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Assembly of the matrix protein of simian immunodeficiency virus into virus-like particles
S A González1, J L Affranchino, H R Gelderblom
1Department of Molecular Biology, University of Brussels (ULB), Belgium.
Abstract:
To obtain a better understanding of the processes of assembly and morphogenesis of simian immunodeficiency virus (SIV), recombinant vaccinia viruses containing regions of the gag-pol open reading frame were constructed and their intracellular expression as well as the ability of the Gag polypeptides to be released into the culture medium as constituents of virus-like particles were studied. Biochemical and electron microscopy analyses of cells infected with a recombinant expressing only the SIV matrix (MA) domain of the Gag polyprotein (v-p17 gag) showed that this protein self-assembles into 100-nm virus-like particles which are released into the culture medium. Interestingly, coexpression of SIV MA and Env proteins resulted in incorporation of gp120 and gp41 proteins into the recombinant p17-made particles. In addition when a positively charged domain of SIV MA (residues 26-33), which is highly conserved among all HIV and SIV MA proteins, was mutated into an acidic region, particle release was abolished without affecting protein expression, processing, or stability. Further characterization of the phenotype of this mutant by electron microscopy indicated that this mutant was blocked at the stage of assembly. These results suggest that SIV MA protein, along with its function in myristic acid-mediated membrane targeting, has intrinsic information for self-assembly as well as incorporation of viral Env glycoproteins into particles.
Insights
The simian immunodeficiency virus matrix protein self-assembles into virus-like particles and incorporates Env glycoproteins. A specific mutation prevents particle release, highlighting the matrix protein's role in SIV assembly.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Understanding simian immunodeficiency virus (SIV) assembly and morphogenesis is crucial for developing antiviral strategies.
- The Gag polyprotein plays a central role in retroviral particle formation and release.
Purpose of the Study:
- To investigate the self-assembly properties of the SIV matrix (MA) protein.
- To determine the role of the SIV MA protein in virus-like particle (VLP) formation and Env glycoprotein incorporation.
Main Methods:
- Construction and infection with recombinant vaccinia viruses expressing SIV gag-pol regions.
- Biochemical analysis of protein expression, processing, and release.
- Electron microscopy to visualize virus-like particles and cellular assembly stages.
Main Results:
- The SIV MA protein self-assembles into 100-nm VLPs released into the culture medium.
- Co-expression of MA and Env proteins leads to gp120 and gp41 incorporation into VLPs.
- Mutation of a conserved positively charged domain in MA (residues 26-33) abolishes VLP release and blocks assembly.
Conclusions:
- The SIV MA protein possesses intrinsic information for self-assembly into VLPs.
- The MA protein mediates the incorporation of viral Env glycoproteins into assembling particles.
- A specific charged region within the MA protein is essential for SIV particle assembly and release.