N type rapid inactivation in human Kv1.4 channels: functional role of a putative C-terminal helix.
Voltage gated potassium channels are tetrameric membrane proteins, which have a central role in cellular excitability. Human Kv1.4 channels open on membrane depolarization and inactivate rapidly by a 'ball and chain' mechanism whose molecular determinants have been mapped to the cytoplasmic N terminus of the channel. Here we show that the other terminal end of the channel also plays a role in channel inactivation. Swapping the C-terminal residues of hKv1.4 with those from two non-inactivating channels (hKv1.1 and hKv1.2) affects the rates of inactivation, as well as the recovery of the channel from the inactivated state. Secondary structure predictions of the hKv1.4 sequence reveal a helical structure at its distal C-terminal. Complete removal or partial disruption of this helical region results in channels with remarkably slowed inactivation kinetics. The ionic selectivity and voltage-dependence of channel opening were similar to hKv1.4, indicative of an unperturbed channel pore. These results demonstrate that fast inactivation is modulated by structural elements in the C-terminus, suggesting that the process involves the concerted action of the N- and C-termini.
Sankaranarayanan
Kavitha
K
National Centre for Biological Sciences, Bangalore, India.
Varshney
Anurag
A
Mathew
M K
MK
D000595:Amino Acid Sequence; D000818:Animals; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D007700:Kinetics; D051665:Kv1.4 Potassium Channel / Q000737:chemistry* / Q000378:metabolism; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry; D016415:Sequence Alignment; D019789:Tetraethylammonium / Q000494:pharmacology; D014982:Xenopus laevis
C496977:KCNA4 protein, human; D051665:Kv1.4 Potassium Channel; D021122:Protein Subunits; D019789:Tetraethylammonium; D011188:Potassium