ABSTRACT
Chalcone derivatives of the natural product khellinone were synthesised and screened for bioactivity against the voltage-gated potassium channel Kv1.3. X-ray crystallography was employed to investigate relationships between the structure and function of a selection of the reported chalcones.
Subject(s)
Chalcones/chemical synthesis , Chalcones/pharmacology , Kv1.3 Potassium Channel/antagonists & inhibitors , Potassium Channel Blockers/chemical synthesis , Potassium Channel Blockers/pharmacology , Benzofurans/pharmacology , Chalcones/chemistry , Crystallography, X-Ray , Electrophysiology , Humans , Kv1.3 Potassium Channel/metabolism , Models, Chemical , Molecular Structure , Potassium Channel Blockers/chemistry , Structure-Activity RelationshipABSTRACT
The omega-conotoxins from fish-hunting cone snails are potent inhibitors of voltage-gated calcium channels. The omega-conotoxins MVIIA and CVID are selective N-type calcium channel inhibitors with potential in the treatment of chronic pain. The beta and alpha(2)delta-1 auxiliary subunits influence the expression and characteristics of the alpha(1B) subunit of N-type channels and are differentially regulated in disease states, including pain. In this study, we examined the influence of these auxiliary subunits on the ability of the omega-conotoxins GVIA, MVIIA, CVID and analogues to inhibit peripheral and central forms of the rat N-type channels. Although the beta3 subunit had little influence on the on- and off-rates of omega-conotoxins, coexpression of alpha(2)delta with alpha(1B) significantly reduced on-rates and equilibrium inhibition at both the central and peripheral isoforms of the N-type channels. The alpha(2)delta also enhanced the selectivity of MVIIA, but not CVID, for the central isoform. Similar but less pronounced trends were also observed for N-type channels expressed in human embryonic kidney cells. The influence of alpha(2)delta was not affected by oocyte deglycosylation. The extent of recovery from the omega-conotoxin block was least for GVIA, intermediate for MVIIA, and almost complete for CVID. Application of a hyperpolarizing holding potential (-120 mV) did not significantly enhance the extent of CVID recovery. Interestingly, [R10K]MVIIA and [O10K]GVIA had greater recovery from the block, whereas [K10R]CVID had reduced recovery from the block, indicating that position 10 had an important influence on the extent of omega-conotoxin reversibility. Recovery from CVID block was reduced in the presence of alpha(2)delta in human embryonic kidney cells and in oocytes expressing alpha(1B-b). These results may have implications for the antinociceptive properties of omega-conotoxins, given that the alpha(2)delta subunit is up-regulated in certain pain states.
Subject(s)
Calcium Channels, N-Type/chemistry , Calcium Channels/chemistry , omega-Conotoxins/chemistry , Amino Acid Sequence , Animals , Calcium Channels, N-Type/metabolism , Cell Line , Dose-Response Relationship, Drug , Electrophysiology , Exons , Humans , Kinetics , Magnetic Resonance Spectroscopy , Models, Molecular , Molecular Sequence Data , Oocytes/metabolism , Pain , Peptides/chemistry , Protein Binding , Protein Conformation , Protein Structure, Tertiary , RNA, Complementary/metabolism , Rats , Recombinant Proteins/chemistry , Sequence Homology, Amino Acid , Time Factors , Up-Regulation , Xenopus laevis , omega-Conotoxins/metabolismABSTRACT
Successful uncoating of the influenza B virus in endosomes is predicted to require acidification of the interior of the virus particle. We report that a virion component, the BM2 integral membrane protein, when expressed in Xenopus oocytes or in mammalian cells, causes acidification of the cells and possesses ion channel activity consistent with proton conduction. Furthermore, coexpression of BM2 with hemagglutinin (HA) glycoprotein prevents HA from adopting its low-pH-induced conformation during transport to the cell surface, and overexpression of BM2 causes a delay in intracellular transport in the exocytic pathway and causes morphological changes in the Golgi. These data are consistent with BM2 equilibrating the pH gradient between the Golgi and the cytoplasm. The transmembrane domain of BM2 protein and the influenza A virus A/M2 ion channel protein both contain the motif HXXXW, and, for both proteins, the His and Trp residues are important for channel function.
