gp120 
(jē′pē′wən-twĕntē)
(jē′pē′wən-twĕntē)n.
A glycoprotein that protrudes from the surface of the HIV virus and binds to the glycoprotein CD4 in human cells.
[g(lyco)p(rotein) 120 (from its apparent molecular mass of 120 kilodaltons as extrapolated from its mobility during electrophoresis).]