Question

Binding of gp120 causes:

• A. Infection of target cell
• B. Facilitation of co-receptor
• C. Fusing of virus and target cell
• D. None

Hint:

gp120 binds CD4 first, then exposes the site that engages CCR5 or CXCR4.

Answer 1

The Correct Option is B

Step 1: This question is about the HIV entry process. The HIV envelope has two glycoproteins, gp120 (surface) and gp41 (transmembrane), which work in sequence to allow the virus to enter a CD4 positive cell.

Step 2: gp120 first binds the CD4 receptor on the target cell. This binding triggers a conformational change in gp120 that exposes and engages the co-receptor (CCR5 or CXCR4). So the immediate effect of gp120 binding is facilitation of co-receptor engagement. This makes option b correct.

Step 3: The actual fusion of the viral envelope with the cell membrane is carried out by gp41, not gp120, so option c is wrong. Infection of the target cell is the final outcome of the entire entry and replication cascade and not the direct result of gp120 binding alone, so option a is not the best single answer.

Step 4: Hence gp120 binding leads to facilitation of co-receptor binding.