Susceptibility of antiviral drugs against 2009 influenza A (H1N1) virus

The recent outbreak of the novel strain of influenza A (H1N1) virus has raised a global concern of the future risk of a pandemic. To understand at the molecular level how this new H1N1 virus can be inhibited by the current anti-influenza drugs and which of these drugs it is likely to already be resistant to, homology modeling and MD simulations have been applied on the H1N1 neuraminidase complexed with oseltamivir, and the M2-channel with adamantanes bound. The H1N1 virus was predicted to be susceptible to oseltamivir, with all important interactions with the binding residues being well conserved. In contrast, adamantanes are not predicted to be able to inhibit the M2 function and have completely lost their binding with the M2 residues. This is mainly due to the fact that the M2 transmembrane of the new H1N1 strain contains the S31N mutation which is known to confer resistance to adamantanes.     

Dynamics of the protein structure of T169S pyranose 2‐oxidase in solution: Molecular dynamics simulation

Pyranose 2‐oxidase (P2O) from Trametes multicolor contains FAD as cofactor, and forms a tetramer. The protein structure of a mutated P2O, T169S (Thr169 is replaced by Ser), in solution was studied by means of molecular dynamics simulation and analyses of photoinduced electron transfer (ET) from Trp168 to excited isoalloxazine (Iso*), and was compared with wild type (WT) P2O. Hydrogen bonding between Iso and nearby amino acids was very similar as between T169S and WT protein. Distances between Iso and Tyr456 were extremely heterogeneous among the subunits, 1.7 (1.5 in WT) in subunit A (Sub A), 0.97 (2.2 in WT) in Sub B, 1.3 (2.1 in WT) in Sub C, 1.3 nm (2.0 in WT) in Sub D. Mean values of root of mean square fluctuation over all residues were greater by four times than those in WT. This suggests that the protein structure of T169S is much more flexible than that of WT. Electrostatic (ES) energies between Iso anion in one subunit and ionic groups in the entire protein were evaluated. It was found that more than 50% of the total ES energy in each subunit is contributed from other subunits. Reported fluorescence decays were analyzed by a method as WT, previously reported. Electron affinities of Iso* in T169S were appreciably higher than those in WT. Static dielectric constants near Iso and Trp168 were also quite higher in T169S than those in WT.     

Source of oseltamivir resistance in avian influenza H5N1 virus with the H274Y mutation

Molecular dynamics simulations were carried out for the mutant oseltamivir-NA complex, to provide detailed information on the oseltamivir-resistance resulting from the H274Y mutation in neuraminidase (NA) of avian influenza H5N1 viruses. In contrast with a previous proposal, the H274Y mutation does not prevent E276 and R224 from forming the hydrophobic pocket for the oseltamivir bulky group. Instead, reduction of the hydrophobicity and size of pocket in the area around an ethyl moiety at this bulky group were found to be the source of the oseltamivir-resistance. These changes were primarily due to the dramatic rotation of the hydrophilic –COO⁻ group of E276 toward the ethyl moiety. In addition, hydrogen-bonding interactions with N1 residues at the -NH₃ ⁺ and -NHAc groups of oseltamivir were replaced by a water molecule. The calculated binding affinity of oseltamivir to NA was significantly reduced from −14.6 kcal mol⁻¹ in the wild-type to −9.9 kcal mol⁻¹ in the mutant-type.     

How does each substituent functional group of oseltamivir lose its activity against virulent H5N1 influenza mutants?

To reveal the source of oseltamivir-resistance in influenza (A/H5N1) mutants, the drug-target interactions at each functional group were investigated using MD/LIE simulations. Oseltamivir in the H274Y mutation primarily loses the electrostatic and the vdW interaction energies at the –NH₃⁺ and –OCHEt₂ moieties corresponding to the weakened hydrogen-bonds and changed distances to N1 residues. Differentially, the N294S mutation showed small changes of binding energies and intermolecular interactions. Interestingly, the presence of different conformations of E276 positioned between the –OCHEt₂ group and the mutated residue is likely to play an important role in oseltamivir-resistant identification. In the H274Y mutant, it moves towards the –OCHEt₂ group leading to a reduction in hydrophobicity and pocket size, whilst in the N294S mutant it acts as the hydrogen network center bridging with R224 and the mutated residue S294. The molecular details have answered a question of how the H274Y and N294S mutations confer the high- and medium-level of oseltamivir-resistance to H5N1.     

Density functional investigation of hydrogen gas adsorption on Fe?doped pristine and Stone?Wales defected single?walled carbon nanotubes

The adsorptions of hydrogen molecule of the Fe?-?doped pristine and Stone?-?Wales defected armchair (5,5) single?-?walled carbon nanotubes (SWCNTs) compared with the pristine SWCNT were investigated by using the density functional theory at the B3LYP/LanL2DZ level. The doping of Fe atom into SWCNTs occurring via an exothermic process was found. The adsorptions of hydrogen molecule on the Fe?-?doped structures of either perfect or SW defected SWCNTs are stronger than on their corresponding undoped structures. The structural and electronic properties of the pristine and SW defected SWCNTs, their Fe?-?doped structures and their hydrogen molecule adsorptions are reported.     

Hybrid quantum mechanical/molecular mechanical molecular dynamics simulations of HIV-1 integrase/inhibitor complexes

Human immunodeficiency virus (HIV)-1 integrase (IN) is an attractive target for development of acquired immunodeficiency syndrome chemotherapy. In this study, conventional and coupled quantum mechanical and molecular mechanical (QM/MM) molecular dynamics (MD) simulations of HIV-1 IN complexed with 5CITEP (IN-5CITEP) were carried out. In addition to differences in the bound position of 5CITEP, significant differences at the two levels of theory were observed in the metal coordination geometry and the areas involving residues 116-119 and 140-166. In the conventional MD simulation, the coordination of Mg(2+) was found to be a near-perfect octahedral geometry whereas a distorted octahedral complex was observed in QM/MM. All of the above reasons lead to a different pattern of protein-ligand salt link formation that was not observed in the classical MD simulation. Furthermore to provide a theoretical understanding of inhibition mechanisms of 5CITEP and its derivative (DKA), hybrid QM/MM MD simulations of the two complexes (IN-5CITEP and IN-DKA) have been performed. The results reveal that areas involving residues 60-68, 116-119, and 140-149 were substantially different among the two systems. The two systems show similar pattern of metal coordination geometry, i.e., a distorted octahedron. In IN-DKA, both OD1 and OD2 of Asp-64 coordinate the Mg(2+) in a monodentate fashion whereas only OD1 is chelated to the metal as observed in IN-5CITEP. The high potency of DKA as compared to 5CITEP is supported by a strong salt link formed between its carboxylate moiety and the ammonium group of Lys-159. Detailed comparisons between HIV-1 IN complexed with DKA and with 5CITEP provide information about ligand structure effects on protein-ligand interactions in particular with the Lys-159. This is useful for the design of new selective HIV-1 IN inhibitors.     

Binding mode prediction of biologically active compounds from plant Salvia Miltiorrhiza as integrase inhibitor

Integrase (IN), an essential enzyme for HIV-1 replication, has been targeted in antiretroviral drug therapy. The emergence of HIV-1 variants clinically resistant to antiretroviral agents has lead to the development of alternative IN inhibitors. In the present work, binding modes of a high potent IN inhibitor, M₅22 and M₅32, within the catalytic binding site of wild type (WT) IN were determined using molecular docking calculation. Both M₅22 and M₅32 displayed similar modes of binding within the IN putative binding pocket and exhibited favorable interactions with the catalytic Mg²⁺ ions, the nearby amino acids and viral DNA through metal-ligand chelation, hydrogen bonding and π-π stacking interactions. Furthermore, the modes of action of these two compounds against the mutated Y212R, N224H and S217H PFV IN were also predicted. Although the replacement of amino acid could somehow disturb inhibitor binding mode, almost key interactions which detected in the WT complexes were fairly conserved. Detailed information could highlight the application of M₅22 and M₅32 as candidate IN inhibitors for drug development against drug resistant strains.     

Role of the electrostatic energy between the photo-products and ionic groups on the photoinduced electron transfer rates from aromatic amino acids to the excited flavin in five single-point substitution isoforms of the charged amino acid residue-13 in the FMN-binding protein

Effect of the charge (negative, positive or neutral) of amino acid residue-13 on the photoinduced electron transfer (ET) from Trp32, Tyr35 and Trp106 to the excited isoalloxazine was evaluated in the flavin mononucleotide-binding protein from Desulfovibrio vulgaris isolate Miyazaki F (DvFBP). The protein structures of the wild type and the four isoforms where glutamic acid-13 is replaced with lysine (E13K), arginine (E13R), threonine (E13T) and glutamine (E13Q) in aqueous solution were obtained by molecular dynamics simulation. The distances between the amino acid residue-13 and isoalloxazine (Iso), and between the amino acid residue-13 and the ET donors were longer than 1 nm. The ET rates were evaluated with the Kakitani and Mataga model (KM theory) from their ultrafast fluorescence dynamics by means of a non-linear least squares method. Electrostatic (ES) energies between the photo-products and other ionic groups in the proteins markedly varied among ET donors and among the DvFBP isoforms, while the other physical quantities related to the ET rates, the solvent reorganisation and ES energies between the Iso anion and the donor cations did not vary much between the proteins and donors. A plot of the logarithmic ET rates versus either the total free energy gaps or the net ES energies between the photo-products and the other ionic groups both displayed a parabolic function and so the net ES energies are an important influential factor upon the ET rate, in addition to the donor–acceptor distance.     

Comparison of the monomer structure of the FMN-binding protein from Desulfovibrio vulgaris obtained by NMR and molecular dynamics simulation approaches

Flavin mononucleotide (FMN)-binding proteins (FBPs) play an important role in the electron transport process in bacteria. In this study, the structures of the FBP from Desulfovibrio vulgaris (DvFBP) (Miyazaki F) were compared between those obtained experimentally by nuclear magnetic resonance (NMR) spectroscopy and those derived from molecular dynamics simulations (MDSs). A high-residue root of mean square deviation (RMSD) was observed in residues located at both sides of the wings (Gly22, Glu23, Asp24, Ala59, Arg60, Asp61, Glu62, Gly75, Arg76, Asn77, Gly78 and Pro79), while a low-residue RMSD was found in residues located in a hollow of the structure (Asn12, Glu13, Gly14, Val15, Val16, Asn30, Thr31, Trp32, Asn33, Ser34, Gly69, Ser70, Arg71 and Lys72). Inter-planar angles between the Phe7 and Iso and between the Phe7 and Trp106 residues were remarkably different between the MDS- and NMR-derived DvFBP structures. Distribution of the torsion angles around the covalent bonds in the aliphatic chain of FMN was similar in the MDS- and NMR-derived structures, except for those around the C1′–C2′ and C5′–O5′ bonds. Hydrogen bond formation between IsoO2 and the Gly49 or Gly50 peptide NH was formed in both the NMR- and MDS-derived structures. Overall, the MDS-derived structures were found to be considerably different from the NMR-derived structures, which must be considered when the photoinduced electron transfer in flavoproteins is analysed with MDS-derived structures.     

Molecular prediction of oseltamivir efficiency against probable influenza A (H1N1-2009) mutants: molecular modeling approach

To predict the susceptibility of the probable 2009 influenza A (H1N1-2009) mutant strains to oseltamivir, MD/LIE approach was applied to oseltamivir complexed with the most frequent drug-resistant strains of neuraminidase subtypes N1 and N2: two mutations on the framework residues (N294S and H274Y) and the two others on the direct-binding residues (E119V and R292K) of oseltamivir. Relative to those of the wild type (WT), loss of drug–target interaction energies, especially in terms of electrostatic contributions and hydrogen bonds were dominantly established in the E119V and R292K mutated systems. The inhibitory potencies of oseltamivir towards the WT and mutants were predicted according to the ordering of binding-free energies: WT (−12.3 kcal mol⁻¹) > N294S (−10.4 kcal mol⁻¹) > H274Y (−9.8 kcal mol⁻¹) > E119 V (−9.3 kcal mol⁻¹) > R292K (−7.7 kcal mol⁻¹), suggesting that the H1N1-2009 influenza with R292K substitution, perhaps, conferred a high level of oseltamivir resistance, while the other mutants revealed moderate resistance levels. This result calls for an urgent need to develop new potent anti-influenza agents against the next pandemic of potentially higher oseltamivir-resistant H1N1-2009 influenza.