The KcsA channel is considered a model channel because the KcsA structure provides a framework for understanding K⁺ channel conduction, which has three parts: Potassium selectivity, channel gating by pH sensitivity, and voltage-gated channel inactivation.
K⁺ ion permeation occurs at the upper selectivity filter region of the pore, while pH gating rises from the protonation of transmembrane helices at the end of the pore.
At low pH, the M2 helix is protonated, shifting the ion channel from closed to open conformation.
As ions flow through the channel, voltage gating mechanisms are thought to induce interactions between Glu71 and Asp80 in the selectivity filter, which destabilize the conductive conformation and facilitate entry into a long-lived nonconducting state that resembles the C-type–inactivation of voltage-dependent channels.

In the nonconducting conformation of KcsA at pH 7, K⁺ is bound tightly to coordinating oxygens of the selectivity filter and the four TM2 helices converge near the cytoplasmic junction to block the passage of any potassium ions.
At pH 4 however, KcsA undergoes millisecond-timescale conformational exchanges filter permeating and nonpermeating states and between the open and closed conformations of the M2 helices.
While these distinct conformational changes occur in separate regions of the channel, the molecular behavior of each region is linked by both electrostatic interactions and allostery.
The dynamics of this exchange stereochemical configurations in the filter provides the physical basis for simultaneous K⁺ conductance and gating.
The KcsA channel is considered a model channel because the KcsA structure provides a framework for understanding K⁺ channel conduction, which has three parts: Potassium selectivity, channel gating by pH sensitivity, and voltage-gated channel inactivation. K⁺ ion permeation occurs at the upper selectivity filter region of the pore, while pH gating rises from the protonation of transmembrane helices at the end of the pore. At low pH, the M2 helix is protonated, shifting the ion channel from closed to open conformation. As ions flow through the channel, voltage gating mechanisms are thought to induce interactions between Glu71 and Asp80 in the selectivity filter, which destabilize the conductive conformation and facilitate entry into a long-lived nonconducting state that resembles the C-type–inactivation of voltage-dependent channels.
In the nonconducting conformation of KcsA at pH 7, K⁺ is bound tightly to coordinating oxygens of the selectivity filter and the four TM2 helices converge near the cytoplasmic junction to block the passage of any potassium ions. At pH 4 however, KcsA undergoes millisecond-timescale conformational exchanges filter permeating and nonpermeating states and between the open and closed conformations of the M2 helices. While these distinct conformational changes occur in separate regions of the channel, the molecular behavior of each region is linked by both electrostatic interactions and allostery. The dynamics of this exchange stereochemical configurations in the filter provides the physical basis for simultaneous K⁺ conductance and gating.
KcsA potassium channel