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Glycosylation is necessary for the correct folding of human immunodeficiency virus gp120 in CD4 binding

Y Li1, L Luo, N Rasool

  • 1Department of Microbiology and Immunology, Faculty of Medicine, University of Ottawa, Ontario, Canada.

Journal of Virology
|January 1, 1993
PubMed

Insights

Carbohydrate chains on the human immunodeficiency virus (HIV) envelope glycoprotein gp120 are not essential for CD4 receptor binding. However, N-linked glycosylation is crucial for gp120 to achieve the correct conformation for binding.

Area of Science:

  • Virology
  • Immunology
  • Glycobiology

Background:

  • The role of carbohydrate moieties on the human immunodeficiency virus (HIV) envelope glycoprotein gp120 in CD4 receptor binding remains controversial.
  • Previous studies have yielded conflicting results regarding the necessity of glycosylation for gp120-CD4 interactions.

Purpose of the Study:

  • To investigate the specific role of carbohydrate on HIV gp120 in mediating binding to the CD4 receptor.
  • To determine whether glycosylation is required for the proper conformation of gp120 for CD4 interaction.

Main Methods:

  • Comparison of CD4 binding activity of glycosylated, deglycosylated, and nonglycosylated forms of HIV-1 and HIV-2 gp120.
  • Generation of nonglycosylated gp120 via signal sequence deletion or tunicamycin synthesis.
  • Enzymatic deglycosylation using endoglycosidase H or endoglycosidase F/N glycanase.
  • Assessing gp120 conformation through its ability to bind CD4.

Main Results:

  • Nonglycosylated gp120 variants failed to bind to CD4, indicating a requirement for glycosylation in the binding process.
  • Highly mannosylated gp120 demonstrated robust binding to soluble CD4 molecules.
  • Enzymatic removal of carbohydrate chains from already glycosylated gp120 did not impair CD4 binding.
  • These findings suggest that while carbohydrate chains themselves are not directly involved in the interaction, N-linked glycosylation is vital for establishing the correct gp120 conformation.

Conclusions:

  • Carbohydrate chains on HIV gp120 are not directly required for the interaction with the CD4 receptor.
  • N-linked glycosylation is essential for the proper folding and conformation of gp120, enabling the formation of a functional CD4-binding site.
  • This research clarifies the specific contribution of glycosylation to HIV-1 and HIV-2 gp120-CD4 binding dynamics.

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