Which structural features of K+ channels account for: a) ion selectivity, b) voltage sensitivity, and c) ion conductance?View keyboard shortcutsEditViewInsertFormatToolsTable12ptParagraph
Question
Which structural features of K+ channels account for: a) ion selectivity, b) voltage sensitivity, and c) ion conductance?View keyboard shortcutsEditViewInsertFormatToolsTable12ptParagraph
Solution
a) Ion Selectivity: The selectivity filter is the structural feature of K+ channels that accounts for ion selectivity. This filter is located at the narrowest part of the pore and is composed of the backbone carbonyl oxygens from the K+ channel protein. The selectivity filter is precisely sized to dehydrate and accept K+ ions, but not smaller Na+ ions, thus allowing only K+ ions to pass through.
b) Voltage Sensitivity: The voltage-sensing domain (VSD) is responsible for the voltage sensitivity of K+ channels. This domain is composed of four transmembrane segments (S1-S4). The S4 segment contains positively charged residues that respond to changes in membrane potential, causing a conformational change in the channel that opens or closes the pore.
c) Ion Conductance: The pore domain, specifically the inner pore or cavity, is responsible for ion conductance in K+ channels. This domain is formed by the S5 and S6 segments and the loop connecting them. The size and properties of the inner pore determine the rate at which ions can flow through the channel, i.e., the ion conductance. The inner pore can be opened or closed by conformational changes in the protein, which are controlled by the voltage-sensing domain.
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