Hiv-1 Gp120 Envelope Glycoprotein Complexed With CD4 Antigen 

The HIV gp120 interacts with the CD4 antigen of a T4 lymphocyte in the structure at the right. It is also shown bound to a neutralizing antibody (17b). At present a wire frame image of the structure of the proteins is shown. You can revert to the original image using the reload button of your browser and can make changes in the structure using the buttons in the text or table below.

This structure shows the extracellular part of HIV gp120 (dark blue) bound to the extracellular part of CD4 antigen (light blue) which is located on the surface of a T lymphocyte or macrophage. Also shown is a neutralizing antibody against HIV gp120 (light chain in green and heavy chain in light green). You may want to turn the antibody chains off at this stage using these buttons:  Heavy chain off     Light chain off      Restore heavy chain wireframe      Restore light chain wireframe
The molecule can be rotated at any time by left clicking the mouse on the molecule and dragging the image with the left button depressed or you can switch on rotation here: Rotate On    Rotate Off 

Gp120-CD4 antigen interactions
The CD4 antigen on the cell surface and the gp120 of the virus interact via a depression in the gp120 molecule that lacks carbohydrate chains  (switch on carbohydrate space fill here). Direct contacts between the two proteins involve 22 CD4 amino acids and 26 gp120 amino acids but the residues that are most important in this association are trp 427, glu 370, gly 473  and ile 371 of gp120  (switch on red spacefill:    here) that interact with phe 43 of CD4 (switch on yellow spacefill:  here) and val 430 of gp120  (switch on red spacefill:  here) that interacts with arg 59 of CD4 (switch on yellow spacefill:  here). Look at the interaction by zooming here (return to original size:).  You can also space-fill the individual amino acids and the carbohydrate chains using the buttons in the table below.

Gp120-chemokine receptor interactions
Besides interacting with CD4 antigen on the surface of the T4 cell, gp120 must also interact with a co-receptor. There are many of these chemokine receptors that can interact with gp120. The binding site for the chemokine is induced after the CD4 antigen is bound. This site overlaps with the heavy chain of the antibody in this image (Switch on heavy chain space fill here). The gp120 residues involved in this interaction are lys121, arg419, lys 421 and gln422 (Switch on magenta space fill here). Notice again, that this interaction also is in a region that lacks carbohydrate chains  (switch on space fill here). You can also space-fill the individual amino acids using the buttons below.

Using the buttons below, change each of the chains to ribbons or space-fill to see, more clearly, how the peptides interact. 

Note that the gp120 molecule is heavily glycosylated (Space Fill on Spacefill Off ) but the CD4 molecule binds into a non-glycosylated pocket in the gp120 (Spacefill the CD4 molecule here  ).

To return to the original wire-frame structure, use the reload/refresh button on your browser.

Further changes and selection may be made using the Chime menu. Right click on the molecule to show the Chime menu.

Protein database information is here   Get Chime here

You may now wish to use the reload button to go back to the page from which you entered this page. From there go to the Chime presentation that shows the domains of the gp120 molecule.

© Richard Hunt, University of South Carolina School of Medicine