Ashmole I, Goodwin P A, Stanfield P R
Department of Cell Physiology and Pharmacology, University of Leicester, UK.
Pflugers Arch. 2001 Sep;442(6):828-33. doi: 10.1007/s004240100620.
We have cloned a novel member of the tandem pore K+ channel family from human brain cDNA. The novel cDNA encodes a 330-residue polypeptide of predicted molecular mass 36 kDa. We have named the channel TASK-5 owing to its sequence homology with TASK-1 and TASK-3. TASK-5 mRNA is expressed in pancreas, liver, kidney, lung, ovary, testis and heart. However, expression of TASK-5 in heterologous systems failed to elicit ionic currents. Removal of a putative endoplasmic reticulum retention sequence did not alter this finding and the distribution of channel proteins in HEK293 cells was similar for both TASK-1 and TASK-5. We tested whether TASK-5 could form heteromers with TASK-1. We show a mutant form of TASK-1 (H98N) to have a radically reduced sensitivity to acidification. Proton sensitivity could be rescued by injecting equimolar amounts of wild-type and mutant TASK-1 cRNA into Xenopus oocytes; the effect was that expected if half the channels formed are heteromers. Co-expression of TASK-5 with TASK-1 H98N does not affect the proton sensitivity of mutant TASK-1; thus TASK-5 appears not to form heteromers with TASK-1. Nonetheless, TASK-5 may require some other, unidentified partner subunit to form functional channels in the plasma membrane or it may form a channel in an intracellular organelle.
我们从人脑海马体cDNA中克隆出了串联孔道K⁺通道家族的一个新成员。这个新的cDNA编码一个由330个氨基酸残基组成的多肽，预测分子量为36 kDa。由于其与TASK-1和TASK-3的序列同源性，我们将该通道命名为TASK-5。TASK-5 mRNA在胰腺、肝脏、肾脏、肺、卵巢、睾丸和心脏中均有表达。然而，在异源系统中表达TASK-5未能引发离子电流。去除一个假定的内质网保留序列并没有改变这一结果，并且TASK-1和TASK-5在HEK293细胞中的通道蛋白分布相似。我们测试了TASK-5是否能与TASK-1形成异源二聚体。我们发现TASK-1的一种突变形式（H98N）对酸化的敏感性大幅降低。通过向非洲爪蟾卵母细胞中注射等摩尔量的野生型和突变型TASK-1 cRNA，可以恢复质子敏感性；如果形成的通道中有一半是异源二聚体，那么预期会出现这种效果。TASK-5与TASK-1 H98N共表达并不影响突变型TASK-1的质子敏感性；因此，TASK-5似乎不会与TASK-1形成异源二聚体。尽管如此，TASK-5可能需要一些其他未鉴定的伴侣亚基才能在质膜中形成功能性通道，或者它可能在细胞内细胞器中形成通道。
