Polyprotein cleavage

Wiegers, K. Rutter, G. Kottler, H. Tessmer, U. Hohenberg, H. Krausslich, H. G. Sequential steps in human immunodeficiency virus particle maturation revealed by alterations of individual Gag polyprotein cleavage sites. J. Virol, 1998, 72 2846-2854. 

Grakoui, A., McCourt, D. W Wychowski, C., Feinstone, S. M., and Rice, C. M. (1993) Characterization of the hepatitis C virus-encoded serine proteinase determination of the proteinase-dependent polyprotein cleavage sites.. /. Virol. 67, 2832-2843. 

Ten protease inhibitors are currently on the market (see Figure 3.4). They all are competitive inhibitors of HIV PR (targeting the enzyme active site) and all but for one are peptidomimetics of the polyprotein cleavage sites. HIV Pis approved for clinical application are often referred to as first-generation and second-generation drugs. 

FIGURE 16.28 HIV mRNA provides the genetic information for synthesis of a polyprotein. Proteolytic cleavage of this polyprotein by HIV protease produces the individnal proteins required for viral growth and cellular infection. 

Rhinovirus, like poliovirus, synthesizes a large precursor protein from which all of the mature viral proteins are generated. Two viral proteases are involved in these cleavages 2A protease cleaves the polyprotein precursor at its own N terminus, while the 3C protease is responsible for additional cleavage events to generate the mature viral proteins. Both proteases can release themselves from the polyprotein precursor. Cleavage by 3C occurs between Gln/Gly, but flanking sequences affect efficiency (reviewed in Racaniello 2001). 

As an example, consider the genome of the hepatitis C virus. The genome codes for a single polyprotein that contains about 3010 amino acids. The polyprotein is subsequently cleaved into at least 10 proteins, including several which are structural components of the virus particle and several which are required, in one way or another, for the process of replication of the viral RNA or cleavage of the polyprotein itself into its functional units. 

Some of the peptides mentioned are overlapping in the POMC sequence. For example, additional cleavage of ACTH gives rise to a-MSH and corticotropin-like intermediary peptide (CLIP). Proteolytic degradation of p-LPH provides y-LPH and p-endorphin. The latter can be further broken down to yield met-enkephalin, while y-LPH can still give rise to p-MSH (not shown). Due to the numerous derivative products with biological activity that it has, POMC is also known as a polyprotein. Which end product is formed and in what amounts depends on the activity of the proteinases in the ER that catalyze the individual cleavages. 

Picornain 2A [EC 3.4.22.29] catalyzes the hydrolysis of peptide bonds including the selective cleavage of a particular peptide bond in the picornavirus polyprotein. Picornain 3C [EC 3.4.22.28] catalyzes the selective hydrolysis of the Gin—Gly bond in the poliovirus polyprotein. 

Pharmacology Saquinavir is an inhibitor of HIV protease which cleaves viral polyprotein precursors to generate functional proteins in HIV-infected cells. The cleavage of viral polyprotein precursors is essential for maturation of infectious virus. Saquinavir is a synthetic peptide-like substrate analog that inhibits the activity of HIV... 

Pharmacology Indinavir is an inhibitor of the HIV protease. HIV protease is an enzyme required for the proteolytic cleavage of the viral polyprotein precursors into the individual functional proteins found in infectious HIV. Indinavir binds to the protease active site and inhibits the activity of the enzyme. This inhibition prevents cleavage of the viral polyproteins resulting in the formation of immature... 

Pharmacology Nelfinavir is an inhibitor of the HIV-1 protease. Inhibition of the viral protease prevents cleavage of the gagpol polyprotein resulting in the production of immature, noninfectious virus. 

It is an inhibitor of the enzyme HIV protease which is required for the proteolytic cleavage of the viral polyprotein precursors into the individual functional proteins found in infectious HIV. 

Indinavir binds to the protease active site and inhibits the activity of the enzyme HIV protease preventing cleavage of the viral polyproteins resulting in the formation of immature noninfectious viral particles. 

Protease is responsible for cleaving these precursor molecules to produce the final structural proteins of the mature virion core. By preventing post-translational cleavage of the Gag-Pol polyprotein, protease inhibitors (Pis) prevent the processing of viral proteins into functional conformations, resulting in the production of immature, noninfectious viral particles (Figure 49-4). Protease inhibitors are active against both HIV-1 and HIV-2 unlike the NRTTs, however, they do not need intracellular activation. 

In the life cycle of HIV, its RNA is translated into a polypeptide chain that is composed of several individual proteins including protease, integrase and reverse transcriptase, but in this form these enzymes are not functional. They must be cleaved by viral proteases from the assembled sequence in order for them to become functional. These posttranslational modifications allow the enzymes to facilitate the production of new viruses. The protease itself is made up of two 99-amino-acid monomers, and an aspartic acid residue in the monomer is required for the cleavage. The protease inhibitors inhibit the enzyme protease and consequently interfere with viral replication and maturation by preventing proteases from cleaving proteins into peptides. In humans, these drugs inhibit cleavage of HIV gag and pol polyproteins, which are part of the essential viral structural components, P7, P9, P17 and P24, and... 

Darunavir is a nonpeptide second-generation protease inhibitor of HIV-1. In combination with ritonavir, it is superior to lopinavir plus ritonavir. Darunavir is a selective inhibitor of the cleavage of HIV-encoded gag-pol polyproteins in infected cells,... 

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