Transporter viral inhibitors

It is likely that other unique viral inhibitors of TAP will be defined, including early proteins derived from bovine herpes virus BHVl (Hinkley et al. 1998) and pseudorabies virus (Ambagala et al. 2000). These will not only result in recognition of the strategies viruses use to hide for the immune system but will also provide a flow of information on the mechanism of action of the peptide transporter TAP. 

A successful tool in the early studies of metabolic pathways was blocking the pathway at some specific point. This could be done by the use of either mutants or inhibitors. Schekman et al have isolated a number of yeast mutants with blocks in their secretion pathway (Schekman, 1982). It is not yet known which proteins these mutations affect, but this is clearly a most promising approach for identifying those components involved in transport. In animal cells there are no cellular mutants with blocks in the intracellular transport of protein from the ER to the cell surface. There are, however, genetic diseases which affect the routing of lysosomal enzymes to the lysosomes (Neufeld et al, 1975 Sly and Fischer, 1982). For viruses it has been possible to isolate temperature-sensitive mutants in which a mutation in the viral glycoprotein arrests... 

All the nearest-neighbor interactions between sialic acid or Neu5Ac2en and the protein are with totally conserved amino acids. Thus an inhibitor designed to bind only to the conserved active-site residues of neuraminidase would inhibit neuraminidase activity across all strains of influenza. This would enable the development of an antiviral drug that would affect the spread of viral replication potentially in three ways, i.e., transport through the protective mucosal layer, desialyation of freshly synthesized viral glycoproteins, and elution of progeny virions from infected cells. 

Didanosine is a synthetic purine nucleoside analog that inhibits the activity of reverse transcriptase in HIV-1, HIV-2, other retroviruses and zidovudine-resistant strains. A nucleobase carrier helps transport it into the cell where it needs to be phosphorylated by 5 -nucleoiidase and inosine 5 -monophosphate phosphotransferase to didanosine S -monophosphate. Adenylosuccinate synthetase and adenylosuccinate lyase then convert didanosine 5 -monophosphate to dideoxyadenosine S -monophosphate, followed by its conversion to diphosphate by adenylate kinase and phosphoribosyl pyrophosphate synthetase, which is then phosphorylated by creatine kinase and phosphoribosyl pyrophosphate synthetase to dideoxyadenosine S -triphosphate, the active reverse transcriptase inhibitor. Dideoxyadenosine triphosphate inhibits the activity of HIV reverse transcriptase by competing with the natural substrate, deoxyadenosine triphosphate, and its incorporation into viral DNA causes termination of viral DNA chain elongation. It is 10-100-fold less potent than zidovudine in its antiviral activity, but is more active than zidovudine in nondividing and quiescent cells. At clinically relevant doses, it is not toxic to hematopoietic precursor cells or lymphocytes, and the resistance to the drug results from site-directed mutagenesis at codons 65 and 74 of viral reverse transcriptase. 

The brain needs the influx of nucleosides because the brain is deficient in de novo nucleotide synthesis (102). Purine and pyrimidine nucleosides are necessary for the synthesis of DNA and RNA, but nucleosides also influence many other biological processes. In addition, nucleosides play an important role in the treatment of diseases, such as cardiac diseases, brain cancers, and infections [parasitic and viral (103)]. Nucleosides are hydrophilic compounds, and the influx and efflux of these compounds is therefore mediated by a number of distinct transporters (104). Nucleoside transporters are membrane-fixed transporters and are classified by their transport mechanisms (e = equilibrative, c = concentrative), their sensitivity to the transport inhibitor nitrobenzylmercaptopurine riboside (NBMPR s = sensitive, i = insensitive), and their substrates. Presently, there are two equilibrative transporters (ENTs es and ei) and six concentrative nucleoside transporters [CNTs cif (concentrative, NBMPR insensitive, broad specificity Nl), cit (concentrative, NBMPR insensitive, common permeant thymidine N2), cib (concentrative, NBMPR insensitive, broad specificity N3), cib (concentrative, MBMPR insensitive, broad specificity N4), cs (concentrative, NBMPR sensitive N5), and csg (concentrative, NBMPR sensitive, accepts guanosine as permeant N6) (104)]. The equilibrative es and ei nucleoside transporters are widely expressed in mammalian cells and are present at cultured endothelial cells and brain capillaries (105). In these cells, the expression of concentrative transporter cit (N2) was demonstrated also. In other parts of the rat brain, ei and es nucleoside transport systems have... 

In normal cells, ion transport is regulated by the Na /K" -dependent ATPase (sodium pump Dahl and Hokin, 1974). Inhibition of the sodium pump should result in alteration of ionic environment inside infected cells. To test this hypothesis further, Garry et al. (1919b) studied the effect of ouabain, a specific inhibitor of the sodium pump. At a concentration of ouabain which inhibited protein synthesis in uninfected cells by 95% or more, viral protein synthesis was not affected. Ouabain treatment raises the intracellular Na ion concentration and simultaneously decreases the intracellular ion concentration of uninfected cells. The effect of SIN virus infection is similar to that of ouabain treatment, suggesting that the sodium pump is indeed inhibited by virus infection. 

Biological Applications Chloride channel blockers anion transport inhibitors treating can-cer, glaucoma, heart diseases, viral diseases Industrial Applications Not reported Safety/Toxici Effect on hemolysis lysosomal sulfate transport ... 

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