[Show abstract][Hide abstract] ABSTRACT: All retroviral proteases belong to the family of aspartic proteases. They are active as homodimers, each unit contributing one catalytic aspartate to the active site dyad. An important feature of all aspartic proteases is a conserved complex scaffold of hydrogen bonds supporting the active site, called the "fireman's grip," which involves the hydroxyl groups of two threonine (serine) residues in the active site Asp-Thr(Ser)-Gly triplets. It was shown previously that the fireman's grip is indispensable for the dimer stability of HIV protease. The retroviral proteases harboring Ser in their active site triplet are less active and, under natural conditions, are expressed in higher enzyme/substrate ratio than those having Asp-Thr-Gly triplet. To analyze whether this observation can be attributed to the different influence of Thr or Ser on dimerization, we prepared two pairs of the wild-type and mutant proteases from HIV and myeloblastosis-associated virus harboring either Ser or Thr in their Asp-Thr(Ser)-Gly triplet. The equilibrium dimerization constants differed by an order of magnitude within the relevant pairs. The proteases with Thr in their active site triplets were found to be approximately 10 times more thermodynamically stable. The dimer association contributes to this difference more than does the dissociation. We propose that the fireman's grip might be important in the initial phases of dimer formation to help properly orientate the two subunits of a retroviral protease. The methyl group of threonine might contribute significantly to fixing such an intermediate conformation.
Protein Science 11/2003; 12(10):2173-82. · 2.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The human immunodeficiency virus type 1 (HIV-1) protease is essential for production of infectious virus and is therefore a major target for the development of drugs against AIDS. Cellular proteins are also cleaved by the protease, which explains its cytotoxic activity and the consequent failure to establish convenient cell-based protease assays. We have exploited this toxicity to develop a new protease assay that relies on transient expression of an artificial protease precursor harboring the green fluorescent protein (GFP-PR). The precursor is activated in vivo by autocatalytic cleavage, resulting in rapid elimination of protease-expressing cells. Treatment with therapeutic doses of HIV-1 protease inhibitors results in a dose-dependent accumulation of the fluorescent precursor that can be easily detected and quantified by flow cytometric and fluorimetric assays. The precursor provides a convenient and noninfectious model for high-throughput screenings of substances that can interfere with the activity of the protease in living cells.
Antimicrobial Agents and Chemotherapy 10/2001; 45(9):2616-22. · 4.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: HIV-1 proteinase represents a promising target for antiviral chemotherapy. We have designed, synthesized, and tested modular inhibitors combining an active-site inhibitor tethered to a structure targeted to the dimerization domain of the enzyme. At pH 5 the parent active site inhibitor, the equimolar mixture of active site and dimerization inhibitors, and the best compound from our series of modular inhibitors show the same inhibition activity. At neutral pH, however, the combination of the dimerization and active-site inhibitors shows a synergistic effect. Moreover, the modular inhibitor has an IC50 value 5x lower than the parent active site inhibitor and 2x lower than the equimolar mixture of the two parent inhibitors. The Lineweaver-Burk plot for modular inhibitors corresponds to a pattern for mixed type inhibition.
Biochemical and Biophysical Research Communications 06/1996; 222(1):38-43. · 2.28 Impact Factor