Virion with CD4:gp120 bound to CCR5/CXCR4 Virion with gp41 exposed Conformational changes in gp120 exposes gp41 Authored: Morrow, MP, Bukrinsky, M, 2006-03-07 21:26:47 Edited: Gopinathrao, G, 2006-02-17 18:35:46 Pubmed2541505 Pubmed3629244 Pubmed8500173 Pubmed8612573 Reactome Database ID Release 43164500 Reactome, http://www.reactome.org ReactomeREACT_8003 Reviewed: Reeves, J, 2006-06-12 15:22:40 The HIV protein known as gp41 is a transmembrane protein which is considered the major mediator of fusion of extracellular virions to the target cells in the host. HIV gp120 and gp41 proteins form non-covalently linked oligomers on the surface of virions. The gp41 subunit of the oligomer is anchored in the viral membrane and contains a non-polar fusion peptide at its N-terminus. Upon CD4 and receptor binding, gp120 undergoes a second conformation change. The conformation change exposes gp41 which continues to mediate fusion of the viral envelope with the host plasma membrane. Electron microscopy and circular dichroism measurements of the gp41 protein suggest a rod-like conformation with a high alpha-helical content. Although some studies suggest that gp41must dissociate from gp120 in order to cause fusion between HIV envelope and the target cell plasma membrane, evidence on this point is not conclusive.