Yeast two-hybrid assay for examining human immunodeficiency virus protease heterodimer formation with dominant-negative inhibitors and multidrug-resistant variants

Help or Hinder: Protein Host Factors That Impact HIV-1 Replication

Interactions between human immunodeficiency virus type 1 (HIV-1) and the host factors or restriction factors of its target cells determine the cell's susceptibility to, and outcome of, infection. Factors intrinsic to the cell are involved at every step of the HIV-1 replication cycle, contributing to productive infection and replication, or severely attenuating the chances of success. Furthermore, factors unique to certain cell types contribute to the differences in infection between these cell types. Understanding the involvement of these factors in HIV-1 infection is a key requirement for the development of anti-HIV-1 therapies. As the list of factors grows, and the dynamic interactions between these factors and the virus are elucidated, comprehensive and up-to-date summaries that recount the knowledge gathered after decades of research are beneficial to the field, displaying what is known so that researchers can build off the groundwork of others to investigate what is unknown. Herein, we aim to provide a review focusing on protein host factors, both well-known and relatively new, that impact HIV-1 replication in a positive or negative manner at each stage of the replication cycle, highlighting factors unique to the various HIV-1 target cell types where appropriate.

Novel macromolecular inhibitors of human immunodeficiency virus-1 protease

An intracellularly expressed defective human immunodeficiency virus type-1 (HIV-1) protease (PR) monomer could function as a dominant-negative inhibitor of the enzyme that requires dimerization for activity. Based on in silico studies, two mutant PRs harboring hydrophilic mutations, capable of forming favorable inter- and intra-subunit interactions, were selected: PR(RE) containing Asp25Arg and Gly49Glu mutations, and PR(RER) containing an additional Ile50Arg mutation. The mutants were expressed and tested by PR assays, nuclear magnetic resonance (NMR) and cell culture experiments. The mutant PRs showed dose-dependent inhibition of the wild-type PR in a fluorescent microtiter plate PR assay. Furthermore, both mutants were retained by hexahistidine-tagged wild-type HIV-1 PR immobilized on nickel-chelate affinity resin. For the first time, heterodimerization between wild-type and dominant-negative mutant PRs were also demonstrated by NMR spectroscopy. (1)H-(15)N Heteronuclear Single Quantum Coherence NMR spectra showed that although PR(RE) has a high tendency to aggregate, PR(RER) exists mainly as a folded monomer at 25-35 microM concentration, but in the presence of wild-type PR in a ratio of 1:1, heterodimerization occurs with both mutants. While the recombinant virus containing the PR(RE) sequence showed only very low level of expression, expression of the viral proteins of the virus with the PR(RER) sequence was comparable with that of the wild-type. In cell culture experiments, infectivity of viral particles containing PR(RER) protein was reduced by 82%, at mutant to wild-type infective DNA ratio of 2:1.

Two-hybrid systems and their usage in infection biology

Two-hybrid systems are powerful tools to study protein-protein interactions in biological systems. The role of protein-protein interactions involved in pathogenesis of bacterial and viral infections were defined by using yeast or bacterial two-hybrid screens. Examples are given to highlight the specificity of interactions in signaling pathways, in regulation, secretion and structure-function relationships of virulence factors and their cellular targets. Two-hybrid systems were also used to establish large-scale protein interaction maps of viral and bacterial pathogens, that might be useful to identify targets for new drugs or vaccines.

HIV protease as a target for retrovirus vector-mediated gene therapy

The dimeric aspartyl protease of HIV has been the subject of intense research for almost a decade. Knowledge of the substrate specificity and catalytic mechanism of this enzyme initially guided the development of several potent peptidomimetic small molecule inhibitors. More recently, the solution of the HIV protease structure led to the structure-based design of improved peptidomimetic and non-peptidomimetic antiviral compounds. Despite the qualified success of these inhibitors, the high mutation rate associated with RNA viruses continues to hamper the long-term clinical efficacy of HIV protease inhibitors. The dimeric nature of the viral protease has been conducive to the investigation of dominant-negative inhibitors of the enzyme. Some of these inhibitors are defective protease monomers that interact with functional monomers to form inactive protease heterodimers. An advantage of macromolecular inhibitors as compared to small-molecule inhibitors is the increased surface area of interaction between the inhibitor and the target gene product. Point mutations that preserve enzyme activity but confer resistance to small-molecule inhibitors are less likely to have an adverse effect on macromolecular interactions. The use of efficient retrovirus vectors has facilitated the delivery of these macromolecular inhibitors to primary human lymphocytes. The vector-transduced cells were less susceptible to HIV infection in vitro, and showed similar levels of protection compared to other macromolecular inhibitors of HIV replication, such as RevM10. These preliminary results encourage the further development of dominant-negative HIV protease inhibitors as a gene therapy-based antiviral strategy.