Inactivation of a voltage-dependent K+ channel by beta subunit. Modulation by a phosphorylation-dependent interaction between the distal C terminus of alpha subunit and cytoskeleton.
Kv1.1/Kvbeta1.1 (alphabeta) K+ channel expressed in Xenopus oocytes was shown to have a fast inactivating current component. The fraction of this component (extent of inactivation) is increased by microfilament disruption induced by cytochalasins or by phosphorylation of the alpha subunit at Ser-446, which impairs the interaction of the channel with microfilaments. The relevant sites of interaction on the channel molecules have not been identified. Using a phosphorylation-deficient mutant of alpha, S446A, to ensure maximal basal interaction of the channel with the cytoskeleton, we show that one relevant site is the end of the C terminus of alpha. Truncation of the last six amino acids resulted in alphabeta channels with an extent of inactivation up to 2.5-fold larger and its further enhancement by cytochalasins being reduced 2-fold. The wild-type channels exhibited strong inactivation, which could not be markedly increased either by cytochalasins or by the C-terminal mutations, indicating that the interaction of the wild-type channels with microfilaments was minimal to begin with, presumably because of extensive basal phosphorylation. Since the C-terminal end of Kv1.1 was shown to participate in channel clustering via an interaction with members of the PSD-95 family of proteins, we propose that a similar interaction with an endogenous protein takes place, contributing to channel connection to the oocyte cytoskeleton. This is the first report to assign a modulatory role to such an interaction: together with the state of phosphorylation of the channel, it regulates the extent of inactivation conferred by the beta subunit.
Jing
J
J
Department of Physiology and Pharmacology, Sackler School of Medicine, Tel-Aviv University, 69978 Ramat Aviv, Israel.
Peretz
T
T
Singer-Lahat
D
D
Chikvashvili
D
D
Thornhill
W B
WB
Lotan
I
I
D000595:Amino Acid Sequence; D000818:Animals; D003599:Cytoskeleton / Q000502:physiology*; D005260:Female; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D010766:Phosphorylation; D015221:Potassium Channels / Q000502:physiology*; D014981:Xenopus
D015221:Potassium Channels