Explore the vast range of titles available.

The structure of the oligomeric hepatitis C virus viroporin p7 protein, solved by NMR spectroscopy, is reported; this protein can self-assemble into a channel complex that conducts cations and has a funnel-like channel architecture. Structure of a hepatitis virus cation channel Hepatitis C virus (HCV) is a major cause of liver diseases and cancer. With no protective vaccine available and therapeutic options still limited, it is important to explore new therapeutic targets. Here James Chou and colleagues report the structure of the oligomeric hepatitis C virus viroporin p7 protein, solved by NMR spectroscopy. This protein can self-assemble into a channel complex that conducts cations. A high-resolution view of the channel hexamer reveals novel funnel-like channel architecture and functional investigations identify residues important for channel activity. The hepatitis C virus (HCV) has developed a small membrane protein, p7, which remarkably can self-assemble into a large channel complex that selectively conducts cations 1 , 2 , 3 , 4 . We wanted to examine the structural solution that the viroporin adopts in order to achieve selective cation conduction, because p7 has no homology with any of the known prokaryotic or eukaryotic channel proteins. The activity of p7 can be inhibited by amantadine and rimantadine 2 , 5 , which are potent blockers of the influenza M2 channel 6 and licensed drugs against influenza infections 7 . The adamantane derivatives have been used in HCV clinical trials 8 , but large variation in drug efficacy among the various HCV genotypes has been difficult to explain without detailed molecular structures. Here we determine the structures of this HCV viroporin as well as its drug-binding site using the latest nuclear magnetic resonance (NMR) technologies. The structure exhibits an unusual mode of hexameric assembly, where the individual p7 monomers, i, not only interact with their immediate neighbours, but also reach farther to associate with the i +2 and i +3 monomers, forming a sophisticated, funnel-like architecture. The structure also points to a mechanism of cation selection: an asparagine/histidine ring that constricts the narrow end of the funnel serves as a broad cation selectivity filter, whereas an arginine/lysine ring that defines the wide end of the funnel may selectively allow cation diffusion into the channel. Our functional investigation using whole-cell channel recording shows that these residues are critical for channel activity. NMR measurements of the channel–drug complex revealed six equivalent hydrophobic pockets between the peripheral and pore-forming helices to which amantadine or rimantadine binds, and compound binding specifically to this position may allosterically inhibit cation conduction by preventing the channel from opening. Our data provide a molecular explanation for p7-mediated cation conductance and its inhibition by adamantane derivatives.

Influenza changes channels Until recently, the pH-gated proton channel of influenza A virus, M2, was effectively targeted by amantadine-based antivirals, but resistance to these drugs is now widespread. Two groups now present structural studies of M2 proton channel. Jason Schnell and James Chou determine the structure of a 38-residue segment of M2, in complex with rimantadine, by NMR spectroscopy. Amanda Stouffer et al . determined the crystal structure of a 25-residue fragment of M2, with and without amantadine, using X-ray diffraction. Strikingly, the resulting structures suggest two very different mechanisms by which the drug inhibits the channel. The proposed mechanisms are discussed by Christopher Miller in an accompanying News & Views article. A vital component of influenza A virus' replication machinery is the M2 proton channel. Until recently, M2 was effectively targeted by amantadane-based antivirals, but resistance to these drugs is now so widespread that they have become ineffective. In the first of two related papers, the structure of a 38-residue segment of M2, in complex with rimantadine, is determined by NMR spectroscopy. It is concluded that a rimantadine molecule binds to each monomer at the protein–lipid interface and inhibits the tetrameric channel allosterically. The integral membrane protein M2 of influenza virus forms pH-gated proton channels in the viral lipid envelope 1 . The low pH of an endosome activates the M2 channel before haemagglutinin-mediated fusion. Conductance of protons acidifies the viral interior and thereby facilitates dissociation of the matrix protein from the viral nucleoproteins—a required process for unpacking of the viral genome 2 . In addition to its role in release of viral nucleoproteins, M2 in the trans-Golgi network (TGN) membrane prevents premature conformational rearrangement of newly synthesized haemagglutinin during transport to the cell surface by equilibrating the pH of the TGN with that of the host cell cytoplasm 3 . Inhibiting the proton conductance of M2 using the anti-viral drug amantadine or rimantadine inhibits viral replication 4 , 5 , 6 , 7 . Here we present the structure of the tetrameric M2 channel in complex with rimantadine, determined by NMR. In the closed state, four tightly packed transmembrane helices define a narrow channel, in which a ‘tryptophan gate’ is locked by intermolecular interactions with aspartic acid. A carboxy-terminal, amphipathic helix oriented nearly perpendicular to the transmembrane helix forms an inward-facing base. Lowering the pH destabilizes the transmembrane helical packing and unlocks the gate, admitting water to conduct protons, whereas the C-terminal base remains intact, preventing dissociation of the tetramer. Rimantadine binds at four equivalent sites near the gate on the lipid-facing side of the channel and stabilizes the closed conformation of the pore. Drug-resistance mutations are predicted to counter the effect of drug binding by either increasing the hydrophilicity of the pore or weakening helix–helix packing, thus facilitating channel opening.

Rimantadine is an adamantane derivative, known for its antiviral activity against infections caused by influenza A viruses. The purpose of the present study was to synthesize 6 new rimantadine derivatives, containing short-chain (Gly, Ala, β-Ala) and bulky (Leu, Ile, Val) amino acids and to investigate their antimicrobial activity against the strains NBIMCC 3562 and NBIMCC 8785. All derivatives were successfully obtained in good yields by using the TBTU/TEA condensation system. Their antimicrobial properties were established by determining the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) against both test strains. The MIC was obtained via a microdilution method, whereas the MBC – via a spread plate method. Most derivatives showed antimicrobial activity, with stronger effects against the Gram-positive strain NBIMCC 3562. Among them, -Ile-Rim was the most effective derivative against both bacterial strains.

A zone-fluidics (ZF) based automated fluorimetric sensor for the determination of pharmaceutically active adamantine derivatives, i.e., amantadine (AMA), memantine (MEM) and rimantadine (RIM) is reported. Discrete zones of the analytes and reagents (o-phthalaldehyde and N-acetylcysteine) mix and react under stopped-flow conditions to yield fluorescent iso-indole derivatives (λex/ λem = 340/455 nm). The proposed ZF sensor was developed and validated to prove suitable for quality control tests (assay and content uniformity) of commercially available formulations purchased from the Greek market (EU licensed) and from non-EU web-pharmacies at a sampling rate of 16 h−1. Interestingly, a formulation obtained through the internet and produced in a third—non-EU—country (AMA capsules, 100 mg per cap), was found to be out of specifications (mean assay of 85.3%); a validated HPLC method was also applied for confirmatory purposes.

Flaviviruses , including Zika virus (ZIKV), are a significant global health concern, yet no licensed antivirals exist to treat disease. The small membrane (M) protein plays well-defined roles during viral egress and remains within virion membranes following release and maturation. However, it is unclear whether M plays a functional role in this setting. Here, we show that M forms oligomeric membrane-permeabilising channels in vitro, with increased activity at acidic pH and sensitivity to the prototypic channel-blocker, rimantadine. Accordingly, rimantadine blocked an early stage of ZIKV cell culture infection. Structure-based channel models, comprising hexameric arrangements of two trans -membrane domain protomers were shown to comprise more stable assemblages than other oligomers using molecular dynamics simulations. Models contained a predicted lumenal rimantadine-binding site, as well as a second druggable target region on the membrane-exposed periphery. In silico screening enriched for repurposed drugs/compounds predicted to bind to either one site or the other. Hits displayed superior potency in vitro and in cell culture compared with rimantadine, with efficacy demonstrably linked to virion-resident channels. Finally, rimantadine effectively blocked ZIKV viraemia in preclinical models, supporting that M constitutes a physiologically relevant target. This could be explored by repurposing rimantadine, or development of new M-targeted therapies.

We investigate the binding of native β-cyclodextrin (β-CD) and eight novel β-CD derivatives with two different guest compounds, using isothermal calorimetry and 2D NOESY NMR. In all cases, the stoichiometry is 1:1 and binding is exothermic. Overall, modifications at the 3′ position of β-CD, which is at the secondary face, weaken binding by several kJ/mol relative to native β-CD, while modifications at the 6′ position (primary face) maintain or somewhat reduce the binding affinity. The variations in binding enthalpy are larger than the variations in binding free energy, so entropy–enthalpy compensation is observed. Characterization of the bound conformations with NOESY NMR shows that the polar groups of the guests may be situated at either face, depending on the host molecule, and, in some cases, both orientations are populated. The present results were used in the SAMPL7 blinded prediction challenge whose results are detailed in the same special issue of JCAMD.

A series of nineteen amino acid analogues of amantadine (Amt) and rimantadine (Rim) were synthesized and their antiviral activity was evaluated against influenza virus A (H3N2). Among these analogues, the conjugation of rimantadine with glycine illustrated high antiviral activity combined with low cytotoxicity. Moreover, this compound presented a profoundly high stability after in vitro incubation in human plasma for 24 h. Its thermal stability was established using differential and gravimetric thermal analysis. The crystal structure of glycyl-rimantadine revealed that it crystallizes in the orthorhombic Pbca space group. The structure–activity relationship for this class of compounds was established, with CoMFA (Comparative Molecular Field Analysis) 3D-Quantitative Structure Activity Relationships (3D-QSAR) studies predicting the activities of synthetic molecules. In addition, molecular docking studies were conducted, revealing the structural requirements for the activity of the synthetic molecules.

Influenza is a disease of significant morbidity and mortality. The number of anti-influenza drugs is small; many of them stimulate the appearance of resistant strains. This article presents the results of assessing the antiviral activity of 1,2,3-triazole-containing derivatives of alkaloid lupinine for their ability to suppress the reproduction of orthomyxoviruses (influenza viruses: A/Vladivostok/2/09 (H1N1) and A/Almaty/8/98 (H3N2)). The ability of (1S,9aR)-1-[(1,2,3-triazol-1-yl)-methyl]octahydro-1H-quinolizines with aryl-, 4-((4-formylphenoxy)methyl)- or 4-((3-tert-butyl-5-ethyl-2-hydroxy-benzoyloxy)methyl)- substituents at the C-4 position of the triazole ring to reduce the infectivity of the virus when processing virus-containing material was established, indicating good prospects for the studied compounds as virucidal agents affecting extracellular virions. The experimental results demonstrated that the triazolyl lupinine derivatives exhibited varying degrees of affinity for both hemagglutinin and neuraminidase proteins. Furthermore, these compounds demonstrated inhibitory effects on the replication of influenza viruses with different antigenic subtypes. The obtained biological data are in agreement with the results of molecular docking, which showed strong binding energies of the investigated compounds under study with biological targets—hemagglutinin and neuraminidase proteins. Following the evaluation of antiviral efficacy among the studied triazolyl derivatives of lupinine, four compounds have been identified for subsequent comprehensive in vitro and in vivo investigations to further elucidate their antiviral properties.

M2 proton channel of H1N1 influenza A virus is the target protein of anti-flu drugs amantadine and rimantadine. However, the two once powerful adamantane-based drugs lost their 90% bioactivity because of mutations of virus in recent twenty years. The NMR structure of the M2 channel protein determined by Schnell and Chou (Nature, 2008, 451, 591-595) may help people to solve the drug-resistant problem and develop more powerful new drugs against H1N1 influenza virus. Docking calculation is performed to build the complex structure between receptor M2 proton channel and ligands, including existing drugs amantadine and rimantadine, and two newly designed inhibitors. The computer-aided drug design methods are used to calculate the binding free energies, with the computational biology techniques to analyze the interactions between M2 proton channel and adamantine-based inhibitors. 1) The NMR structure of M2 proton channel provides a reliable structural basis for rational drug design against influenza virus. 2) The channel gating mechanism and the inhibiting mechanism of M2 proton channel, revealed by the NMR structure of M2 proton channel, provides the new ideas for channel inhibitor design. 3) The newly designed adamantane-based inhibitors based on the modeled structure of H1N1-M2 proton channel have two pharmacophore groups, which act like a \"barrel hoop\", holding two adjacent helices of the H1N1-M2 tetramer through the two pharmacophore groups outside the channel. 4) The inhibitors with such binding mechanism may overcome the drug resistance problem of influenza A virus to the adamantane-based drugs.

Resistance to amantadine has been detected at an extraordinarily high frequency in isolates of influenza A virus. Dr. Frederick Hayden discusses the implications of resistance to antiviral agents for the current clinical management of influenza and for planning for a possible pandemic. The Centers for Disease Control and Prevention (CDC) recently issued an alert instructing clinicians to avoid using M2 ion-channel inhibitors (amantadine and rimantadine) during the current influenza season because amantadine resistance has been detected at an extraordinarily high frequency in isolates of influenza A (H3N2) virus (see table). 1 – 3 This and other reports 4 raise important questions regarding the implications of resistance to antiviral agents for the current clinical management of influenza and for planning for a possible pandemic. Phenotypic amantadine resistance was first described soon after the drug was discovered in the early 1960s, and subsequent work has established that . . .