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Voltage-gated Kv1 potassium channels consist of poreforming ␣ subunits and cytoplasmic Kv␤ subunits. The latter play diverse roles in modulating the gating, stability, and trafficking of Kv1 channels. The crystallographic structure of the Kv␤2 subunit revealed surprising structural homology with aldo-keto reductases, including a triosephosphate isomerase barrel structure, conservation of key catalytic residues, and a bound NADP ؉ cofactor (Gulbis, J. M., Mann, S., and MacKinnon, R. (1999) Cell 90, 943-952). Each Kv1-associated Kv␤ subunit (Kv␤1.1, Kv␤1.2, Kv␤2, and Kv␤3) shares striking amino acid conservation in key catalytic and cofactor binding residues. Here, by a combination of structural modeling and biochemical and cell biological analyses of structure-based mutations, we investigate the potential role for putative Kv␤ subunit enzymatic activity in the trafficking of Kv1 channels. We found that all Kv␤ subunits promote cell surface expression of coexpressed Kv1.2 ␣ subunits in transfected COS-1 cells. Kv␤1.1 and Kv␤2 point mutants lacking a key catalytic tyrosine residue found in the active site of all aldo-keto reductases have wild-type trafficking characteristics. However, mutations in residues within the NADP ؉ binding pocket eliminated effects on Kv1.2 trafficking. In cultured hippocampal neurons, Kv␤ subunit coexpression led to axonal targeting of Kv1.2, recapitulating the Kv1.2 localization observed in many brain neurons. Similar to the trafficking results in COS-1 cells, mutations within the cofactor binding pocket reduced axonal targeting of Kv1.2, whereas those in the catalytic tyrosine did not. Together, these data suggest that NADP ؉ binding and/or the integrity of the binding pocket structure, but not catalytic activity, of Kv␤ subunits is required for intracellular trafficking of Kv1 channel complexes in mammalian cells and for axonal targeting in neurons.

Episodic ataxia type 1 (EA-1) is a neurological disorder arising from mutations in the Kv1.1 potassium channel ␣-subunit. EA-1 patients exhibit substantial phenotypic variability resulting from at least 14 distinct EA-1 point mutations. We found that EA-1 missense mutations generate mutant Kv1.1 subunits with folding and intracellular trafficking properties indistinguishable from wild-type Kv1.1. However, the single identified EA-1 nonsense mutation exhibits intracellular aggregation and detergent insolubility. This phenotype can be transferred to co-assembled Kv1 ␣-and Kv␤-subunits associated with Kv1.1 in neurons. These results suggest that as in many neurodegenerative disorders, intracellular aggregation of misfolded Kv1.1-containing channels may contribute to the pathophysiology of EA-1.