The CNG channel has a 'hanging-gondola' architecture
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Figure 4. Surface representations of the CNG channel at a contour level that includes the mass of four subunits. (A-E) show five different views of the molecule. We propose that A is viewed from the cytosolic side of the membrane while B is viewed from the extracellular side. C, D and E are viewed from a direction parallel to the membrane and E shows the putative position of the lipid bilayer, represented by two lines separated by 40Å. F-I show sections through the electron density along the lines indicated on D. The scale bars are 50Å in length. |
| Many of the ion channels of the nervous system have an architecture that, in the case of the Shaker potassium channel, has been described as a 'hanging gondola' (Sokolova et al., 2001). This describes an arrangement of cytoplasmic domains that 'hang' underneath the transmembrane part of the channel without forming part of the channel pore. Such an arrangement has been observed in the acetylcholine receptor, (Miyazawa et al., 1999) where narrow transverse openings in the cytoplasmic parts of the channel may serve as filters to limit access to the channel pore. The structure of the voltage-gated potassium channel (Sokolova et al., 2001) also shows a domain 'hanging' under the pore forming part of the channel. In this case, the hanging structure is formed from the tetramerization domains of the channel. This 'T1 domain' plays a role in determining which potassium channel subunits interact together in functional complexes (Li et al., 1992) and provides a docking site for the b-subunits that modulate the channel gating properties (Rettig et al., 1994, Gulbis et al., 2000). In the case of the cyclic nucleotide-gated channel, we propose the 'hanging goldola' to contain the ligand-binding domains. |
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