Intracellular regions of potassium channels: Kv2.1 and heag

Abstract

Intracellular regions of voltage-gated potassium channels often comprise the largest part of the channel protein, and yet the functional role of these regions is not fully understood. For the Kv2.1 channel, although there are differences in activation kinetics between rat and human channels, there are, for instance, no differences in movement of the S4 region between the two channels, and indeed our mutagenesis studies have identified interacting residues in both the N- and C -terminal intracellular regions that are responsible for these functional effects. Furthermore, using FRET with fluorescent-tagged Kv2.1 channels, we have shown movement of the C-termini relative to the N-termini during activation. Such interactions and movements of the intracellular regions of the channel appear to form part of the channel gating machinery. Heag1 and heag2 channels also display differing activation properties, despite their considerable homology. By a chimeric approach, we have shown that these differences in activation kinetics are determined by multiple interacting regions in the N-terminus and membrane-spanning regions. Furthermore, alanine mutations of many residues in the C-terminal cyclic nucleotide binding domain affect activation kinetics. The data again suggest interacting regions between N- and C- termini that participate in the conformational changes during channel activation. Using a mass-spectrometry approach, we have identified alpha-tubulin and a heat shock protein as binding to the C-terminus of the heag2 channel, and alpha-tubulin itself has functional effects on channel activation kinetics. Clearly, the intracellular regions of these ion channels (and most likely many other ion channels too) are important regions in determining channel function.