TY - JOUR
T1 - Ion-binding properties of a K+ channel selectivity filter in different conformations
AU - Liu, Shian
AU - Focke, Paul J.
AU - Matulef, Kimberly
AU - Bian, Xuelin
AU - Moënne-Loccoz, Pierre
AU - Valiyaveetil, Francis I.
AU - Lockless, Steve W.
PY - 2015/12/8
Y1 - 2015/12/8
N2 - K+ channels are membrane proteins that selectively conduct K+ ions across lipid bilayers. Many voltage-gated K+ (KV) channels contain two gates, one at the bundle crossing on the intracellular side of the membrane and another in the selectivity filter. The gate at the bundle crossing is responsible for channel opening in response to a voltage stimulus, whereas the gate at the selectivity filter is responsible for C-type inactivation. Together, these regions determine when the channel conducts ions. The K+ channel from Streptomyces lividians (KcsA) undergoes an inactivation process that is functionally similar to KV channels, which has led to its use as a practical system to study inactivation. Crystal structures of KcsA channels with an open intracellular gate revealed a selectivity filter in a constricted conformation similar to the structure observed in closed KcsA containing only Na+ or low [K+]. However, recent work using a semisynthetic channel that is unable to adopt a constricted filter but inactivates like WT channels challenges this idea. In this study, we measured the equilibrium ion-binding properties of channels with conductive, inactivated, and constricted filters using isothermal titration calorimetry (ITC). EPR spectroscopy was used to determine the state of the intracellular gate of the channel, which we found can depend on the presence or absence of a lipid bilayer. Overall, we discovered that K+ ion binding to channels with an inactivated or conductive selectivity filter is different from K+ ion binding to channels with a constricted filter, suggesting that the structures of these channels are different.
AB - K+ channels are membrane proteins that selectively conduct K+ ions across lipid bilayers. Many voltage-gated K+ (KV) channels contain two gates, one at the bundle crossing on the intracellular side of the membrane and another in the selectivity filter. The gate at the bundle crossing is responsible for channel opening in response to a voltage stimulus, whereas the gate at the selectivity filter is responsible for C-type inactivation. Together, these regions determine when the channel conducts ions. The K+ channel from Streptomyces lividians (KcsA) undergoes an inactivation process that is functionally similar to KV channels, which has led to its use as a practical system to study inactivation. Crystal structures of KcsA channels with an open intracellular gate revealed a selectivity filter in a constricted conformation similar to the structure observed in closed KcsA containing only Na+ or low [K+]. However, recent work using a semisynthetic channel that is unable to adopt a constricted filter but inactivates like WT channels challenges this idea. In this study, we measured the equilibrium ion-binding properties of channels with conductive, inactivated, and constricted filters using isothermal titration calorimetry (ITC). EPR spectroscopy was used to determine the state of the intracellular gate of the channel, which we found can depend on the presence or absence of a lipid bilayer. Overall, we discovered that K+ ion binding to channels with an inactivated or conductive selectivity filter is different from K+ ion binding to channels with a constricted filter, suggesting that the structures of these channels are different.
KW - Electron paramagnetic resonance spectroscopy
KW - Inactivation
KW - Ion binding
KW - Isothermal titration calorimetry
KW - K channel
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U2 - 10.1073/pnas.1510526112
DO - 10.1073/pnas.1510526112
M3 - Article
C2 - 26598654
AN - SCOPUS:84949309776
SN - 0027-8424
VL - 112
SP - 15096
EP - 15100
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 49
ER -