Structural polyprotein
Domain
Structural polyprotein: Contains two internal signal peptides that are necessary for directing translocation of the glycoproteins into the lumen of the endoplasmic reticulum.
Capsid protein
The capsid protein is probably attached to the viral membrane through the E2 signal peptide. This domain is also required for the localization of the capsid protein to the juxtanuclear region and subsequent virus assembly at the Golgi complex.
Function
Capsid protein
Capsid protein interacts with genomic RNA and assembles into icosahedric core particles 65-70 nm in diameter. The resulting nucleocapsid eventually associates with the cytoplasmic domain of E2 at the cell membrane, leading to budding and formation of mature virions from host Golgi membranes. Phosphorylation negatively regulates RNA-binding activity, possibly delaying virion assembly during the viral replication phase. Capsid protein dimerizes and becomes disulfide-linked in the virion. Modulates genomic RNA replication. Modulates subgenomic RNA synthesis by interacting with human C1QBP/SF2P32. Induces both perinuclear clustering of mitochondria and the formation of electron-dense intermitochondrial plaques, both hallmarks of rubella virus infected cells. Induces apoptosis when expressed in transfected cells.
Spike glycoprotein E2
Responsible for viral attachment to target host cell, by binding to the cell receptor. Its transport to the plasma membrane depends on interaction with E1 protein. The surface glycoproteins display an irregular helical organization and a pseudo-tetrameric inner nucleocapsid arrangement.
Spike glycoprotein E1
Class II viral fusion protein (By similarity). Fusion activity is inactive as long as E1 is bound to E2 in mature virion. After virus attachment to target cell and clathrin-mediated endocytosis, acidification of the endosome would induce dissociation of E1/E2 heterodimer and concomitant trimerization of the E1 subunits (By similarity). This E1 homotrimer is fusion active, and promotes release of viral nucleocapsid in cytoplasm after endosome and viral membrane fusion. The cytoplasmic tail of spike glycoprotein E1 modulates virus release. The surface glycoproteins display an irregular helical organization and a pseudo-tetrameric inner nucleocapsid arrangement (By similarity).
Post-translational modifications
Structural polyprotein: Specific enzymatic cleavages in vivo yield mature proteins. Two signal peptidase-mediated cleavages within the polyprotein produce the structural proteins capsid, E2, and E1. The E2 signal peptide remains attached to the C-terminus of the capsid protein after cleavage by the signal peptidase. Another signal peptide at E2 C-terminus directs E1 to the ER, with a similar mechanism.
Spike glycoprotein E1
Contains three N-linked oligosaccharides.
Capsid is phosphorylated on Ser-46 by host. This phosphorylation negatively regulates capsid protein RNA-binding activity (By similarity). Dephosphorylated by human PP1A (By similarity).
Cellular localization
- Capsid protein
- Virion
- Host cytoplasm
- Host mitochondrion
- The capsid protein is concentrated around Golgi region (By similarity). In the virion, it is probably associated to the viral membrane (By similarity).
- Spike glycoprotein E2
- Virion membrane
- Single-pass type I membrane protein
- Host Golgi apparatus membrane
- Single-pass type I membrane protein
- E1 and E2 form heterodimer in the endoplasmic reticulum before they are transported to and retained in the Golgi complex, where virus assembly occurs. E1 possesses an endoplasmic reticulum retention signal, and unassembled E2 and E1 subunits are retained in the endoplasmic reticulum. Presumably, assembly of E2 and E1 would mask the signal, thereby allowing transport of the heterodimer to the Golgi complex.
- Spike glycoprotein E1
- Virion membrane
- Single-pass type I membrane protein
- Host Golgi apparatus membrane
- Single-pass type I membrane protein
- E1 and E2 form heterodimer in the endoplasmic reticulum before they are transported to and retained in the Golgi complex, where virus assembly occurs. E1 possesses an endoplasmic reticulum retention signal, and unassembled E2 and E1 subunits are retained in the endoplasmic reticulum. Presumably, assembly of E2 and E1 would mask the signal, thereby allowing transport of the heterodimer to the Golgi complex.
Alternative names
Structural polyprotein, p110