Roller A, Natura G, Bihler H, Slayman C L, Eing C, Bertl A
Botanisches Institut I, Universität Karlsruhe, Kaiserstrasse 12, 76128 Karlsruhe, Germany.
Pflugers Arch. 2005 Nov;451(2):362-70. doi: 10.1007/s00424-005-1418-2. Epub 2005 Aug 27.
The yeast plasma-membrane potassium channel, Tok1p, is a voltage-dependent outward rectifier, the gating and steady-state conductance of which are conspicuously modulated by extracellular [K(+)] (K(+)). Activation is slow at high K(+), showing time constants (tau(a)) of approximately 90 ms when K(+) is 150 mM (depolarizing step to +100 mV), and inactivation is weak (<30%) during sustained depolarization. Lowering K(+) accelerates activation, increases peak current, and enhances inactivation, so that at 15 mM K(+) tau(a) is less than 50 ms and inactivation suppresses approximately 60% of peak current. Two negative residues, Asp292 and Asp426, near the mouth of the assembled channel, modulate both kinetics and conductance of the channel. Charge neutralization in the mutant Asp292Asn allows fast activation (tau(a) approximately 20 ms) at high K(+), peak currents diminishing with decreasing K(+), and fast, nearly complete, inactivation. The voltage dependence of tau(a) persists in the mutant, but the K(+) dependence almost disappears. Similar but smaller changes are seen in the Asp426Asn mutant, implying that pore geometry in the functional channel has twofold, not fourfold, symmetry.
酵母质膜钾通道Tok1p是一种电压依赖性外向整流器，其门控和稳态电导受到细胞外[K⁺]（[K⁺]ₒ）的显著调节。在高[K⁺]ₒ时激活缓慢，当[K⁺]ₒ为150 mM（去极化至+100 mV）时，时间常数（τₐ）约为90 ms，并且在持续去极化期间失活较弱（<30%）。降低[K⁺]ₒ会加速激活、增加峰值电流并增强失活，因此在15 mM [K⁺]ₒ时，τₐ小于50 ms，失活可抑制约60%的峰值电流。在组装通道口附近的两个负性残基Asp292和Asp426调节通道的动力学和电导。突变体Asp292Asn中的电荷中和允许在高[K⁺]ₒ时快速激活（τₐ约为20 ms），峰值电流随[K⁺]ₒ降低而减小，并且快速、几乎完全失活。τₐ的电压依赖性在突变体中持续存在，但[K⁺]ₒ依赖性几乎消失。在Asp426Asn突变体中观察到类似但较小的变化，这意味着功能性通道中的孔几何结构具有双重对称性，而非四重对称性。
