Tuning magnesium sensitivity of BK channels by mutations.
Intracellular Mg(2+) at physiological concentrations activates mSlo1 BK channels by binding to a metal-binding site in the cytosolic domain. Previous studies suggest that residues E374, Q397, and E399 are important in Mg(2+) binding. In the present study, we show that mutations of E374 or E399 to other amino acids, except for Asp, abolish Mg(2+) sensitivity. These results further support that the side chains of E374 and E399 are essential for Mg(2+) coordination. To the contrary, none of the Q397 mutations abolishes Mg(2+) sensitivity, suggesting that its side chain may not coordinate to Mg(2+). However, because Q397 is spatially close to E374 and E399, its mutations affect the Mg(2+) sensitivity of channel gating by either reducing or increasing the Mg(2+) binding affinity. The pattern of mutational effects and the effect of chemical modification of Q397C indicate that Q397 is involved in the Mg(2+)-dependent activation of BK channels and that mutations of Q397 alter Mg(2+) sensitivity by affecting the conformation of the Mg(2+) binding site as well as by electrostatic interactions with the bound Mg(2+) ion.
Yang
Huanghe
H
Department of Biomedical Engineering and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, Missouri 63130, USA.
Hu
Lei
L
Shi
Jingyi
J
Cui
Jianmin
J
D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D002413:Cations, Divalent; D005260:Female; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000235:genetics / Q000502:physiology*; D008274:Magnesium / Q000378:metabolism*; D051379:Mice; D009865:Oocytes / Q000502:physiology; D055672:Static Electricity; D014982:Xenopus laevis
D002413:Cations, Divalent; C465449:Kcnma1 protein, mouse; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D008274:Magnesium