HIV-1 gp41 transmembrane oligomerization monitored by FRET and FCS

Quo vadis FRET? Förster's method in the era of superresolution

Although the theoretical foundations of Förster resonance energy transfer (FRET) were laid in the 1940s as part of the quantum physical revolution of the 20th century, it was only in the 1970s that it made its way to biology as a result of the availability of suitable measuring and labeling technologies. Thanks to its ease of application, FRET became widely used for studying molecular associations on the nanometer scale. The development of superresolution techniques at the turn of the millennium promised an unprecedented insight into the structure and function of molecular complexes. Without downplaying the significance of superresolution microscopies this review expresses our view that FRET is still a legitimate tool in the armamentarium of biologists for studying molecular associations since it offers distinct advantages and overcomes certain limitations of superresolution approaches.

Discoveries and developments of CXCR4-targeted HIV-1 entry inhibitors

The chemokine receptor CXCR4 is required for the entry of human immunodeficiency virus type 1 (HIV-1) into target cells and its expression correlates with more profound pathogenicity, rapid progression to acquired immunodeficiency syndrome (AIDS), and greater AIDS-related mortality. There is still no cure for AIDS and no method for preventing or eradicating HIV-1 infection. HIV-1 entry begins with the interaction of the viral envelope glycoprotein gp120 and the primary receptor CD4, and subsequently with the coreceptors, CCR5 or CXCR4, on the host cells. Blocking the interaction of HIV-1 and its coreceptors is therefore a promising strategy for developing new HIV-1 entry inhibitors. This approach has a dual benefit, as it prevents HIV-1 infection and progression while also targeting the reservoirs of HIV-1 infected, coreceptor positive macrophages and memory T cells. To date, multiple classes of CXCR4-targeted anti-HIV-1 inhibitors have been discovered and are now at different preclinical and clinical stages. In this review, we highlight the studies of CXCR4-targeted small-molecule and peptide HIV-1 entry inhibitors discovered during the last two decades and provide a reference for further potential HIV-1 exploration in the future.

Impact statement

This minireview summarized the current progress in the identification of CXCR4-targeted HIV-1-entry inhibitors based on discovery/developmental approaches. It also provided a discussion of the inhibitor structural features, antiviral activities, and pharmacological properties. Unlike other reviews on anti-HIV-1 drug development, which have generally emphasized inhibitors that target intracellular viral replication and host genomic integration, this review focused on the drug discovery approaches taken to develop viral-entry inhibitors aimed at disturbing the initial step of viral interaction with uninfected host cells and preventing the subsequent viral replication/genomic integration. This review amalgamated recently published and important work on bivalent CXCR4-targeted anti-HIV-1-entry candidates/conjugates, discussed the research challenges faced in developing drugs to prevent and eradicate HIV-1 infection, and provided a perspective on strategies that can lead to future drug discoveries. The findings and strategies summarized in this review will be of interest to investigators throughout the microbiological, pharmaceutical, and translational research communities.

Hydrophobic matching of HIV-1 Vpu transmembrane helix-helix interactions is optimized for subcellular location

The HIV-1 accessory protein Vpu mediates the downregulation of several host cell proteins, an activity that is critical for viral replication in vivo. As the first step in directing cell-surface proteins to internal cellular compartments, and in many cases degradation, Vpu binds a subset of its target proteins through their transmembrane domains. Each of the known targets of Vpu are synthesized in the ER, and must traverse the different membrane environments found along the secretory pathway, thus it is important to consider how membrane composition might influence the interactions between Vpu and its targets. We have used Förster resonance energy transfer (FRET) to measure the oligomerization of Vpu with the transmembrane domains of target proteins in model membranes of varying lipid composition. Our data show that both lipid bilayer thickness and acyl chain order can significantly influence monomer-oligomer equilibria within the Vpu-target system. Changes in oligomerization levels were found to be non-specific with no single Vpu-target interaction being favored under any condition. Our analysis of the influence of the membrane environment on the strength of helix-helix interactions between Vpu and its targets in vitro suggests that the strength of Vpu-target interactions in vivo will be partially dependent on the membrane environment found in specific membrane compartments.

Virtual Screening, Biological Evaluation, and 3D-QSAR Studies of New HIV-1 Entry Inhibitors That Function via the CD4 Primary Receptor

Human immunodeficiency virus type 1 (HIV-1) is responsible for the majority of HIV infections worldwide, and we still lack a cure for this infection. Blocking the interaction of HIV-1 and its primary receptor CD4 is one strategy for identifying new anti-HIV-1 entry inhibitors. Here we report the discovery of a novel ligand that can inhibit HIV-1 entry and infection via CD4. Biological and computational analyses of this inhibitor and its analogs, using bioactivity evaluation, Rule of Five (RO5), comparative molecular field analysis (CoMFA)/comparative molecular similarity index analysis (CoMSIA) models, and three-dimensional quantitative structure-activity relationship (3D-QSAR), singled out compound 3 as a promising lead molecule for the further development of therapeutics targeting HIV-1 entry. Our study demonstrates an effective approach for employing structure-based, rational drug design techniques to identify novel antiviral compounds with interesting biological activities.