The roles of N- and C-terminal determinants in the activation of the Kv2.1 potassium channel

The human and rat forms of the Kv2.1 channel have identical amino acids over the membrane-spanning regions and differ only in the N- and C-terminal intracellular regions. Rat Kv2.1 activates much faster than human Kv2.1. Here we have studied the role of the N- and C-terminal residues that determine this difference in activation kinetics between the two channels. For this, we constructed mutants and chimeras between the two channels, expressed them in oocytes, and recorded currents by two-electrode voltage clamping. In the N-terminal region, mutation Q67E in the rat channel displayed a slowing of activation relative to rat wild type, whereas mutation D75E in the human channel showed faster activation than human wild type. In the C-terminal region, we found that some residues within the region of amino acids 740-853 ("CTA" domain) were also involved in determining activation kinetics. The electrophysiological data also suggested interactions between the N and C termini. Such an interaction was confirmed directly by using a glutathione S-transferase (GST) fusion protein with the N terminus of Kv2.1, which we showed to bind to the C terminus of Kv2.1. Taken together, these data suggest that exposed residues in the T1 domain of the N terminus, as well as the CTA domain in the C terminus, are important in determining channel activation kinetics and that these N- and C-terminal regions interact.