Ottschytsch Natacha, Raes Adam L, Timmermans Jean-Pierre, Snyders Dirk J
Laboratory for Molecular Biophysics, Physiology and Pharmacology, Department of Biomedical Sciences, University of Antwerp (CDE), Universiteitsplein 1, T4.21, 2610 Antwerp, Belgium.
J Physiol. 2005 Nov 1;568(Pt 3):737-47. doi: 10.1113/jphysiol.2005.090142. Epub 2005 Aug 11.
The subunit Kv6.3 encodes a voltage-gated potassium channel belonging to the group of electrically silent Kv subunits, i.e. subunits that do not form functional homotetrameric channels. The lack of current, caused by retention in the endoplasmic reticulum (ER), was overcome by coexpression with Kv2.1. To investigate whether a specific section of Kv6.3 was responsible for ER retention, we constructed chimeric subunits between Kv6.3 and Kv2.1, and analysed their subcellular localization and functionality. The results demonstrate that the ER retention of Kv6.3 is not caused by the N-terminal A and B box (NAB) domain nor the intracellular N- or C-termini, but rather by the S1-S6 core protein. Introduction of individual transmembrane segments of Kv6.3 in Kv2.1 was tolerated, with the exception of S6. Indeed, introduction of the S6 domain of Kv6.3 in Kv2.1 was enough to cause ER retention, which was due to the C-terminal section of S6. The S4 segment of Kv6.3 could act as a voltage sensor in the Kv2.1 context, albeit with a major hyperpolarizing shift in the voltage dependence of activation and inactivation, apparently caused by the presence of a tyrosine in Kv6.3 instead of a conserved arginine. This study suggests that the silent behaviour of Kv6.3 is largely caused by the C-terminal part of its sixth transmembrane domain that causes ER retention of the subunit.
亚基Kv6.3编码一种电压门控钾通道，属于电沉默Kv亚基组，即不形成功能性同四聚体通道的亚基。由内质网（ER）滞留引起的电流缺失，通过与Kv2.1共表达得以克服。为了研究Kv6.3的特定区域是否负责ER滞留，我们构建了Kv6.3和Kv2.1之间的嵌合亚基，并分析了它们的亚细胞定位和功能。结果表明，Kv6.3的ER滞留不是由N端A和B框（NAB）结构域、细胞内N端或C端引起的，而是由S1-S6核心蛋白引起的。除了S6之外，Kv6.3的单个跨膜片段引入Kv2.1中是可以耐受的。事实上，将Kv6.3的S6结构域引入Kv2.1中足以导致ER滞留，这是由于S6的C端部分。Kv6.3的S4片段在Kv2.1环境中可以作为电压传感器，尽管在激活和失活的电压依赖性上有一个主要的超极化偏移，这显然是由Kv6.3中存在酪氨酸而不是保守的精氨酸引起的。这项研究表明，Kv6.3的沉默行为很大程度上是由其第六个跨膜结构域的C端部分引起的，该部分导致亚基滞留在内质网中。
