| The cloning of the mammalian Kv1 K+ channel beta-subunit has provided a means of studying the native oligomeric structure of K+ channels in Xenopus oocytes and transfected mammalian cells. I investigated the effect of the Kvbeta2 subunit on various Kv1 K+ channels in Xenopus oocytes. I observed that Kvbeta2 was able to enhance the current amplitude of Kv1.4 more than twofold, and that Kvbeta2 was able to accelerate the inactivation of Kv1.4, the first report of functional effects of Kvbeta2.;It has been shown that, like Kv1.3-mediated K+ current, transcription and protein levels of murine Kvbeta1 and beta2 are increased in T-lymphocytes stimulated by IL2 (Autieri, 1997). I investigated the effect of Kvbeta2 on Kv1.3 channels. I observed that Kvbeta2 was able to enhance the current amplitudes of Kv1.3 fourfold in Xenopus oocytes. Since it has been shown that beta-subunits facilitate proper alpha-subunit targeting to the membrane, a possible explanation for enhanced Kv1.3 currents in activated T-lymphocytes without an increase in Kv1.3 mRNA levels is that the beta-subunits mediate an increase in membrane targeting of K+ channels. Western blot analysis shows that the Kvbeta2 protein levels are not enhanced in activated human T-cells, providing a potential explanation for the differences in the changes in K+ conductances that occur upon activation in mouse versus human T-cells.;I show that the Shaker beta-subunits belong to the aldo-keto reductase superfamily, a group of proteins which reduce/oxidize a wide range of physiologic substrates. The Shaker beta-subunits belong to a discrete branch of this protein superfamily which also includes the Drosophila Hyperkinetic protein. I constructed a putative structure for the beta-subunit based on the structure of aldose reductase, an aldo-keto reductase enzyme whose structure has been determined by X-ray crystallography. Sequence analysis revealed that the vast majority of cofactor binding residues of the aldose reductase protein are conserved in the beta-subunits. A Kvbeta2 point mutation of a conserved tyrosine, the crucial catalytic residue among the aldo-keto reductase enzymes, to phenylalanine, results in a protein which can still enhance current amplitudes and accelerate the inactivation of Kv1.4, ruling out catalysis as the mechanism by which these effects occur. |
