Human immunodeficiency virus 1 protease expressed in Escherichia coli behaves as a dimeric aspartic protease (original) (raw)
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Retroviruses code for a specific protease which is essential for polyprotein precursor processing and viral infectivity. The HIV-specific protease has been predicted to be an aspartic protease which is located at the amino terminus of the pot gene. We have prepared several constructs for bacterial expression of the protease. Two of them span the whole protease region and result in its autocatalytic activation. Analysis of the dynamics of this activation indicates a two-step process which starts at the carboxy terminus and ends at the amino terminus of the protease. The activated protease is a molecule of 9 kd as evidenced by monoclonal antibody in immunoblot analysis. A construct in which the carboxy terminus of the protease is deleted results in a stable, enzymatically inactive 27-kd protein which proved useful as substrate since it contains one of the predicted cleavage sites. The stability of this protein indicates that the carboxy-terminal sequences of the protease are essential for its activity and its autocatalytic activation. The protease which is very hydrophobic was solubilized by acetone treatment and passaged over ultrogel and propylagarose columns for partial purification. It elutes as a dimer and tends to aggregate. It is inhibited by pepstatin A in agreement with its expected active site and its theoretical classification as aspartic protease. Cleavage of the gag precursor results in the mature capsid protein, p17. The protease does not, however, cleave the denatured 27-kd substrate or the denatured gag precursor. Therefore its specificity appears to be not solely sequence- but also conformationdependent . This property needs to be taken into account for the development of protease inhibitors for therapy of AIDS.
The EMBO Journal
Communicated by K.Moelling Retroviruses code for a specific protease which is essential for polyprotein precursor processing and viral infectivity. The HIV-specific protease has been predicted to be an aspartic protease which is located at the amino terminus of the pot gene. We have prepared several constructs for bacterial expression of the protease. Two of them span the whole protease region and result in its autocatalytic activation. Analysis of the dynamics of this activation indicates a two-step process which starts at the carboxy terminus and ends at the amino terminus of the protease. The activated protease is a molecule of 9 kd as evidenced by monoclonal antibody in immunoblot analysis. A construct in which the carboxy terminus of the protease is deleted results in a stable, enzymatically inactive 27-kd protein which proved useful as substrate since it contains one of the predicted cleavage sites. The stability of this protein indicates that the carboxy-terminal sequences of the protease are essential for its activity and its autocatalytic activation. The protease which is very hydrophobic was solubilized by acetone treatment and passaged over ultrogel and propylagarose columns for partial purification. It elutes as a dimer and tends to aggregate. It is inhibited by pepstatin A in agreement with its expected active site and its theoretical classification as aspartic protease. Cleavage of the gag precursor results in the mature capsid protein, p17. The protease does not, however, cleave the denatured 27-kd substrate or the denatured gag precursor. Therefore its specificity appears to be not solely sequence-but also conformationdependent. This property needs to be taken into account for the development of protease inhibitors for therapy of AIDS.
Active human immunodeficiency virus protease is required for viral infectivity
Proceedings of the …, 1988
Retroviral proteins are synthesized as polyprotein precursors that undergo proteolytic cleavages to yield the mature viral proteins. The role of the human immunodeficiency virus (HIV) protease in the viral replication cycle was examined by use of a site-directed mutation in the protease gene. The HIV protease gene product was expressed in Escherichia coHl and observed to cleave HIV gag p55 to gag p24 and gag p17 in vitro. Substitution of aspartic acid residue 25 (Asp-25) of this protein with an asparagine residue did not affect the expression of the protein, but it eliminated detectable in vitro proteolytic activity against HIV gag p55. A mutant HIV provirus was constructed that contained the Asn-25 mutation within the protease gene. SW480 human colon carcinoma cells transfected with the Asn-25 mutant proviral DNA produced virions that contained gag p55 but not gag p24, whereas virions from cells transfected with the wild-type DNA contained both gag p55 and gag p24. The mutant virions were not able to infect MT-4 lymphoid cells. In contrast, these cells were highly sensitive to infection by the wild-type virions. These results demonstrate that the HIV protease is an essential viral enzyme and, consequently, an attractive target for anti-HIV drugs.
Proceedings of the National Academy of Sciences, 1995
Production of infectious human immunodeficiency virus (HIV) requires proper polyprotein processing by the dimeric viral protease. The trans-dominant inhibitory activity of a defective protease monomer with the active site Asp-25 changed to Asn was measured by transient transfection. A proviral plasmid that included the drug-selectable Escherichia coli gpt gene was used to deliver the wild-type (wt) or mutant proteases to cultured cells. Coexpression of the wt proviral DNA (HIV-gpt) with increasing amounts of the mutant proviral DNA (HIV-gpt D25N) results in a concomitant decrease in proteolytic activity monitored by in vivo viral polyprotein processing. The viral particles resulting from inactivation of the protease were mostly immature, consisting Abbreviations: HIV, human immunodeficiency virus; wt, wild type.
Biochemistry, 2000
Aspartates 25 and 125, the active site residues of HIV-1 protease, participate functionally in proteolysis by what is believed to be a general acid-general base mechanism. However, the structural role that these residues may play in the formation and maintenance of the neighboring S1/S1′ substrate binding pockets remains largely unstudied. Because the active site aspartic acids are essential for catalysis, alteration of these residues to any other naturally occurring amino acid by conventional site-directed mutagenesis renders the protease inactive, and hence impossible to characterize functionally. To investigate whether Asp-25 and Asp-125 may also play a structural role that influences substrate processing, a series of active site protease mutants has been produced in a cell-free protein synthesizing system via readthrough of mRNA nonsense (UAG) codons by chemically misacylated suppressor tRNAs. The suppressor tRNAs were activated with the unnatural aspartic acid analogues erythro--methylaspartic acid, threo-methylaspartic acid, or , -dimethylaspartic acid. On the basis of the specific activity measurements of the mutants that were produced, the introduction of the -methyl moiety was found to alter protease function to varying extents depending upon its orientation. While a -methyl group in the erythro orientation was the least deleterious to the specific activity of the protease, a -methyl group in the threo orientation, present in the modified proteins containing threo--methylaspartate and , -dimethylaspartate, resulted in specific activities between 0 and 45% of that of the wild type depending upon the substrate and the substituted active site position. Titration studies of pH versus specific activity and inactivation studies, using an aspartyl protease specific suicide inhibitor, demonstrated that the mutant proteases maintained bell-shaped pH profiles, as well as suicide-inhibitor susceptibilities that are characteristic of aspartyl proteases. A molecular dynamics simulation of the -substituted aspartates in position 25 of HIV-1 protease indicated that the threo--methyl moiety may partially obstruct the adjacent S1′ binding pocket, and also cause reorganization within the pocket, especially with regard to residues Val-82 and Ile-84. This finding, in conjunction with the biochemical studies, suggests that the active site aspartate residues are in proximity to the S1/S1′ binding pocket and may be spatially influenced by the residues presented in these pockets upon substrate binding. It thus seems possible that the catalytic residues cooperatively interact with the residues that constitute the S1/S1′ binding pockets and can be repositioned during substrate binding to orient the active site carboxylates with respect to the scissile amide bond, a process that likely affects the facility of proteolysis.
The Journal of biological chemistry, 1993
Autoproteolysis of the retroviral aspartyl proteases is a major obstacle to purification and analysis of these enzymes. A mutagenic approach to rendering autolytic cleavage sites less labile was applied to the primary cleavage site between Leu5 and Trp6 in human immunodeficiency virus-1 (HIV-1) protease. From predictions based on known substrates it was concluded that amino acids Lys or Ser in place of Gln at position 7 would prevent cleavage at the Leu5-Trp6 peptide bond, therefore stabilizing the protein. Autoproteolytic stability was enhanced at least 100-fold by these mutations. At longer time points the protease was degraded at secondary sites which contained adequate substrate sequences but were conformationally restricted. Conversely, a mutation in HIV-2 protease which changed Lys7 to Gln rendered the protein 3-fold less stable and shifted the position of the initial autoproteolytic cleavage from Phe3-Ser4 to Leu5-Trp6. The effects of these mutations demonstrate that small ch...
Biochemistry, 1993
A variant of the simian immunodeficiency virus protease (SIV PR), covalently bound to the inhibitor 1,2-epoxy-3-(p-nitrophenoxy)propane (EPNP), was crystallized. The structure of the inhibited complex was determined by X-ray crystallography to a resolution of 2.4 A and refined to an R factor of 19%. The variant, SIV PR S4H, was shown to diminish the rate of autolysis by at least 4-fold without affecting enzymatic parameters. The overall root mean square (rms) deviation of the a-carbons from the structure of HIV-1PR complexed with a peptidomimetic inhibitor (7HVP) was 1.16 A. The major differences are concentrated in three surface loops with rms differences between 1.2 and 2.1 A. For 60% of the molecule the rms deviation was only 0.6 A. The structure reveals one molecule of EPNP bound per protease dimer, a stoichiometry confirmed by mass spectral analysis. The epoxide moiety forms a covalent bond with either of the active site aspartic acids of the dimer, and the phenyl moiety occupies the P1 binding site. The EPNP nitro group interacts with Arg 8. This structure suggests a starting template for the design of nonpeptidebased irreversible inhibitors of the SIV and related HIV-1 and HIV-2 PRs. Simian immunodeficiency virus (SIV) * is a retrovirus closely related to the type 2 human immunodeficiency virus (HIV-2) and more distantly related to human immunodeficiency virus type 1 (HIV-1). Infectious clones of a strain isolated from macaque monkeys (SIVmac239) also produce an AIDS-like diseaseinrhesusmonkeys (Kestler et al., 1990). Theseinfected monkeys provide an animal model for testing therapeutic agents targeting HIV-1 or HIV-2. The structure of SIVmaC protease (SIV PR) was determined to facilitate the incorporation of data from in vivo testing with efforts to improve the design of drugs targeting the HIV-2 and HIV-1 PRs. The residues in the binding pocket of SIV PR differ from those of HIV-1 PR in 3 of 13 positions identified as major peptide binding determinants in HIV-1 PR (Miller et al., 1989). Despite these differences, SIV PR is capable of authentically processing the HIV-1 p53gag polyprotein in vitro (Grant et al., 1991). The sequence of HIV-2 PR is identical to SIV PR at these 13 positions. It has been shown in uivo that thevirus can develop resistance to drugs targeting reverse transcriptase (Richman, 1993). It has been proposed that the virus could develop resistance to antiprotease drugs as well (Cameron et al., 1993). A comparison of the HIV-1, HIV-2, and SIV protease structures will identify regions that are structurally conserved and may
Proceedings of the National Academy of Sciences, 1987
The mature gag and pol proteins of human immunodeficiency virus (HIV) and all retroviruses derive from large gag and gag-pol polyprotein precursors by posttranslational cleavage. A highly specific, virally encoded protease is required for this essential proteolytic processing. In this study, the HIV protease gene product was expressed in Escherichia coli and shown to autocatalyze its maturation from a larger precursor. In addition, this bacterially produced HIV protease specifically processed an HIV p55 gag polyprotein precursor when coexpressed in E. coli. This system will allow detailed structure-function analysis of the HIV protease and provides a simple assay for the development of potential therapeutic agents directed against this critical viral enzyme.
Acta Crystallographica Section D-biological Crystallography, 2010
The crystal structure of the unbound form of HIV-1 subtype A protease (PR) has been determined to 1.7 Å resolution and refined as a homodimer in the hexagonal space group P6 1 to an R cryst of 20.5%. The structure is similar in overall shape and fold to the previously determined subtype B, C and F PRs. The major differences lie in the conformation of the flap region. The flaps in the crystal structures of the unbound subtype B and C PRs, which were crystallized in tetragonal space groups, are either semi-open or wide open. In the present structure of subtype A PR the flaps are found in the closed position, a conformation that would be more anticipated in the structure of HIV protease complexed with an inhibitor. The amino-acid differences between the subtypes and their respective crystal space groups are discussed in terms of the differences in the flap conformations.