Morales M J, Wee J O, Wang S, Strauss H C, Rasmusson R L
Department of Pharmacology, Duke University Medical Center, Durham, NC 27710, USA.
Proc Natl Acad Sci U S A. 1996 Dec 24;93(26):15119-23. doi: 10.1073/pnas.93.26.15119.
Voltage-gated K+ channels are complexes of membrane-bound, ion-conducting alpha and cytoplasmic ancillary (beta) subunits. The primary physiologic effect of coexpression of alpha and beta subunits is to increase the intrinsic rate of inactivation of the alpha subunit. For one beta subunit, Kv beta 1.1, inactivation is enhanced through an N-type mechanism. A second beta subunit, Kv beta 1.2, has been shown to increase inactivation, but through a distinct mechanism. Here we show that the degree of enhancement of Kv beta 1.2 inactivation is dependent on the amino acid composition in the pore mouth of the alpha subunit and the concentration of extracellular K+. Experimental conditions that promote C-type inactivation also enhance the stimulation of inactivation by Kv beta 1.2, showing that this beta subunit directly stimulates C-type inactivation. Chimeric constructs containing just the nonconserved N-terminal region of Kv beta 1.2 fused with an alpha subunit behave in a similar fashion to coexpressed Kv beta 1.2 and alpha subunit. This shows that it is the N-terminal domain of Kv beta 1.2 that mediates the increase in C-type inactivation from the cytoplasmic side of the pore. We propose a model whereby the N terminus of Kv beta 1.2 acts as a weakly binding "ball" domain that associates with the intracellular vestibule of the alpha subunit to effect a conformational change leading to enhancement of C-type inactivation.
电压门控钾离子通道是由膜结合的离子传导α亚基和胞质辅助（β）亚基组成的复合物。α亚基和β亚基共表达的主要生理效应是增加α亚基的内在失活速率。对于一个β亚基Kvβ1.1，失活通过N型机制增强。第二个β亚基Kvβ1.2已被证明可增加失活，但通过不同的机制。在这里我们表明，Kvβ1.2失活增强的程度取决于α亚基孔口的氨基酸组成和细胞外钾离子的浓度。促进C型失活的实验条件也增强了Kvβ1.2对失活的刺激作用，表明该β亚基直接刺激C型失活。仅包含与α亚基融合的Kvβ1.2非保守N端区域的嵌合构建体的行为与共表达的Kvβ1.2和α亚基相似。这表明是Kvβ1.2的N端结构域从孔的胞质侧介导了C型失活的增加。我们提出了一个模型，其中Kvβ1.2的N端充当弱结合的“球”结构域，与α亚基的细胞内前庭结合，从而引起构象变化，导致C型失活增强。
