CXCR4 (Formerly Fusin) Is Chemokine Co-Receptor for HIV
In new studies of the binding of HIV to T cells of the immune system, researchers have renamed the co-receptor formally called fusin. Past studies have shown that HIV's surface protein, gp120, attaches to a CD4 receptor on a T cell. A second coreceptor, which normally binds chemokines, is then required for the entry of HIV into the T cell. Strains of HIV that act early in infection use a receptor called CCR5, and strains of HIV that act later on in infections use fusin, or CXCR4, as it is now called.

Researchers agree that after gp120 on HIV binds to the CD4 receptor, HIV goes through a conformational change that allows it to bind to the chemokine receptor. CXCR4 investigators speculate that after the conformational change, the chemokine receptor passes the gp120-CD4 complex through the T cell membrane, while part of the HIV envelope protein, gp41, is then free pass the contents of the HIV virus into the T cell. The new discoveries are continuing to fuel research on devising ways to counter HIV, including the construction of antibodies that block chemokine receptors.

"Investigators Detail HIV's Fatal Handshake," Science vol. 274, page 502, October 25, 1996