Weasel asked what is protease?

In science there is actually some method to the madness. Generally the suffix -ase means to cleave or cut
so protease is an enzyme that cleaves (cuts) proteins (usually they are highly specific). DNAses cleave DNA, phospases cleave off phosphates etc. The body (and viruses and bacteria) often have several forms of a protein some active and some not. This is a way of regulating body processes. Think of it like you have to cut open a bag of frozen peas before you can cook them. The peas in the freezer are the same as the peas in the saucepan, but you have to somehow gain access to the peas. You do this by cutting open the bag. In the simplest terms, proteases cut away parts of proteins that protect the active site of the protein.

In the case of HIV in order for the virus that buds out of a cell to be infectious certain proteins must be cleaved to make the active form. The protease does this. If you treat a patient with protease inhibitors this prevents the viral protein from entering the active form and thus the newly formed virus is no longer infectious. The protease inhibitors used are specific for the HIV proteases and don't effect other proteases on the body, but like all other AIDS drugs the virus can mutate and become resistant to protease inhibitors.