Di-substituted cyclohexyl derivatives bind to two identical sites with positive cooperativity on the voltage-gated potassium channel,K(v)1.3

Di-substituted cyclohexyl (DSC) derivatives inhibit the voltage-gated potassium channel, K(v)1.3, and have immunosuppressant activity (Schmalhofer et al. (2002) Biochemistry 41, 7781-7794). This class of inhibitors displays Hill coefficients of near 2 in functional assays, and trans DSC analogues appear to selectively interact with K(v)1.3 channel conformations related to C-type inactivation. To further understand the details of the DSC inhibitor interaction with potassium channels, trans-1-(N-n-propylcarbamoyloxy)-4-phenyl-4-(3-(2-methoxyphenyl)-3-oxo-2-azaprop-1-yl)cyclo-hexane (trans-NPCO-DSC) was radiolabeled with tritium, and its binding characteristics to K(v)1.3 channels were determined. Specific binding of [(3)H]-trans-NPCO-DSC to K(v)1.3 channels is a saturable, time-dependent, and fully reversible process. Saturation binding isotherms and competition binding experiments are consistent with the presence of two receptor sites for DSC derivatives on the K(v)1.3 channel that display positive allosteric cooperativity. The high affinity interaction of [(3)H]-trans-NPCO-DSC with K(v)1.3 channels appears to correlate with the rates of C-type inactivation of the channel. These data, taken together, mark the first demonstration of the existence of multiple binding sites for an inhibitor of an ion channel and suggest that the high affinity interaction of trans-NPCO-DSC and similar inhibitors with K(v)1.3 channels could be exploited for the development of selective molecules that target this protein.     

Article Watch: July 2015

This column highlights recently published articles that are of interest to the readership of this publication. We encourage ABRF members to forward information on articles they feel are important and useful to Clive Slaughter, Georgia Regents University-University of Georgia Medical Partnership, 1425 Prince Ave., Athens, GA 30606, USA. Phone: 706-713-2216; Fax: 706-713-2221; E-mail: ude.agu@thgualsc; or to any member of the Editorial Board. Article summaries reflect the reviewer’s opinions and not necessarily those of the association.     

Evolution by leaps: gene duplication in bacteria

Background  

Sequence related families of genes and proteins are common in bacterial genomes. In Escherichia coli they constitute over half of the genome. The presence of families and superfamilies of proteins suggest a history of gene duplication and divergence during evolution. Genome encoded protein families, their size and functional composition, reflect metabolic potentials of the organisms they are found in. Comparing protein families of different organisms give insight into functional differences and similarities.     

Properties of a Glutamatergic Synapse Controlling Information Output from Retinal Bipolar Cells

One general categorization of retinal ganglion cells is to segregate them into tonically or phasically responding neurons, each conveying discrete aspects of the visual scene. Although best identified in the output signals of the retina, this distinction is initiated at the first synapse: between photoreceptors and the dendrites of bipolar cells. In this study we found that the output synapses of bipolar cells also contribute to separate these pathways. Both transient and sustained ganglion cells can produce maintained spike activity, but bipolar cell glutamate release exhibits a divergence that corresponds to the response characteristics of the ganglion cells. Comparing light intensity coding in the sustained and transient ON pathways revealed that they shared the intensity spectrum. The transient pathway had greater sensitivity but smaller dynamic range, and switched from intensity coding to event detection at light levels where sustained pathway sensitivity began to rise. The distinctive properties of the sustained pathway depended upon inhibition and shifted toward those of the transient pathway in the absence of inhibition. The transient system was comparatively unaffected by the loss of inhibition and this was due to the concomitant activation of perisynaptic NMDA receptors. Overall, the properties of bipolar cell dendritic and axon terminals both contribute to the formation of key aspects of the sustained/transient dichotomy normally associated with ganglion cells.     

Biosynthesis of flavour-active furanones by Saccharomyces cerevisiae during fermentation depends on the malt type used in medium preparation

Extracts of a coloured malt contained 4-hydroxy-5-monomethyl-3(2H)-furanone (HMMF), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) but not 4-hydroxy-5(or 2)-ethyl-2(or 5)-methyl-3(2H)-furanone (HEMF). Extracts of a pale malt did not contain any of the furanones. HMMF and HDMF were produced by Saccharomyces cerevisiae during fermen-tation of both types of malt extract. About 0.09 mg HEMF l ⁻¹ was synthesised during fermentation of the coloured malt extract but none was produced with the pale malt extract. Final concentrations of HDMF (2.0 mgl ⁻¹) and HEMF (0.09 mgl ⁻¹) were in excess of their aroma threshold values in water (0.16 and 0.02 mgl ⁻¹ respectively) after fermen-tation of the coloured malt extract. This revised version was published online in November 2006 with corrections to the Cover Date.     

Critical role of amyloid-like oligomers of Drosophila Orb2 in the persistence of memory

A long-standing question in the study of long-term memory is how a memory trace persists for years when the proteins that initiated the process turn over and disappear within days. Previously, we postulated that self-sustaining amyloidogenic oligomers of cytoplasmic polyadenylation element-binding protein (CPEB) provide a mechanism for the maintenance of activity-dependent synaptic changes and, thus, the persistence of memory. Here, we found that the Drosophila CPEB Orb2 forms amyloid-like oligomers, and oligomers are enriched in the synaptic membrane fraction. Of the two protein isoforms of Orb2, the amyloid-like oligomer formation is dependent on the Orb2A form. A point mutation in the prion-like domain of Orb2A, which reduced amyloid-like oligomerization of Orb2, did not interfere with learning or memory persisting up to 24?hr. However the mutant flies failed to stabilize memory beyond 48?hr. These results support the idea that amyloid-like oligomers of neuronal CPEB are critical for the persistence of long-term memory.     

Cell-cycle-coupled structural oscillation of centromeric nucleosomes in yeast

The centromere is a specialized chromosomal structure that regulates chromosome segregation. Centromeres are marked by a histone H3 variant. In budding yeast, the histone H3 variant Cse4 is present in a single centromeric nucleosome. Experimental evidence supports several different models for the structure of centromeric nucleosomes. To investigate Cse4 copy number in live yeast, we developed a method coupling fluorescence correlation spectroscopy and calibrated imaging. We find that centromeric nucleosomes have one copy of Cse4 during most of the cell cycle, whereas two copies are detected at anaphase. The proposal of an anaphase-coupled structural change is supported by Cse4-Cse4 interactions, incorporation of Cse4, and the absence of Scm3 in anaphase. Nucleosome reconstitution and ChIP suggests both Cse4 structures contain H2A/H2B. The increase in Cse4 intensity and deposition at anaphase are also observed in Candida albicans. Our experimental evidence supports a cell-cycle-coupled oscillation of centromeric nucleosome structure in yeast.