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The "V3" domain is a determinant of simian immunodeficiency virus cell tropism
F Kirchhoff1, K Mori, R C Desrosiers
1New England Regional Primate Research Center, Harvard Medical School, Southborough, Massachusetts 01772-9102.
Abstract:
Thirty-one different mutant forms of simian immunodeficiency virus (SIVmac) were created with changes in the region of env corresponding to the V3 domain of HIV-1. Sixteen of these mutants had one amino acid change, 12 had two changes, two had three changes, and one had four changes in the SIVmac "V3" loop. The ability of the mutant viruses to replicate in CEMx174 cells, rhesus monkey peripheral blood mononuclear cells, and rhesus monkey alveolar macrophages was investigated. Ten of the mutant viruses replicated with approximately wild-type kinetics in all three cell types. Of the 31 mutants, 22 were able to replicate in one or more of the cell types. Thus, this region of SIVmac gp120 is quite tolerant to change. Nine of the mutants replicated poorly or not at all in any of the cells tested. The lack of replication competence of some of the mutants was associated with inefficient proteolytic processing of the gp160 precursor. Some mutations had dramatic differential effects in different cell types. For example, changing P to S at position 321 and M to I at position 325 drastically reduced replication in macrophages and CEMx174 cells but had no effect on replication in peripheral blood mononuclear cells. Mutants with altered tropism were blocked at an early stage that includes virus entry into cells. Thus, sequences in SIVmac that correspond to V3 in HIV-1 can affect virus entry and cell tropism in a manner analogous to that of HIV-1 V3.
Insights
Mutating the V3 loop of simian immunodeficiency virus (SIVmac) env gene shows this region is tolerant to change, with most mutants retaining replication ability. Some changes impacted virus entry and cell tropism.
Area of Science:
- Virology
- Molecular Biology
- Immunology
Background:
- The V3 loop of the human immunodeficiency virus type 1 (HIV-1) envelope (env) protein is critical for viral infectivity and tropism.
- Understanding the functional role of analogous regions in simian immunodeficiency virus (SIV) is crucial for comparative virology and vaccine development.
Purpose of the Study:
- To investigate the functional significance of the SIVmac V3 loop by creating and analyzing various mutant forms.
- To determine the impact of specific amino acid changes within the SIVmac V3 loop on viral replication and cell tropism.
Main Methods:
- Generation of 31 distinct SIVmac env mutants with single to quadruple amino acid substitutions in the V3 loop.
- Assessment of viral replication kinetics in three distinct cell types: CEMx174 cells, rhesus monkey peripheral blood mononuclear cells, and rhesus monkey alveolar macrophages.
Main Results:
- Twenty-two out of 31 SIVmac V3 loop mutants replicated in at least one cell type, indicating significant tolerance to amino acid alterations in this region.
- Ten mutants exhibited replication kinetics comparable to wild-type virus across all tested cell lines.
- Nine mutants showed impaired or absent replication, with some linked to inefficient gp160 precursor processing and altered virus entry or cell tropism.
Conclusions:
- The SIVmac V3 loop region is remarkably tolerant to amino acid substitutions, with many mutants maintaining replication competence.
- Specific mutations within the SIVmac V3 loop can differentially affect viral replication in various cell types and impact virus entry and tropism, mirroring functions observed in HIV-1 V3.