Allosteric pocket of the dengue virus (serotype 2) NS2B/NS3 protease: In silico ligand screening and molecular dynamics studies of inhibition.

The allosteric pocket of the Dengue virus (DENV2) NS2B/NS3 protease, which is proximal to its catalytic triad, represents a promising drug target (Othman et al., 2008). We have explored this binding site through large-scale virtual screening and molecular dynamics simulations followed by calculations of binding free energy. We propose two mechanisms for enzyme inhibition. A ligand may either destabilize electronic density or create steric effects relating to the catalytic triad residues NS3-HIS51, NS3-ASP75, and NS3-SER135. A ligand may also disrupt movement of the C-terminal of NS2B required for inter-conversion between the "open" and "closed" conformations. We found that chalcone and adenosine derivatives had the top potential for drug discovery hits, acting through both inhibitory mechanisms. Studying the molecular mechanisms of these compounds might be helpful in further investigations of the allosteric pocket and its potential for drug discovery.

Molecular dynamics study of hell's gate globin I (HGbI) from a methanotrophic extremophile: oxygen migration through a large cavity.

Hell's gate globin I (HGbI), a heme-containing protein from the extremophile Methylacidiphilum infernorum, has fast oxygen-binding/slow release characteristics due to its distal residues Gln and Tyr. The combination of Gln/Tyr distal iron coordination, adaptation to extreme environmental conditions, and lack of a D helix suggests that ligand migration in HGbI differs from other previously studied globins. Locally enhanced molecular dynamics trajectories of oxygen migration indicate a large internal cavity. This may increase the tendency of oxygen to exit from portals other than the most direct exit from the space near the heme. Oxygen may reside transiently in shallow surface depressions around the exits. Such surface trapping may enhance both oxygen uptake by increasing contact time between molecules, and decrease release by increasing the probability of oxygen reentry from the vicinity of the portal.

Mechanism of glycan receptor recognition and specificity switch for avian, swine, and human adapted influenza virus hemagglutinins: a molecular dynamics perspective.

Hemagglutinins (HA's) from duck, swine, and human influenza viruses have previously been shown to prefer avian and human glycan receptor analogues with distinct topological profiles, pentasaccharides LSTa (alpha-2,3 linkage) and LSTc (alpha-2,6 linkage), in comparative molecular dynamics studies. On the basis of detailed analyses of the dynamic motions of the receptor binding domains (RBDs) and interaction energy profiles with individual glycan residues, we have identified approximately 30 residue positions in the RBD that present distinct profiles with the receptor analogues. Glycan binding constrained the conformational space sampling by the HA. Electrostatic steering appeared to play a key role in glycan binding specificity. The complex dynamic behaviors of the major SSE and trimeric interfaces with or without bound glycans suggested that networks of interactions might account for species specificity in these low affinity and high avidity (multivalent) interactions between different HA and glycans. Contact frequency, energetic decomposition, and H-bond analyses revealed species-specific differences in HA-glycan interaction profiles, not readily discernible from crystal structures alone. Interaction energy profiles indicated that mutation events at the set of residues such as 145, 156, 158, and 222 would favor human or avian receptor analogues, often through interactions with distal asialo-residues. These results correlate well with existing experimental evidence, and suggest new opportunities for simulation-based vaccine and drug development.

Distinct glycan topology for avian and human sialopentasaccharide receptor analogues upon binding different hemagglutinins: a molecular dynamics perspective.

Hemagglutinin (HA) binds to sialylated glycans exposed on the host cell surface in the initial stage of avian influenza virus infection. It has been previously hypothesized that glycan topology plays a critical role in the human adaptation of avian flu viruses, such as the potentially pandemic H5N1. Comparative molecular dynamics studies are complementary to experimental techniques, including glycan microarray, to understand the mechanism of species-specificity switch better. The examined systems comprise explicitly solvated trimeric forms of avian H3, H5, and swine H9 in complex with avian and human glycan receptor analogues--LSTa (alpha-2,3-linked lactoseries tetrasaccharide a) and LSTc (alpha-2,6-linked lactoseries tetrasaccharide c), respectively. The glycans adopted distinct topological profiles with inducible torsional angles when bound to different HAs. The corresponding receptor binding domain amino acid contact profiles were also distinct. Avian H5 was able to accommodate LSTc in a tightly "folded umbrella"-like topology through interactions with all five sugar residues. After considering conformational entropy, the relative binding free-energy changes, calculated using the molecular mechanics-generalized Born surface area technique, were in agreement with previous experimental findings and provided insights on electrostatic, van der Waals, desolvation, and entropic contributions to HA-glycan interactions. The topology profile and the relative abundance of free glycan receptors may influence receptor binding kinetics. Glycan composition and topological changes upon binding different HAs may be important determinants in species-specificity switch.

Docking of noncompetitive inhibitors into dengue virus type 2 protease: understanding the interactions with allosteric binding sites.

A group of flavanones and their chalcones, isolated from Boesenbergia rotunda L., were previously reported to show varying degrees of noncompetitive inhibitory activities toward Dengue virus type 2 (Den2) protease. Results obtained from automated docking studies are in agreement with experimental data in which the ligands were shown to bind to sites other than the active site of the protease. The calculated K(i) values are very small, indicating that the ligands bind quite well to the allosteric binding site. Greater inhibition by pinostrobin, compared to the other compounds, can be explained by H-bonding interaction with the backbone carbonyl of Lys74, which is bonded to Asp75 (one of the catalytic triad residues). In addition, structure-activity relationship analysis yields structural information that may be useful for designing more effective therapeutic drugs against dengue virus infections.

Altered levels of hypothalamic-pituitary-adrenocortical axis hormones in baboons and mice during the course of infection with Schistosoma mansoni.

Baboons with primary or secondary exposure to Schistosoma mansoni were compared with each other over a 12-week infection period and with baseline values obtained from uninfected baboons with respect to serum levels of the hypothalamic-pituitary-adrenal (HPA) axis hormones-corticotropin-releasing hormone, adrenocorticotropic hormone, dehydroepiandrosterone sulfate (DHEA-S), and cortisol. Baboons with primary infections, when worm recovery and oviposition rates were high and hepatic schistosome egg granulomas were large, had decreasing levels of these hormones as infection progressed, compared with both uninfected and reexposed baboons. The most reduced hormone level was that of DHEA-S. Reduction of DHEA-S and cortisol levels also occurred in primary murine infections. Reexposed baboons with low worm recovery and oviposition rates and small (modulated) hepatic granulomas showed the opposite pattern: HPA axis hormone levels were maintained at, or exceeded, the baseline values of uninfected baboons. These results suggest that HPA axis hormones may play a role in regulating the establishment, maturation, and oviposition of schistosomes and the progression of schistosomiasis.

Fatal hyperthermia in a quadriplegic man. Possible evidence for a peripheral action of haloperidol in neuroleptic malignant syndrome.

A patient with a cervical cord transection isolating his hypothalamic thermoregulatory centers from peripheral effectors suffered a fatal hyperthermic episode after receiving haloperidol. This suggests that neuroleptic malignant syndrome is caused by a peripheral, not central, effect of haloperidol.