Characterization of a novel type of HIV-1 particle assembly inhibitor using a quantitative luciferase-Vpr packaging-based assay

Structure and Anti-HIV Activity of Betulinic Acid Analogues

Firstly discovered in 1980s, human immunodeficiency virus (HIV) continues to affect more and more people. However, there is no effective drug available for the therapy of HIV infection. Betulinic acid existing in various medicinal herbs and fruits exhibits multiple biological effects, especially its outstanding anti-HIV activity, which has drawn the attentions of many pharmacists. Among the derivatives of betulinic acid, some compounds exhibited inhibitory activities at the nanomolar concentration, and have entered phase II clinical trials. This paper summarizes the current investigations on the anti-HIV activity of betulinic acid analogues, and provides valuable data for subsequent researches.

Alpha-helicoidal HEAT-like Repeat Proteins (αRep) Selected as Interactors of HIV-1 Nucleocapsid Negatively Interfere with Viral Genome Packaging and Virus Maturation

A new generation of artificial proteins, derived from alpha-helicoidal HEAT-like repeat protein scaffolds (αRep), was previously characterized as an effective source of intracellular interfering proteins. In this work, a phage-displayed library of αRep was screened on a region of HIV-1 Gag polyprotein encompassing the C-terminal domain of the capsid, the SP1 linker and the nucleocapsid. This region is known to be essential for the late steps of HIV-1 life cycle, Gag oligomerization, viral genome packaging and the last cleavage step of Gag, leading to mature, infectious virions. Two strong αRep binders were isolated from the screen, αRep4E3 (32 kDa; 7 internal repeats) and αRep9A8 (28 kDa; 6 internal repeats). Their antiviral activity against HIV-1 was evaluated in VLP-producer cells and in human SupT1 cells challenged with HIV-1. Both αRep4E3 and αRep9A8 showed a modest but significant antiviral effects in all bioassays and cell systems tested. They did not prevent the proviral integration reaction, but negatively interfered with late steps of the HIV-1 life cycle: αRep4E3 blocked the viral genome packaging, whereas αRep9A8 altered both virus maturation and genome packaging. Interestingly, SupT1 cells stably expressing αRep9A8 acquired long-term resistance to HIV-1, implying that αRep proteins can act as antiviral restriction-like factors.

CD4-gp120 interaction interface - a gateway for HIV-1 infection in human: molecular network, modeling and docking studies

The major causative agent for Acquired Immune Deficiency Syndrome (AIDS) is Human Immunodeficiency Virus-1 (HIV-1). HIV-1 is a predominant subtype of HIV which counts on human cellular mechanism virtually in every aspect of its life cycle. Binding of viral envelope glycoprotein-gp120 with human cell surface CD4 receptor triggers the early infection stage of HIV-1. This study focuses on the interaction interface between these two proteins that play a crucial role for viral infectivity. The CD4-gp120 interaction interface has been studied through a comprehensive protein-protein interaction network (PPIN) analysis and highlighted as a useful step towards identifying potential therapeutic drug targets against HIV-1 infection. We prioritized gp41, Nef and Tat proteins of HIV-1 as valuable drug targets at early stage of viral infection. Lack of crystal structure has made it difficult to understand the biological implication of these proteins during disease progression. Here, computational protein modeling techniques and molecular dynamics simulations were performed to generate three-dimensional models of these targets. Besides, molecular docking was initiated to determine the desirability of these target proteins for already available HIV-1 specific drugs which indicates the usefulness of these protein structures to identify an effective drug combination therapy against AIDS.

A Quantitative Approach to Evaluate the Impact of Fluorescent Labeling on Membrane-Bound HIV-Gag Assembly by Titration of Unlabeled Proteins

The assembly process of the human immunodeficiency virus 1 (HIV-1) is driven by the viral polyprotein Gag. Fluorescence imaging of Gag protein fusions is widely performed and has revealed important information on viral assembly. Gag fusion proteins are commonly co-transfected with an unlabeled form of Gag to prevent labeling artifacts such as morphological defects and decreased infectivity. Although viral assembly is widely studied on individual cells, the efficiency of the co-transfection rescue has never been tested at the single cell level. Here, we first develop a methodology to quantify levels of unlabeled to labeled Gag in single cells using a fluorescent reporter protein for unlabeled Gag and fluorescence correlation spectroscopy. Using super-resolution imaging based on photoactivated localization microscopy (PALM) combined with molecular counting we then study the nanoscale morphology of Gag clusters as a function of unlabeled to labeled Gag ratios in single cells. We show that for a given co-transfection ratio, individual cells express a wide range of protein ratios, necessitating a quantitative read-out for the expression of unlabeled Gag. Further, we show that monomerically labeled Gag assembles into membrane-bound clusters that are morphologically indistinguishable from mixtures of unlabeled and labeled Gag.

Driving DNA transposition by lentiviral protein transduction

Gene vectors derived from DNA transposable elements have become powerful molecular tools in biomedical research and are slowly moving into the clinic as carriers of therapeutic genes. Conventional uses of DNA transposon-based gene vehicles rely on the intracellular production of the transposase protein from transfected nucleic acids. The transposase mediates mobilization of the DNA transposon, which is typically provided in the context of plasmid DNA. In recent work, we established lentiviral protein transduction from Gag precursors as a new strategy for direct delivery of the transposase protein. Inspired by the natural properties of infecting viruses to carry their own enzymes, we loaded lentivirus-derived particles not only with vector genomes carrying the DNA transposon vector but also with hundreds of transposase subunits. Such particles were found to drive efficient transposition of the piggyBac transposable element in a range of different cell types, including primary cells, and offer a new transposase delivery approach that guarantees short-term activity and limits potential cytotoxicity. DNA transposon vectors, originally developed and launched as a non-viral alternative to viral integrating vectors, have truly become viral. Here, we briefly review our findings and speculate on the perspectives and potential advantages of transposase delivery by lentiviral protein transduction.

A facile quantitative assay for viral particle genesis reveals cooperativity in virion assembly and saturation of an antiviral protein

Conventional assays of viral particle assembly and release are time consuming and laborious. We have developed an enzymatic virus-like particle (VLP) genesis assay that rapid and quantitative and is also versatile and applicable to diverse viruses including HIV-1 and Ebola virus. Using this assay, which has a dynamic range of several orders of magnitude, we show that the efficiency of VLP assembly and release, i.e., the fraction of the expressed protein that is assembled into extracellular particles, is dependent on the absolute level of expression of either HIV-1 Gag or Ebola virus VP40. We also demonstrate that the activity of the antiviral factor tetherin is dependent on the level of HIV-1 Gag expression and the numbers of VLPs generated, and appears to become saturated as these parameters are increased.

Antiviral activity of recombinant ankyrin targeted to the capsid domain of HIV-1 Gag polyprotein

Background

Ankyrins are cellular mediators of a number of essential protein-protein interactions. Unlike intrabodies, ankyrins are composed of highly structured repeat modules characterized by disulfide bridge-independent folding. Artificial ankyrin molecules, designed to target viral components, might act as intracellular antiviral agents and contribute to the cellular immunity against viral pathogens such as HIV-1.

Results

A phage-displayed library of artificial ankyrins was constructed, and screened on a polyprotein made of the fused matrix and capsid domains (MA-CA) of the HIV-1 Gag precursor. An ankyrin with three modules named Ank^GAG1D4 (16.5 kDa) was isolated. Ank^GAG1D4 and MA-CA formed a protein complex with a stoichiometry of 1:1 and a dissociation constant of K_d ~ 1 μM, and the Ank^GAG1D4 binding site was mapped to the N-terminal domain of the CA, within residues 1-110. HIV-1 production in SupT1 cells stably expressing Ank^GAG1D4 in both N-myristoylated and non-N-myristoylated versions was significantly reduced compared to control cells. Ank^GAG1D4 expression also reduced the production of MLV, a phylogenetically distant retrovirus. The Ank^GAG1D4-mediated antiviral effect on HIV-1 was found to occur at post-integration steps, but did not involve the Gag precursor processing or cellular trafficking. Our data suggested that the lower HIV-1 progeny yields resulted from the negative interference of Ank^GAG1D4-CA with the Gag assembly and budding pathway.

Conclusions

The resistance of Ank^GAG1D4-expressing cells to HIV-1 suggested that the CA-targeted ankyrin Ank^GAG1D4 could serve as a protein platform for the design of a novel class of intracellular inhibitors of HIV-1 assembly based on ankyrin-repeat modules.