Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.23.16 (HIV-1 protease)
 2,107 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Human immunodeficiency virus-1 (HIV-1) protease is catalytically active as a dimer of identical subunits that associate through noncovalent interactions. To investigate the forces stabilizing HIV-1 protease in its active form, we have studied the effects of pH and salts on structure and function of the enzyme. Enzymatic activity was measured by following the hydrolysis of a fluorogenic substrate. Dissociation of the dimer into its subunits was monitored by gel filtration, while conformational changes in the enzyme were probed by measurements of intrinsic tryptophan fluorescence. Mg2+ ions were capable of dissociating the dimeric enzyme with a concomitant red shift and increase in quantum yield of the tryptophan fluorescence, indicating increased accessibility of tryptophan to the aqueous environment. These structural changes also were associated with a loss of catalytic activity which was insensitive to substrate concentration, consistent with noncompetitive inhibition. Both structural and functional changes could be attributed to binding of Mg2+ ions to a site with an apparent dissociation constant of approximately 2 M. In contrast, increasing concentrations of Na ions up to 5 M were without effect. Increasing pH had similar effects on HIV-1 protease as increasing Mg2+ ions concentration, with concomitant dissociation into subunits, increase in quantum yield and red shift in tryptophan fluorescence, and loss in catalytic activity. The apparent pKa for these structural and functional transitions was 6.95 +/- 0.08. This value is consistent with that of an aspartic acid residue with an anomalously high pKa, which has been implicated in the catalytic activity of HIV-1 protease.
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PMID:Effect of pH and nonphysiological salt concentrations on human immunodeficiency virus-1 protease dimerization. 784 Sep 36

Recently we demonstrated that the p58 subunit of p68/p58 HIV-2 reverse transcriptase (RT) heterodimer, produced by processing of p68/p68 homodimer with recombinant HIV-2 protease, terminates at Met484 [Fan, N., et al. (1995) J. Biol. Chem. 270, 13573-13579]. Here we describe purification and characterization of the p68/p58 heterodimer of recombinant HIV-2 RT. It exhibited both RT and RNase H activities, obeyed Michaelis-Menten kinetics, and was competitively inhibited by the DNA chain terminator ddTTP (Ki[app] = 305 +/- 20 nM). The HIV-2 RT-associated RNase H exhibited a marked preference for RNA hydrolysis from a HIV-1 gag-based heteropolymeric RNA/DNA hybrid in the presence of either Mg2+ or Mn2+, compared to the [3H]poly(rA).poly(dT) or [3H]poly(rG).poly(dC) homopolymeric substrates. Relative to HIV-1 RT, the RNase H activity of HIV-2 RT was only 5% toward the [3H]poly(rA).poly(dT) in the presence of Mg2+. The size distribution of products generated from [3H]poly(rA).poly(dT) by HIV-2 RT-associated RNase H was markedly distinct from that of HIV-1 RT in the presence of Mg2+ or Mn2+. The p68/p58 HIV-2 RT heterodimer, produced by specific cleavage using HIV-2 protease, should be useful for inhibition and biophysical studies aimed at discovering and designing drugs directed toward HIV-2.
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PMID:Characterization of the p68/p58 heterodimer of human immunodeficiency virus type 2 reverse transcriptase. 863 74