Mechanism of Viral Entry/Membrane Fusion macrophage 1. Initial interaction between gp120 and CD4.
2. Conformational change in gp120 allows for secondary interaction with CCR5. 
3. The distal tips of gp41 are inserted in to the cellular membrane.

 4. gp41 undergoes significant conformational change; folding in half and forming coiled-coils. This process pulls the viral and cellular membranes together, fusing them.
Own work
Mike Jones original. Modification by Rasbak