell (1), and directed to the rough endoplasmic reticulum (RER) for translation. The nascent polyprotein is directed to the RER lumen by the SP, where SPases cleave SP from the GP polyprotein precursor (2). In the RER the GP precursor is cleaved by SKI-1/S1P to yield GP1 and GP2 (3). Wild-type GP may be comprised of covalently-linked GP1 and GP2, and associated SP (3a). In GPCΔTM (3b) and GPCΔTMΔIC (3c) truncated GP2 subunits may associate covalently with GP1. The role of SP in these variants is unknown. A GP fraction expressed from constructs GPCΔTM and GPCΔTMΔIC that is not processed by SKI-1/S1P could shuttle uncleaved polyprotein to the glycosylation pathway (3d). The SP’s role here is also unknown. Glycosylation of GP1 and GP2 is mediated by RER or Golgi glycosyltransferases (4). Membrane-bound vesicles transport proteins to the Golgi cis face where processing and assembly occur. Assembled and glycosylated GP complex or subunits are packaged in exocytic vesicles that emerge from the Golgi trans face and are directed toward the plasma membrane (5). The GP complex is anchored via the GP2 transmembrane domain (6a, b). Complexed heterodimeric GP1–GP2 is displayed in 6a, whereas GP spike trimer in a hypothetical prefusion form is shown in 6b. Extracellular GP1 from expression of wild-type GPC may be produced by protease-mediated ectodomain shedding, or an isoform of secreted GP1. The potential forms of the GP complex and subunits are outlined in 7. Monomeric sGP1 and homodimer (7a), soluble monomeric GP2 and GP1, complexed heterodimer, or the potentially uncleaved GP precursor (in etched box) derived from GPCΔTM (7b) and GPCΔTMΔIC (7c) are shown. Legend box: Graphic representations of relevant components.

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