Replacement of the P1 Amino Acid of Human Immunodeficiency Virus Type 1 Gag Processing Sites Can Inhibit or Enhance the Rate of Cleavage by the Viral Protease

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114

The human immunodeficiency virus type 1 (HIV-1) protease (PR) makes five obligatory cleavages in the viral Gag polyprotein precursor. The cleavage events release the virion structural proteins from the precursor and allow the virion to undergo maturation to become infectious. The protease cleavage between the matrix protein (MA) domain and the adjacent capsid protein (CA) domain releases CA from the membrane-anchored MA and allows the N terminus of CA to refold into a structure that facilitates the formation of hexamer arrays that represent the structural unit of the capsid shell. In this study, we analyzed the extent to which each of the HIV-1 Gag processing sites must be cleaved by substituting the P1-position amino acid at each processing site with Ile. A mutation that blocks cleavage at the MA/CA processing site (Y132I) displayed a strong transdominant effect when tested in a phenotypic mixing strategy, inhibiting virion infectivity with a 50% inhibitory concentration of only 4% of the mutant relative to the wild type. This mutation is 10-to 20-fold more potent in phenotypic mixing than an inactivating mutation in the viral protease, the target of many successful inhibitors, and more potent than an inactivating mutation at any of the other Gag cleavage sites. The transdominant effect is manifested as the assembly of an aberrant virion core. Virus containing 20% of the Y132I mutant and 80% of the wild type (to assess the transdominant effect on infectivity) was blocked either before reverse transcription (RT) or at an early RT step. The ability of a small amount of the MA/CA fusion protein to poison the oligomeric assembly of infectious virus identifies an essential step in the complex process of virion formation and maturation. The effect of a small-molecule inhibitor that is able to block MA/CA cleavage even partially would be amplified by this transdominant negative effect on the highly orchestrated process of virion assembly.

Section: Resultsmentioning

confidence: 99%

A Strongly Transdominant Mutation in the Human Immunodeficiency Virus Type 1 gag Gene Defines an Achilles Heel in the Virus Life Cycle

Lee

Harris

Swanstrom

2009

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114

“…Peptide library screens find that the P2 site within NC-p1 is preferentially a Val (7). However, these substitutions are not seen in WT virus, implying that a more efficient and presumably premature cleavage of this site may be detrimental to viral maturation (19,26,36).…”

Section: Discussionmentioning

confidence: 99%

“…The amino acid sequence of this site, with an Asn at P1 and an Ala at P2, is also the least homologous compared with the other HIV-1 protease substrates sites, which have hydrophobic residues at P1 and branched residues at P2. If either P1 or P2 is replaced with Phe, Leu, Met, and Tyr or with Val, respectively, the site is cleaved more efficiently (36). Peptide library screens find that the P2 site within NC-p1 is preferentially a Val (7).…”

Section: Discussionmentioning

confidence: 99%

Structural Basis for Coevolution of a Human Immunodeficiency Virus Type 1 Nucleocapsid-p1 Cleavage Site with a V82A Drug-Resistant Mutation in Viral Protease

Prabu-Jeyabalan

Nalivaika

King

et al. 2004

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Maturation of human immunodeficiency virus (HIV) depends on the processing of Gag and Pol polyproteinsby the viral protease, making this enzyme a prime target for anti-HIV therapy. Among the protease substrates, the nucleocapsid-p1 (NC-p1) sequence is the least homologous, and its cleavage is the rate-determining step in viral maturation. In the other substrates of HIV-1 protease, P1 is usually either a hydrophobic or an aromatic residue, and P2 is usually a branched residue. NC-p1, however, contains Asn at P1 and Ala at P2. In response to the V82A drug-resistant protease mutation, the P2 alanine of NC-p1 mutates to valine (AP2V). To provide a structural rationale for HIV-1 protease binding to the NC-p1 cleavage site, we solved the crystal structures of inactive (D25N) WT and V82A HIV-1 proteases in complex with their respective WT and AP2V mutant NC-p1 substrates. Overall, the WT NC-p1 peptide binds HIV-1 protease less optimally than the AP2V mutant, as indicated by the presence of fewer hydrogen bonds and fewer van der Waals contacts. AlaP2 does not fill the P2 pocket completely; PheP1 makes van der Waals interactions with Val82 that are lost with the V82A protease mutation. This loss is compensated by the AP2V mutation, which reorients the peptide to a conformation more similar to that observed in other substrate-protease complexes. Thus, the mutant substrate not only binds the mutant protease more optimally but also reveals the interdependency between the P1 and P2 substrate sites. This structural interdependency results from coevolution of the substrate with the viral protease.Human immunodeficiency virus type 1 (HIV-1) matures after the viral protease processes (35) the Gag and Pol polyproteins at 10 substrate locations (3, 15). Therefore, inhibition of HIV-1 protease represents an important avenue for antiviral therapy (13, 48). The substrate sequences cleaved by the protease are nonhomologous (3), with the sequence of the nucleocapsid-p1 (NC-p1) substrate being the most different. In spite of the poor sequence homology among the substrate sites, a series of substrate-protease crystal structures led us to hypothesize that substrate specificity in HIV-1 protease results from the enzyme's recognizing an asymmetric shape (or envelope) rather than a particular amino acid sequence (40). This shape results from the conformation that a particular substrate sequence can adopt, implying that an interdependency necessarily exists among the different substrate residue sites.All of the protease inhibitors whose designs were structure based bind competitively (8,18,28,52,53) at the active site. Since these inhibitors bind at the same site as the substrates, many protease residues contact both substrates and inhibitors. Drug resistance, which often develops in the presence of therapeutic protease inhibitors, results from high viral turnover, the infidelity of the viral reverse transcriptase (16,42,43), and selective pressure on the virus. With drug resistance, the protease no longer binds as tightly to inhibitors but r...

“…Several studies have examined the order of cleavage for the different sites within the HIV-1 Gag precursor, and there is general agreement that the first cleavage occurs between the p2 spacer peptide and the NC protein (11,15,23,28,35,36,54). Intermediate cleavages occur at the MA/CA and p1/p6 sites (36,54).…”

mentioning

confidence: 99%

“…The relative rate of cleavage at different sites within the precursors has also been evaluated. Using a system in which the Gag precursor is processed by the addition of purified PR in trans, the rates of cleavage were determined to vary by as much as 400-fold between sites (35,36). Of note, this difference is much greater than that reported for the cleavage of peptides designed to reflect the sequence at the different sites (3,7,23,29,38,40,48).…”

mentioning

confidence: 99%

Ordered Processing of the Human Immunodeficiency Virus Type 1 GagPol Precursor Is Influenced by the Context of the Embedded Viral Protease

Pettit¹,

Clemente

Jeung

et al. 2005

Ordered and accurate processing of the human immunodeficiency virus type 1 (HIV-1) GagPol polyprotein precursor by a virally encoded protease is an indispensable step in the appropriate assembly of infectious viral particles. The HIV-1 protease (PR) is a 99-amino-acid enzyme that is translated as part of the GagPol precursor. Previously, we have demonstrated that the initial events in precursor processing are accomplished by the PR domain within GagPol in cis, before it is released from the polyprotein. Despite the critical role that ordered processing of the precursor plays in viral replication, the forces that define the order of cleavage remain poorly understood. Using an in vitro assay in which the full-length HIV-1 GagPol is processed by the embedded PR, we examined the effect of PR context (embedded within GagPol versus the mature 99-amino-acid enzyme) on precursor processing. Our data demonstrate that the PR domain within GagPol is constrained in its ability to cleave some of the processing sites in the precursor. Further, we find that this constraint is dependent upon the presence of a proline as the initial amino acid in the embedded PR; substitution of an alanine at this position produces enhanced cleavage at additional sites when the precursor is processed by the embedded, but not the mature, PR. Overall, our data support a model in which the selection of processing sites and the order of precursor processing are defined, at least in part, by the structure of GagPol itself.