The conserved residue Arg46 in the N-terminal heptad repeat domain of HIV-1 gp41 is critical for viral fusion and entry

Heptad stereotypy, S/Q layering, and remote origin of the SARS-CoV-2 fusion core

The fusion of the SARS-CoV-2 virus with cells, a key event in the pathogenesis of Covid-19, depends on the assembly of a six-helix fusion core (FC) formed by portions of the spike protein heptad repeats (HRs) 1 and 2. Despite the critical role in regulating infectivity, its distinctive features, origin, and evolution are scarcely understood. Thus, we undertook a structure-guided positional and compositional analysis of the SARS-CoV-2 FC, in comparison with FCs of related viruses, tracing its origin and ongoing evolution. We found that clustered amino acid substitutions within HR1, distinguishing SARS-CoV-2 from SARS-CoV-1, enhance local heptad stereotypy and increase sharply the FC serine-to-glutamine (S/Q) ratio, determining a neat alternate layering of S-rich and Q-rich subdomains along the post-fusion structure. Strikingly, SARS-CoV-2 ranks among viruses with the highest FC S/Q ratio, together with highly syncytiogenic respiratory pathogens (RSV, NDV), whereas MERS-Cov, HIV, and Ebola viruses display low ratios, and this feature reflects onto S/Q segregation and H-bonding patterns. Our evolutionary analyses revealed that the SARS-CoV-2 FC occurs in other SARS-CoV-1-like Sarbecoviruses identified since 2005 in Hong Kong and adjacent regions, tracing its origin to >50 years ago with a recombination-driven spread. Finally, current mutational trends show that the FC is varying especially in the FC1 evolutionary hotspot. These findings establish a novel analytical framework illuminating the sequence/structure evolution of the SARS-CoV-2 FC, tracing its long history within Sarbecoviruses, and may help rationalize the evolution of the fusion machinery in emerging pathogens and the design of novel therapeutic fusion inhibitors.

Measures for diagnosing and treating infections by a novel coronavirus responsible for a pneumonia outbreak originating in Wuhan, China

On 10 January 2020, a new coronavirus causing a pneumonia outbreak in Wuhan City in central China was denoted as 2019-nCoV by the World Health Organization (WHO). As of 24 January 2020, there were 887 confirmed cases of 2019-nCoV infection, including 26 deaths, reported in China and other countries. Therefore, combating this new virus and stopping the epidemic is a matter of urgency. Here, we focus on advances in research and development of fast diagnosis methods, as well as potential prophylactics and therapeutics to prevent or treat 2019-nCoV infection.

Structural and functional characterization of HIV-1 cell fusion inhibitor T20

OBJECTIVE

The peptide drug T20 (enfuvirtide), derived from the C-terminal heptad repeat region of HIV-1 gp41, is the only membrane fusion inhibitor available for treatment of viral infection; however, its mechanism of action remains elusive and its structural basis is lacking.

DESIGN

We focused on determining the crystal structure of T20 in complex with N39, a target mimic peptide derived from the N-terminal heptad repeat region of gp41. On the basis of the structural information, the mechanisms of action of T20 and its resistance were further characterized.

METHODS

A panel of peptides was synthesized. The T20/N39 complex was assembled for crystallization studies. Circular dichroism spectroscopy, isothermal titration calorimetry (ITC), native polyacrylamide gel electrophoresis (N-PAGE), and mutational analysis were applied to analyze the structural and functional properties.

RESULTS

A crystal structure of six-helical bundle (6-HB) structure formed by T20 and N39 was determined with a resolution limit of 2.3 Å, which revealed the critical intrahelical and interhelical interactions underlying the mechanism of action of T20 and its resistance mutations. Although the structural properties in the C-terminal tryptophan-rich motif (TRM) of T20 and the fusion peptide proximal region (FPPR) of N39 could not be finely defined by the structure, the data from biophysical and mutational analyses verified the essential roles of the TRM and FPPR motifs for the binding and inhibitory activities of T20.

CONCLUSION

For the first time, our studies provide a structural basis of T20, which help our understanding on the mechanisms of HIV-1 fusion and its inhibition.

Molecular dynamics modeling the synthetic and biological polymers interactions pre-studied via docking: anchors modified polyanions interference with the HIV-1 fusion mediator

In previous works we reported the design, synthesis and in vitro evaluations of synthetic anionic polymers modified by alicyclic pendant groups (hydrophobic anchors), as a novel class of inhibitors of the human immunodeficiency virus type 1 (HIV-1) entry into human cells. Recently, these synthetic polymers interactions with key mediator of HIV-1 entry-fusion, the tri-helix core of the first heptad repeat regions [HR1]3 of viral envelope protein gp41, were pre-studied via docking in terms of newly formulated algorithm for stepwise approximation from fragments of polymeric backbone and side-group models toward real polymeric chains. In the present article the docking results were verified under molecular dynamics (MD) modeling. In contrast with limited capabilities of the docking, the MD allowed of using much more large models of the polymeric ligands, considering flexibility of both ligand and target simultaneously. Among the synthesized polymers the dinorbornen anchors containing alternating copolymers of maleic acid were selected as the most representative ligands (possessing the top anti-HIV activity in vitro in correlation with the highest binding energy in the docking). To verify the probability of binding of the polymers with the [HR1]3 in the sites defined via docking, various starting positions of polymer chains were tried. The MD simulations confirmed the main docking-predicted priority for binding sites, and possibilities for axial and belting modes of the ligands-target interactions. Some newly MD-discovered aspects of the ligand's backbone and anchor units dynamic cooperation in binding the viral target clarify mechanisms of the synthetic polymers anti-HIV activity and drug resistance prevention.