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The small envelope glycoprotein (GS) of equine arteritis virus folds into three distinct monomers and a
A A de Vries1, M J Raamsman, H A van Dijk
1Department of Infectious Diseases and Immunology, Veterinary Faculty, Utrecht University, The Netherlands.
Abstract:
The small membrane glycoprotein (GS) of equine arteritis virus (EAV) is a minor virion component but is abundantly expressed in EAV-infected cells. In this study, we have analyzed its membrane topology, folding, oligomerization, and intracellular transport. We show that GS is a class I integral membrane protein with one functional N-glycosylation site. Gel electrophoresis under nonreducing conditions revealed that GS occurs in EAV-infected cells in four monomeric conformations and as disulfide-linked homodimers. The slowest-migrating monomeric form corresponded to the fully reduced GS protein; the three faster-migrating monomeric species are probably generated by the formation of alternative intrachain disulfide bonds between the three luminal cysteines in the molecule. The GS monomers were selectively retained in the endoplasmic reticulum, as judged by their permanent susceptibility to endoglycosidase H, whereas the GS dimers were specifically incorporated into virus particles and became endoglycosidase H resistant and sialylated during passage through the Golgi apparatus.
Insights
The equine arteritis virus (EAV) small membrane glycoprotein (GS) forms monomers and dimers. Dimers are incorporated into virus particles, while monomers are retained in the endoplasmic reticulum.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- The small membrane glycoprotein (GS) is a minor component of equine arteritis virus (EAV) virions.
- GS is abundantly expressed in EAV-infected cells, suggesting a significant role.
Purpose of the Study:
- To investigate the membrane topology, folding, oligomerization, and intracellular transport of the EAV GS protein.
- To elucidate the functional significance of different GS conformations and their cellular localization.
Main Methods:
- Analysis of GS protein using gel electrophoresis under nonreducing conditions.
- Assessment of N-glycosylation and intracellular transport using endoglycosidase H susceptibility.
- Studying protein conformations, disulfide bond formation, and intracellular trafficking.
Main Results:
- GS is a class I integral membrane protein with one N-glycosylation site.
- GS exists as four monomeric conformations and disulfide-linked homodimers in infected cells.
- Monomeric GS is retained in the endoplasmic reticulum, while dimeric GS is incorporated into virus particles and processed through the Golgi apparatus.
Conclusions:
- The oligomerization state of GS dictates its intracellular transport and fate.
- Dimerization is crucial for GS incorporation into EAV virions and subsequent maturation.
- Differential retention of GS monomers and dimers highlights distinct cellular pathways.