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Truncated variants of gp120 bind CD4 with high affinity and suggest a minimum CD4 binding region
S R Pollard1, M D Rosa, J J Rosa
1Biogen Inc., Cambridge, MA.
Insights
Researchers identified key regions of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein, gp120, essential for binding to CD4. A smaller gp120 variant (ENV59) retains CD4 binding and may serve as an immunogen.
Area of Science:
- Virology
- Immunology
- Structural Biology
Background:
- The envelope glycoprotein gp120 is crucial for HIV-1 entry by binding to the CD4 receptor on host cells.
- Understanding the structural determinants of gp120-CD4 interaction is vital for developing effective HIV-1 therapeutics and vaccines.
Purpose of the Study:
- To delineate the minimal structural requirements of gp120 for high-affinity CD4 binding.
- To assess the immunogenic potential of a truncated gp120 variant lacking non-essential regions.
Main Methods:
- Site-directed mutagenesis was employed to create deletion variants of gp120.
- CD4 binding affinity of the gp120 variants was measured.
- Immunoprecipitation assays were performed using polyclonal antibodies to assess antigenicity.
Main Results:
- Deletion of N- and C-terminal residues, along with V1, V2, and V3 variable regions, resulted in a 287-amino acid variant (ENV59) that retained high-affinity CD4 binding.
- The ENV59 variant showed reduced recognition by polyclonal antibodies, suggesting the loss of immunodominant epitopes.
- Complementing co-expressed gp120 fragments and a circularly permuted molecule also bound CD4, providing insights into gp120 structure.
Conclusions:
- A significant portion of gp120, including variable regions, is dispensable for CD4 binding.
- The truncated gp120 variant ENV59 may be a promising immunogen candidate for eliciting antibodies against conserved HIV-1 epitopes.
- The structural data suggest potential proximity of gp120 termini or unconstrained folding of the N-terminus.
Abstract:
The envelope glycoprotein, gp120, of human immunodeficiency virus type 1 (HIV-1) binds the cellular protein CD4 with high affinity. By deletion we show that 62 N- and 20 C-terminal residues along with the V1, V2 and V3 variable regions of gp 120 are unnecessary for CD4 binding. A 287 residue variant (ENV59), missing those 197 amino acids, binds to CD4 with high affinity. A polyclonal antibody failed to efficiently precipitate ENV59 which is consistent with the loss of immunodominant antigenic structures in the regions deleted. This suggests that ENV59 may have potential as an immunogen, able to elicit antibodies against more conserved regions of gp120. Additionally, complementing co-expressed gp120 fragments as well as a circularly permuted molecule bind CD4, and suggest either that the molecular termini are adjacent in the folded structure, or that an N-terminal region folds into the structure unconstrained by its method of attachment to the rest of the molecule.