Why might the knoblike proteins on the outer surface of hiv hold a key to the production of a vaccine against aids?

This is because the GP120 protein of the HIV virus that forms the ‘knob’ is essential for the infection of CD4 cells of the immune system by the virus. The glycoprotein is, therefore, a good target for vaccines especially since the molecule is highly conserved because most mutations in the region could be highly deleterious to the virus.