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The nucleocapsid-binding spike subunit E2 of Semliki Forest virus requires complex formation with the E1 subunit for
Abstract:
Alphaviruses, such as Semliki Forest virus (SFV), mature by budding at the plasma membrane (PM) of infected cells and enter uninfected ones by a membrane fusion process in the endosomes. Both processes are directed by the p62/E2-E1 membrane protein heterodimer of the virus. The p62 protein, or its mature form E2, provides a cytoplasmic protein domain for interaction with the nucleocapsid (NC) of the virus, and the E1 protein functions as a membrane fusogen. We have previously shown that the p62/E2 protein of SFV controls the membrane fusion activity of E1 through its complex formation with the latter (A. Salminen, J. M. Wahlberg, M. Lobigs, P. Liljeström, and H. Garoff, J. Cell Biol. 116:349-357, 1992). In the present work, we show that the E1 protein controls the NC-binding activity of p62/E2. We have studied E1 expression-deficient SFV variants and shown that although the p62/E2 proteins can be transported to the PM they cannot establish stable NC associations.
Insights
Semliki Forest virus (SFV) E1 protein regulates p62/E2 binding to the nucleocapsid. E1 deficiency prevents p62/E2 association with the nucleocapsid, impacting viral maturation.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Alphaviruses like Semliki Forest virus (SFV) bud from the plasma membrane and infect cells via endosomal fusion.
- Viral maturation and entry depend on the p62/E2-E1 membrane protein heterodimer.
- p62/E2 interacts with the nucleocapsid, while E1 mediates membrane fusion.
Purpose of the Study:
- To investigate the role of the E1 protein in regulating the nucleocapsid-binding activity of p62/E2.
- To understand the interplay between E1 and p62/E2 in viral assembly and infection.
Main Methods:
- Analysis of E1 expression-deficient SFV variants.
- Assessment of p62/E2 protein transport to the plasma membrane.
- Evaluation of nucleocapsid (NC) association with p62/E2.
Main Results:
- E1 expression-deficient SFV variants show p62/E2 proteins transported to the plasma membrane.
- Despite correct localization, p62/E2 proteins in these variants fail to form stable associations with the nucleocapsid.
- This indicates E1 is crucial for establishing stable NC-p62/E2 interactions.
Conclusions:
- The E1 protein is essential for controlling the nucleocapsid-binding activity of the p62/E2 protein.
- E1's function extends beyond membrane fusion to include regulation of viral component interactions necessary for maturation.