Reverse Transcriptase Inhibitors
HIV is a retrovirus. This means that the genetic material of the virus (RNA) gets copied into the DNA of the immune cells in the human body. In order for this to happen HIV uses a special protein called reverse transcriptase, which is responsible for inserting viral genes into the cellular DNA. As AidsEtc explains, this protein is one of the major targets for anti-HIV drugs. Some of these drugs (called nucleoside or nucleotide reverse transcriptase inhibitors or NRTIs) mimic genetic material and bind to the reverse transcriptase protein. When they do this, they stop this protein from copying viral genes into the host DNA. Other drugs do not resemble genetic material but still bind to the reverse transcriptase and block its activity.
Protease Inhibitors
When HIV is infecting human cells, it has a large protein that is, in essence, an amalgamation of many smaller viral proteins. For the virus to begin replicating, this large protein has to be broken back down into these functional subunits. This is done using an enzyme called a protease. As an article in the Journal of Leukocyte Biology explains, protease inhibitors are drugs that bind to the protease and inhibit its activity. Thus, by keeping the virus from assembling the machinery necessary to replicate inside of human cells, these drugs can slow the rate at which HIV infects the human body and depletes the immune system.
Fusion Inhibitors
For HIV to infect human immune cells, it has to be able to get into the cell. In order to do this, HIV binds to special proteins on the outside of these immune cells called receptors. HIV needs to bind to two different receptors, one of which is called CD4 and the other CCR-5. Fusion inhibitors are drugs that bind to the CCR-5 receptor and block it. If the virus cannot bind to both of these receptors, it cannot enter the cell and replicate.
