The long-term objective of this research is to develop an understanding of the underlying cellular events and mechanisms involved in mutations in ion channel disorders. Mutations in Kv1.1 potassium (K+) channel coding regions cause the autosomal dominant disorder episodic ataxia type-1 (EA-1) in humans. Possible mechanisms include abnormalities in protein stability, trafficking to the cell surface, or functional expression or combinations of these parameters, including dominant-negative effects. We, and others, have characterized a number of these mutants and mechanistic insights have been suggested for some of them. In this study Kv1.1 and EA-1 mutants are expressed in tissue culture cell lines and a combination of approaches are used to determine the effect of EA-1 mutations on the channel's protein stability, trafficking, cell surface protein expression levels, and cell surface conductance density levels. Additional electrophysiological characterization is performed on selected mutants. Given that most EA-1 mutations are radical substitutions that occur in highly conserved transmembrane segments, we propose that most mutations will cause a decrease in protein stability due to protein misfolding. In addition, coexpression studies with another Kv11 subunit will be done. This approach will reveal in greater detail the underlying cellular events and mechanisms involved in EA-1 mutations. The different EA-1 mutants can then be tentatively assigned to different dysfunctional classes (e.g. protein stability problem, trafficking problem, and/or functional problem). To gain further insights into why each radical amino acid substitution causes channel dysfunction, we will also test the effects of conservative replacements at these EA-1 positions.
The relevance of this study is that the mechanisms uncovered here will be helpful in assigning possible therapeutic approaches to treat a neurological disorder. This research should also be relevant to other disorders caused by mutations in channel genes.
