Abstract
The cloning and characterization of the voltage-activated Shaker potassium channel gene in Drosophila have led to the identification of structural elements involved in potassium channel gating. As found for the voltage-activated sodium channel, the S4 segment, located in the conserved core of the protein, plays a central role in voltage-dependent activation. Potassium channels appear to be formed by the assembly of several polypeptides into multisubunit channels. This is directly analogous to the proposed folding of the four internally homologous pseudosubunits of sodium and calcium channels. The amino- and carboxy-terminal regions of Shaker channels are specialized for, and appear to interact in, inactivation gating. This interaction probably includes interaction between subunits, as may be said for the role in inactivation gating of the junction between the carboxyl terminus of the third domain and amino terminus of the fourth domain of sodium channel (Vassilev et al. 1988). The capacity for coassembly in potassium channels extends not only to the alternatively spliced products of the same gene, but also to the products of different genes. Heteromultimeric channels that are formed in this way have kinetic and pharmacological properties that differ from homomultimers of their constituents and, as such, broaden the functional diversity of channels that can be produced by any given number of compatible potassium channel genes.
