Fig. 1

Schematic view of the early steps of HIV infection. The HIV envelope (Env), consisting of gp120 and gp41 subunits, first binds to the CD4 receptor located at the plasma membrane of the infected cell (1). This binding induces a conformational change in gp120 that allows the interaction of its V3 loop with a co-receptor (2). The co-receptor can be either CCR5 or CXCR4, defining the tropism of the virus (see main text). This second binding induces a new conformational change in gp120 which exposes the fusion peptide of gp41 that anchors its N-terminal domain into the plasma membrane of the target cell (3). This initiates a process of fusion that will lead to the release of the viral content into the cytoplasm of the infected cell (for more details see [38, 54])