Interacting Slowpoke Channel Subunits

Abstract

Many ion channels consist of a pore-forming subunit along with other associated subunits and regulatory proteins that can modulate localization of the channel, its stability, and many aspects of channel conductance. These interactions are usually considered in terms of effects of the auxiliary subunits on the activity of the pore-forming subunit, but Jin et al. point out that reciprocal effects are potentially important in these protein-protein interactions. The h Slo (human slowpoke) large-conductance Ca 2+ -dependent K channels contribute to action potential repolarization in neurons and modulate neurotransmitter release. The pore-forming α subunit of these channels is regulated by a family of β subunits. Jin et al. show that the β4 subunit expressed in HEK 293 cells is multiply glycosylated and that full glycosylation can be observed only when the α subunit is also expressed. Glycosylation of the β4 subunit in turn modulates its effect on the α subunit. One action of the β4 subunit is to protect the channel from inhibition by iberiotoxin. But this effect is lost when the β4 subunit is fully glycosylated. Although it remains to be established whether there are physiological repercussions of the changes revealed by monitoring toxin sensitivity, the authors note that it may be important to consider such two-way communication between subunits to fully understand mechanisms that regulate channel conductance. P. Jin, T. M. Weiger, I. B. Levitan, Reciprocal modulation between the α and β4 subunits of h Slo calcium-dependent potassium channels. J. Biol. Chem. 277 , 43724-43729 (2002). [Abstract] [Full Text]