Question

HIV is the virus that causes AIDS. In the mid-1990s, researchers discovered an enzyme in HIV called protease. Once the enzyme's structure was known, researchers began looking for drugs that would fit into the active site and block it. If this strategy for stopping HIV infections were successful, it would be an example of what phenomenon?

Answer 1

HIV stands for Human Immunodeficiency Virus. As the name suggests, its host is human and it attacks the immune system rendering it weak. This disease is called Acquired Immunodeficiency Syndrome or famously known by its acronym which is AIDS. The disease weakens the immune system by attacking the T helper cells, which causes other opportunistic infections to arise. In most cases, the cause for the death of the patient suffering from AIDS is opportunistic infections like pneumonia and Candidiasis.

The protease is an enzyme that cleaves proteins and peptides into smaller fragments and amino acids. In the HIV life cycle, the genetic material is injected into the host and undergoes translation to produce large precursor proteins. The protease then cleaves these proteins into shorter fragments which will make up the coat proteins of the new viruses. If the protease is made inactive, the viruses would produce large precursor proteins that wouldn't be able to make it to coat proteins and hence the infection won't lead to viral multiplication and hence the disease.

Protease is an enzyme and just like other enzymes, it has a binding pocket for the substrate which is called the active site. If the researchers can block this active site with a drug, the drug would be called an antagonist. The binding of this drug would make the protein non-functional and hence inhibit its activity. The drug here will be competing with the substrate for the active site. This phenomenon is hence called competitive inhibition.

This method of inhibition is weak. Since the inhibitor would work only as long as its concentration is larger than the concentration of the substrate. Once the substrate concentration increases, the active site will be flooded with the substrate and the inhibitor would be rendered non-functional.