Henn D K, Baumann A, Kaupp U B
Institut für Biologische Informationsverarbeitung, Forschungszentrum Jülich, Germany.
Proc Natl Acad Sci U S A. 1995 Aug 1;92(16):7425-9. doi: 10.1073/pnas.92.16.7425.
Cyclic nucleotide-gated (CNG) cation channels contain two short sequence motifs--a residual voltage-sensor (S4) and a pore-forming (P) segment--that are reminiscent of similar segments in voltage-activated Shaker-type K+ channels. It has been tacitly assumed that CNG channels and this K+ channel subfamily share a common overall topology, characterized by a hydrophobic domain comprising six membrane-spanning segments. We have systematically investigated the topology of CNG channels from bovine rod photoreceptor and Drosophila melanogaster by a gene fusion approach using the bacterial reporter enzymes alkaline phosphatase and beta-galactosidase, which are active only in the periplasm and only in the cytoplasm, respectively. Enzymatic activity was determined after expression of fusion constructs in Escherichia coli. CNG channels were found to have six membrane-spanning segments, suggesting that CNG and Shaker-type K+ channels, albeit distant relatives within a gene superfamily of ion channels, share a common topology.
环核苷酸门控（CNG）阳离子通道包含两个短序列基序——一个残余电压感受器（S4）和一个成孔（P）片段——这让人联想到电压激活的Shaker型钾通道中的类似片段。一直以来都默认认为CNG通道和这个钾通道亚家族具有共同的整体拓扑结构，其特征是由六个跨膜片段组成的疏水结构域。我们通过基因融合方法，利用仅在周质和仅在细胞质中具有活性的细菌报告酶碱性磷酸酶和β-半乳糖苷酶，系统地研究了来自牛视杆光感受器和黑腹果蝇的CNG通道的拓扑结构。在大肠杆菌中表达融合构建体后测定酶活性。发现CNG通道有六个跨膜片段，这表明CNG通道和Shaker型钾通道尽管是离子通道基因超家族中的远亲，但具有共同的拓扑结构。
