Copper adsorption onto calcium alginate encapsulated magnetic sorbent is studied in this paper. The objective of this study was to qualitatively and quantitatively elucidate the copper binding onto the sorbent. The adsorption increases from around 0 to almost 100% as the initial pH is increased from 2 to 5. A maximum adsorption capacity of 0.99 mmol g -1 is achieved. The FT-IR and XPS studies show that the CsO in carboxyl group of alginate directly attaches to the copper ion that leads to most of the adsorption. A mathematical model is developed, and it includes ion exchange between the calcium and the copper, coordination reaction between the functional group and the copper, as well as surface complex formation between the iron oxide and the copper. The model is capable of describing and predicting effects of various key operational parameters on the adsorption process, such as initial pH, metal concentration, and dosage of sorbent.
Chronic infection by hepatitis C virus (HCV) can lead to severe hepatitis and cirrhosis and is closely associated with hepatocellular carcinoma. The replication cycle of HCV is poorly understood but is likely to involve interaction with host factors. In this report, we show that NS5B, the HCV RNA-dependent RNA polymerase (RdRp), interacts with a human RNA helicase, p68. Transient expression of NS5B alone, as well as the stable expression of all the nonstructural proteins in a HCV replicon-bearing cell line (V. Lohmann, F. Korner, J.-O. Koch, U. Herian, L. Theilmann, and R. Bartenschlager, Science 285:110-113), causes the redistribution of endogenous p68 from the nucleus to the cytoplasm. Deletion of the C-terminal two-thirds of NS5B (NS5B⌬C) dramatically reduces its coimmunoprecipitation (co-IP) with endogenous p68, while the deletion of the Nterminal region (NS5B⌬N1 and NS5B⌬N2) does not affect its interaction with p68. In consistency with the co-IP results, NS5B⌬C does not cause the relocalization of p68 whereas NS5B⌬N1 does. With a replicon cell line, we were not able to detect a change in positive-and negative-strand synthesis when p68 levels were reduced using small interfering RNA (siRNA). In cells transiently transfected with a full-length HCV construct, however, the depletion (using specific p68 siRNA) of endogenous p68 correlated with a reduction in the transcription of negative-strand from positive-strand HCV RNA. Overexpression of NS5B and NS5B⌬N1, but not that of NS5B⌬C, causes a reduction in the negative-strand synthesis, indicating that overexpressed NS5B and NS5B⌬N1 sequesters p68 from the replication complexes (thus reducing their replication activity levels). Identification of p68 as a cellular factor involved in HCV replication, at least for cells transiently transfected with a HCV expression construct, is a step towards understanding HCV replication.Hepatitis C virus (HCV) is a positive-stranded RNA virus belonging to the family Flaviviridae. It infects more than 170 million people worldwide and poses an important medical problem in developed and underdeveloped countries. HCV replicates in the liver, and chronic infection often leads to cirrhosis, steatosis, and hepatocellular carcinoma. Practically all processes in the life cycle of viruses, including viral entry, translation, processing and modification of viral proteins, maturation, and release of viral particles from host cells, are dependent on the host cell machinery and involve intimate interaction between viral and host proteins. The role of host proteins in the replication cycle of HCV and the effect of virus-host interaction have remained poorly understood. This is due to a lack of cell culture and animal model systems for studying the biology of this virus. The study of the interaction of HCV with cellular proteins has been limited to the identification of host proteins interacting with individual viral proteins.The proteins encoded by the HCV genome are three structural proteins (core protein and envelope proteins E1 and E2) and se...
Fragment-based docking was used to select a conformation for virtual screening from a molecular dynamics trajectory of the West Nile virus nonstructural 3 protease. This conformation was chosen from an ensemble of 100 molecular dynamics snapshots because it optimally accommodates benzene, the most common ring in known drugs, and two positively charged fragments (methylguanidinium and 2-phenylimidazoline). The latter fragments were used as probes because of the large number of hydrogen bond acceptors in the substrate binding site of the protease. Upon high-throughput docking of a diversity set of 18,694 molecules and pose filtering, only five compounds were chosen for experimental validation, and two of them are active in the low micromolar range in an enzymatic assay and a tryptophan fluorescence quenching assay. Evidence for specific binding to the protease active site is provided by nuclear magnetic resonance spectroscopy. The two inhibitors have different scaffolds (diphenylurea and diphenyl ester) and are promising lead candidates because they have a molecular weight of about 300 Da.
The Flavivirus NS5 protein possesses both (guanine-N7)-methyltransferase and nucleoside-2 -O methyltransferase activities required for sequential methylation of the cap structure present at the 5 end of the Flavivirus RNA genome. Seventeen mutations were introduced into the dengue virus type 2 NS5 methyltransferase domain, targeting amino acids either predicted to be directly involved in S-adenosyl-L-methionine binding or important for NS5 conformation and/or charged interactions. The effects of the mutations on (i) (guanine-N7)-methyltransferase and nucleoside-2 -O methyltransferase activities using biochemical assays based on a bacterially expressed NS5 methyltransferase domain and (ii) viral replication using a dengue virus type 2 infectious cDNA clone were examined. Clustered mutations targeting the S-adenosyl-L-methionine binding pocket or an active site residue abolished both methyltransferase activities and viral replication, demonstrating that both methyltransferase activities utilize a single S-adenosyl-L-methionine binding pocket. Substitutions to single amino acids binding S-adenosyl-L-methionine decreased both methyltransferase activities by varying amounts. However, viruses that replicated at wild type levels could be recovered with mutations that reduced both activities by >75%, suggesting that only a threshold level of methyltransferase activity was required for virus replication in vivo. Mutation of residues outside of regions directly involved in S-adenosyl-L-methionine binding or catalysis also affected methyltransferase activity and virus replication. The recovery of viruses containing compensatory second site mutations in the NS5 and NS3 proteins identified regions of the methyltransferase domain important for overall stability of the protein or likely to play a role in virus replication distinct from that of cap methylation.Cellular and many viral mRNAs contain a modified 5Ј-terminal guanosine "cap" structure covalently linked to the 5Ј end of the mRNA. The study of mRNA cap formation using viral, eukaryotic, and protozoan systems has shown that the formation of the 5Ј-RNA cap structure requires three sequential enzymatic reactions. First, the 5Ј-terminal triphosphate of the nascent RNA is hydrolyzed to a diphosphate by the enzyme RNA triphosphatase. Second, the RNA is capped with GMP in a 5Ј-5Ј triphosphate linkage by mRNA guanyltransferase, and third, the guanosine is methylated at the N 7 position by a (guanine-N7)-methyltransferase (N7 MTase) 2 using S-adenosyl-Lmethionine (AdoMet) as a methyl donor to form a type 0 ( 7Me G 5Ј -ppp 5Ј N) cap structure (1, 2). Nucleotides adjacent to the cap structure may be further methylated by nucleoside-2Ј-O methyltransferases (2Ј-O MTase) to give type I ( 7Me G 5Ј -ppp 5Ј N Me ) or type II cap structures ( 7Me G 5Ј -ppp 5Ј N Me N Me ). In the simplest case, such as for yeast, each of the enzymatic activities required for RNA capping resides in an individual protein. However, studies on viral capping systems have revealed many interesting variations o...
The adsorption of organic arsenate, monomethylarsonate (MMA), onto a calcium alginate encapsulated magnetic sorbent is studied in this paper. A novel alginate encalsulated magnetic sorbent was used in the experiments on adsorption isotherm, kinetics, and pH effect. It was found that the equilibrium sorption can be attained within 25 h. Solution pH plays a key role in the removal of MMA from the solution. A greater adsorption can be achieved at pH 4 and below. The maximum sorption capacity of MMA was 8.57 mg As/g, which is slightly higher than the reported adsorbents. The interaction characteristics between the organic arsenate and magnetic sorbent were elucidated by applying FT-IR and XPS analyses. It is shown that the -COOH and Fe-O groups in the sorbent are involved in the adsorption process. The appearance of As-CH(3) and alkane C-H groups in the FT-IR spectrum reveals the binding of the organic arsenate to the sorbent. The XPS analysis indicates that reduction of organic arsenate to organic arsenite on the sorbent's surface happens through solid state redox reaction via charge transport from Fe(II) and C-O species in the sorbent. The XPS results also show the disappearance of C-OH and formation of As-O. It is deduced from the spectral results that mechanisms of organic arsenate adsorption involve C-OH, As-O, and Fe-O groups with the solid state redox process.
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