HIV gp41 is a glycoprotein subunit that remains non-covalently-bound to gp120, and provides the second step by which HIV enters the cell. It is originally buried within the viral envelope, but, when gp120 binds to a CD4, gp120 changes its conformation, causing gp41 to become exposed, where it can assist in fusion with the host cell. The Env gene does not, in fact, code for gp120 and gp41, but for a precursor to both, gp160. During HIV reproduction, the host cell's own enzymes cleave gp160 into gp120 and gp41. Alternative Names: SU antigen, Glycoprotein 41 antigen, gp41 antigen, HIV-1 gp41, Envelope surface glycoprotein gp41 antigen, HIV 1 gp41 protein, HIV1 gp41, HIV-1 gp41 antigen, Surface protein antigen, gp41 antigen, HIV 1 gp41 antigen, HIV-1 gp41 protein, HIV 1 gp41, gp41 glycoprotein antigen, Human Immunodeficiency Virus 1 antigen