Shifting the Gating Equilibrium of a Potassium Channel via Hydrophobic Mismatch

Abstract

When the potassium channel KcsA transitions from the closed to the open state, the inner helices transition outward and away from the axis of symmetry. This substantial conformational change can be expected to significantly alter the both the shape and volume of the protein within the membrane. In this study we explored the possibility of exploiting this shape and volume change to gate the channel using hydrophobic mismatch to alter the membrane induced lateral forces on the channel. We spin-labeled residues of the inner helices known to exhibit strong spin-spin interaction (residues 103, 108, 109, 112, 116 and 118) and monitored spin-spin interactions by cw-EPR as we altered both pH and membrane composition. As previously observed, the spin-spin interactions weakened when the open state was favored by lowering pH, due to the outward movement of the inner helices. We then altered the length of the acyl chains from 18 to 22 carbons at neutral pH. Over this range of chain lengths the strength of the spin-spin interactions changed to approximately the same degree as observed when lowering pH. We interpret these results to mean that the state distribution of the KcsA channel can be shifted by altering the membrane induced lateral forces on the channel.