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Structural variability of env and gag gene products from a highly cytopathic strain of HIV-1
1INSERM U 322, Unit of Retrovirus and Associated Diseases, Marseille, France.
Abstract:
The glycoprotein precursor of the highly cytopathic Zairian virus HIV1-NDK synthesized in CEM leukemic cells displayed a molecular mass of 140 kDa (gp140) as compared to the 160 kDa of gp160 of HIV1-LAV prototype strain. This precursor was cleaved to produce a smaller than prototype extra-cellular envelope glycoprotein (gp100) and a transmembrane component with a usual size (gp41). Immunoprecipitates from tunicamycin-treated infected cells demonstrated the presence of a non-glycosylated precursor of 100 kDa for HIV1-LAV prototype strain and 90 kDa for HIV1-NDK. Digestion of labeled precipitates with a mixture of endoglycosidase F and glycopeptidase F reduced the size of HIV1-LAV gp160 and gp120 to 100 and 60 kDa, respectively, while HIV1-NDK gp140 and gp100, after treatment with the same enzymes, displayed an apparent molecular mass of 90 kDa and 55 kDa, respectively. From these data we conclude that HIV1-LAV gp120 and HIV1-NDK gp100 differ both in their proteic moiety (60 kDa and 55 kDa, respectively) and in their carbohydrate moiety (60 kDa and 45 kDa, respectively). These differences could not be deduced from the available gene sequences of the two viruses. A chimeric virus containing the first 124 amino acid residues of the envelope glycoprotein coded by HIV1-LAV sequence and the rest by HIV1-NDK displayed normal size envelope glycoproteins, demonstrating the involvement of this N-terminal sequence in the alteration of the molecular mass characteristic of HIV1-NDK gp140 and gp100. Finally, characterization of the gag gene products from both strains demonstrated that HIV1-NDK p18 and p15 have a slower electrophoretic mobility as compared to its HIV1-LAV counterparts. Therefore, structural properties of HIV1-NDK env and gag products, reflected by their unusual electrophoretic mobilities, may be responsible for HIV1-NDK biological properties.
Insights
Differences in human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins between the NDK and LAV strains were identified. These structural variations in HIV-1 NDK gp140 and gp100, impacting both protein and carbohydrate moieties, may explain its distinct biological properties.
Area of Science:
- Virology
- Molecular Biology
- Biochemistry
Background:
- Human immunodeficiency virus type 1 (HIV-1) exhibits genetic diversity, with different strains possessing unique structural and biological characteristics.
- The Zairian HIV-1 NDK strain shows higher cytopathic effects compared to the HIV-1 LAV prototype strain, suggesting underlying molecular differences.
Purpose of the Study:
- To investigate the molecular basis for the distinct properties of the HIV-1 NDK strain by analyzing its envelope (env) and gag gene products.
- To compare the structural characteristics of HIV-1 NDK glycoproteins with those of the HIV-1 LAV prototype strain.
Main Methods:
- Comparative analysis of molecular masses of glycoprotein precursors (gp160/gp140) and mature glycoproteins (gp120/gp100) using immunoprecipitation and tunicamycin treatment.
- Enzymatic digestion of glycoproteins with endoglycosidase F and glycopeptidase F to differentiate protein and carbohydrate components.
- Construction and analysis of a chimeric virus to identify the region responsible for altered glycoprotein size.
- Electrophoretic analysis of gag gene products (p18, p15).
Main Results:
- HIV-1 NDK gp140 precursor has a lower molecular mass (140 kDa) than HIV-1 LAV gp160 (160 kDa).
- HIV-1 NDK produced a smaller extracellular envelope glycoprotein (gp100) compared to HIV-1 LAV gp120.
- Enzymatic digestion revealed differences in both the protein and carbohydrate moieties of HIV-1 NDK gp100 and HIV-1 LAV gp120.
- The N-terminal 124 amino acid residues of the envelope glycoprotein were implicated in the altered molecular mass of HIV-1 NDK glycoproteins.
- HIV-1 NDK gag gene products (p18, p15) exhibited slower electrophoretic mobility than their HIV-1 LAV counterparts.
Conclusions:
- HIV-1 NDK and HIV-1 LAV strains possess distinct structural properties in their env and gag gene products.
- The observed differences in molecular mass and electrophoretic mobility of HIV-1 NDK proteins likely contribute to its unique biological characteristics and higher cytopathicity.