Open and Closed Conformations
Attempts continue to relate the structure of the mammalian voltage-gated K+ channel to its ability to respond to the voltage that exists across the membrane. Specific domains of the channel subunits have been identified that are important for voltage-sensing and converting between the open conformation of the channel and closed conformations. There are at least two closed conformations; in one, the channel can open if the membrane potential becomes positive inside. Voltage-gated K+ channels inactivate after opening, entering a distinctive, second closed conformation. In the inactivated conformation, the channel cannot open, even if the transmembrane voltage is favorable. The amino terminal domain of the K+ channel or an auxiliary protein can mediate "N-type" inactivation. The former has been described as a "ball and chain" model, where the N-terminus of the protein forms a ball that is tethered to the rest of the protein through a loop (the chain). The tethered ball is transiently sucked into the inner porehole, preventing ion movement through the channel.
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