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Membrane protein lateral interactions control Semliki Forest virus budding
M Ekström1, P Liljeström, H Garoff
1Department of Molecular Biology, Karolinska Institute, Huddinge, Sweden.
Abstract:
Semliki Forest virus, SFV, directs the synthesis of two membrane proteins, p62 and E1, which form a p62E1 heterodimer in the endoplasmic reticulum. After being transported to the plasma membrane (PM), they are incorporated into the virus membrane during the process of virus budding. Electronmicroscopic analyses of the envelope in matured virus show that the heterodimers are clustered into trimeric structures (spikes) which further form a regular surface lattice with T = 4. In this work we have used a genetic approach to study the importance of the trimerization event for virus budding. We have coexpressed a budding competent form of the virus heterodimer with another one which cannot be used for particle formation because of a defect in nucleocapsid (NC) binding. We show that the NC binding-deficient heterodimer is able to inhibit the budding of the competent one in a concentration-dependent manner and that the NC binding-competent heterodimers can rescue the incompetent ones into virus particles. This suggests that the heterodimers are complexed together, probably into the trimeric structures (spikes), at the PM to expose a multivalent binding site for the NC and thereby drive efficient virus budding.
Insights
Semliki Forest virus (SFV) membrane proteins p62 and E1 form trimers essential for virus budding. Genetic analysis reveals these trimers bind nucleocapsid, driving efficient virus particle formation.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Semliki Forest virus (SFV) synthesizes p62 and E1 membrane proteins.
- These proteins form heterodimers in the endoplasmic reticulum and are transported to the plasma membrane.
- Mature SFV particles display trimeric spikes of p62E1 heterodimers forming a T=4 lattice.
Purpose of the Study:
- To investigate the role of p62E1 heterodimer trimerization in Semliki Forest virus budding.
- To understand the mechanism by which nucleocapsid (NC) binding influences virus particle formation.
Main Methods:
- Co-expression of budding-competent and NC binding-deficient SFV heterodimers.
- Genetic manipulation to create defects in nucleocapsid binding.
- Analysis of virus budding efficiency and particle formation.
Main Results:
- NC binding-deficient heterodimers inhibit budding of competent heterodimers in a concentration-dependent manner.
- Competent heterodimers can rescue incompetent ones, facilitating their incorporation into virus particles.
- Trimerization of p62E1 heterodimers at the plasma membrane is crucial for efficient virus budding.
Conclusions:
- Heterodimer complexation into trimers at the plasma membrane is essential for Semliki Forest virus budding.
- Trimeric structures likely provide a multivalent binding site for the nucleocapsid, driving efficient virus budding.