Ann Taylor/HIV Protease

Function

Human Immunodeficiency Virus (HIV) is the cause of Acquired Immunodeficiency Syndrome (AIDS). HIV synthesizes all of its proteins as one long chain. This long chain must be cut into individual component proteins. This hydrolysis reaction is catalyzed by . Since this isn't a process that is used for normal human proteins, it is a target for medications that treat HIV and AIDS.

Structure of HIV-1 Protease

The X-ray crystallography structure of HIV-1 protease^[1][2] reveals that it is composed of , each consisting of 99 amino acid residues. The subunits come together in such as way as to form a where they meet. This tunnel is important because this is where the long protein chain substrate binds to HIV protease. You may be wondering how a polyprotein makes its way into the tunnel, as the to let it in. The key is the two flexible flaps on the top of the tunnel that to enter the tunnel. The flaps , shifting from an open to a closed conformation to bind the target in an appropriate conformation for cleavage.

The of HIV protease is mostly beta strands in alternating directions to form a structure known as a . In this color scheme, the N terminus for each protein chain is blue, and moves through the rainbow of colors (light blue, green, yellow, and orange) to the C terminus, shown in red.

How HIV Protease works

HIV protease is categorized as an Aspartate Protease. This means that are required for its function. In HIV protease, one aspartic acid from each protein chain interact with the that cleaves the peptide bond.

How drugs inhibit HIV Protease

 (Invirase) was the first protease inhibitor approved by the FDA for the treatment of HIV. It inhibits HIV protease by , preventing the binding  of polyproteins. Its chemical structure mimics the tetrahedral intermediate of the hydrolytic reaction, thereby  .[3] Saquinavir is essentially an uncleavable ligand, as indicated by the  on binding saquinavir or a polypeptide.  Resistance to saquinavir is due to alterations in the HIV protease sequence, including the mutation of [4]. Drugs used to treat HIV infection that inhibit  include  (Crixivan),  (Norvir), Saquinavir, Tipranavir, Amprenavir (Agenerase), Atazanavir (Rayataz), Darunavir (Prezista), Fosamprenavir (Lexiva or Telzir), Lopinavir (Kaletra), Nelfinavir (Viracept) and  (Viracept).