The HIV-1 Nucleocapsid Regulates Its Own Condensation by Phase-Separated Activity-Enhancing Sequestration of the Viral Protease during Maturation.

A growing number of studies indicate that mRNAs and long ncRNAs can affect protein populations by assembling dynamic ribonucleoprotein (RNP) granules. These phase-separated molecular 'sponges', stabilized by quinary (transient and weak) interactions, control proteins involved in numerous biological functions. Retroviruses such as HIV-1 form by self-assembly when their genomic RNA (gRNA) traps Gag and GagPol polyprotein precursors. Infectivity requires extracellular budding of the particle followed by maturation, an ordered processing of ∼2400 Gag and ∼120 GagPol by the viral protease (PR). This leads to a condensed gRNA-NCp7 nucleocapsid and a CAp24-self-assembled capsid surrounding the RNP. The choreography by which all of these components dynamically interact during virus maturation is one of the missing milestones to fully depict the HIV life cycle. Here, we describe how HIV-1 has evolved a dynamic RNP granule with successive weak-strong-moderate quinary NC-gRNA networks during the sequential processing of the GagNC domain. We also reveal two palindromic RNA-binding triads on NC, KxxFxxQ and QxxFxxK, that provide quinary NC-gRNA interactions. Consequently, the nucleocapsid complex appears properly aggregated for capsid reassembly and reverse transcription, mandatory processes for viral infectivity. We show that PR is sequestered within this RNP and drives its maturation/condensation within minutes, this process being most effective at the end of budding. We anticipate such findings will stimulate further investigations of quinary interactions and emergent mechanisms in crowded environments throughout the wide and growing array of RNP granules.

Bisbenzimidazole derivatives as potent inhibitors of the trypsin-like sites of the immunoproteasome core particle.

In this study, a monomeric (MB) and a dimeric (DB) bisbenzimidazoles were identified as novel proteasome inhibitors of the trypsin-like activity located on ß2c sites of the constitutive 20S proteasome (IC50 values at 2-4 µM range). Remarkably, they were further shown to be 100- and 200-fold more potent inhibitors of the immunoproteasome trypsin-like activity (ß2i sites, IC50=24 nM) than of the homologous constitutive activity. Molecular models of inhibitor/enzyme complexes in the two types of trypsin-like sites and corresponding computed binding energy values corroborated kinetic data. Different binding modes were suggested for MB and DB to the ß2c and ß2i trypsic sites. Each pointed to better contacts of the ligand inside the ß2i active site than for ß2c site. MB and DB represent the first selective inhibitors of the immunoproteasome trypsin-like activity described to date and can be considered as prototypes for inhibiting this activity.

New C(4)- and C(1)-derivatives of furo[3,4-c]pyridine-3-ones and related compounds: evidence for site-specific inhibition of the constitutive proteasome and its immunoisoform.

A set of 18 new C(4) and C(1) derivatives of nor-cerpegin (1,1-dimethyl furo[3,4-c]pyridine-3-one), 6 model compounds (γ- and δ-lactones) and 20 furo- or thieno[2,3-d]-pyrimidine-4-one related compounds were designed and synthesized. Each compound was assayed for inhibition of CT-L, T-L and PA proteolytic activities of 20S constitutive proteasome (c20S). Most performant compounds were also assayed on 20S immunoproteasome (i20S). Compound 10 with a benzylamino group at C(4) and dimethylated at C(1) of the furopyridine ring was the most efficient PA site-specific inhibitor of the c20S (IC50(cPA) of 600nM) without noticeable inhibition of the i20S PA site (iPA). In silico docking assays for 10 at the iPA catalytic site revealed the absence of poses normally observed for this compound and related ones at the constitutive PA site (cPA). The thieno[2,3-d]pyrimidine-4-one 40 was T-L site-specific with a mild inhibition of both c20S and i20S in vitro (IC50(cT-L) of 9.9µM and IC50(iT-L) of 6.7µM). In silico docking assays of 40 at T-L sites of c20S and i20S revealed almost identical first rank poses in the two types of sites with no possibility left for nucleophilic attack by Thr1 as observed for the fused furopyridine-3-one 10.

α- and ß-hydrazino acid-based pseudopeptides inhibit the chymotrypsin-like activity of the eukaryotic 20S proteasome.

We describe the synthesis of a library of new pseudopeptides and their inhibitory activity of the rabbit 20S proteasome chymotrypsin-like (ChT-L) activity. We replaced a natural α-amino acid by an α- or a ß-hydrazino acid and obtained inhibitors of proteasome up to a submicromolar range (0.7 µM for molecule 24b). Structural variations influenced the inhibition of the ChT-L activity. Models of inhibitor/20S proteasome complexes corroborated the inhibition efficacies obtained by kinetic studies.

Dimerized linear mimics of a natural cyclopeptide (TMC-95A) are potent noncovalent inhibitors of the eukaryotic 20S proteasome.

Noncovalent proteasome inhibitors introduce an alternative mechanism of inhibition to that of covalent inhibitors used in cancer therapy. Starting from a noncovalent linear mimic of TMC-95A, a series of dimerized inhibitors using polyaminohexanoic acid spacers has been designed and optimized to target simultaneously two of the six active sites of the eukaryotic 20S proteasome. The homodimerized compounds actively inhibited chymotrypsin-like (Ki = 6-11 nM) and trypsin-like activities, whereas postacid activity was poorly modified. The noncovalent binding mode was ascertained by X-ray crystallography of the inhibitors complexed with the yeast 20S proteasome. The inhibition of proteasomal activities in human cells was evaluated. The use of the multivalency inhibitor concept has produced highly efficient and selective noncovalent compounds (no inhibition of calpain and cathepsin) that have potential therapeutic advantages compared to covalent binders such as bortezomib and carfilzomib.

Carbonylhydrazide-based molecular tongs inhibit wild-type and mutated HIV-1 protease dimerization.

We have designed and synthesized new molecular tongs based on a rigid naphthalene scaffold and evaluated their antidimer activity on HIV-1 protease (PR). We inserted carbonylhydrazide and oligohydrazide (azatide) fragments into their peptidomimetic arms to reduce hydrophobicity and increase metabolic stability. These fragments are designed to disrupt the protein-protein interactions by reproducing the hydrogen bond pattern found in the antiparallel ß-sheet formed between the N- and C-ends of the two monomers in the native PR. Kinetic analyses and fluorescent probe binding studies showed that several molecular tongs can inhibit PR dimerization. The best nonpeptidic molecular tongs to date were obtained with an inhibition constant K(id) of 50 nM for PR and 80 nM for the multimutated protease ANAM-11. The PR inhibition was selective, the aspartic proteases renin and pepsin were not inhibited.

Toward the first nonpeptidic molecular tong inhibitor of wild-type and mutated HIV-1 protease dimerization.

Herein we describe the synthesis and HIV-1 protease (PR) inhibitory activity of 16 new peptidomimetic molecular tongs with a naphthalene scaffold. Their peptidic character was progressively decreased. Two of these molecules exhibited the best dimerization inhibition activity toward HIV-1 wild-type and multimutated ANAM-11 proteases obtained to date for this class of molecules (∼40 nM for wild-type PR and 100 nM for ANAM-11 PR). Although the peptidic character of one molecular tong was completely suppressed, the mechanism of inhibition and inhibitory potency toward both proteases were maintained.

Dimer disruption and monomer sequestration by alkyl tripeptides are successful strategies for inhibiting wild-type and multidrug-resistant mutated HIV-1 proteases.

Wild-type and drug-resistant mutated HIV-1 proteases are active as dimers. This work describes the inhibition of their dimerization by a new series of alkyl tripeptides that target the four-stranded antiparallel beta-sheet formed by the interdigitation of the N- and C-monomer ends of each monomer. Analytical ultracentrifugation was used to give experimental evidence of their mode of action that is disruption of the active homodimer with formation of inactive monomer-inhibitor complexes. The minimum length of the alkyl chain needed to inhibit dimerization was established. Sequence variations led to a most potent HIV-PR dimerization inhibitor: palmitoyl-Leu-Glu-Tyr (Kid = 0.3 nM). Insertion of d-amino acids at the first two positions of the peptide moiety increased the inhibitor resistance to proteolysis without abolishing the inhibitory effect. Molecular dynamics simulations of the inhibitor series complexed with wild-type and mutated HIV-PR monomers corroborated the kinetic data. They suggested that the lipopeptide peptide moiety replaces the middle strand in the highly conserved intermolecular four-stranded beta-sheet formed by the peptide termini of each monomer, and the alkyl chain is tightly grasped by the active site groove capped by the beta-hairpin flap in a "superclosed" conformation. These new inhibitors were equally active in vitro against both wild-type and drug-resistant multimutated proteases, and the model suggested that the mutations in the monomer did not interfere with the inhibitor.