Scientists from the Paul Scherrer Institute (PSI) have published a study in the journal Nature Structural & Molecular Biology. By studying bovine eyes via cryo-electron microscopy and encoding the three-dimensional structure of the cyclic nucleotide-gated (CNG) ion channel, they gained further insight into how vision works. This ion channel is a protein located in the cell membrane of retinal rod cells, which is involved in the sight of dim light, conveying optical information from the eye to the brain. The CNG ion channel acts as a gatekeeper at the cellular membrane, controlling the passage of particles to the inside of the rod cell. It is important to note that this channel is entirely open in the darkness. However, when light is captured by the eye, a cascade of events is triggered in the rod cells, leading to the gate’s closure, thus inhibiting the entrance of particles. A visual picture is formed when the electrochemical signal travels via the nerve cells to the visual cortex in the brain.
This is a significant finding because if a genetic disorder disrupts how these channels work, the person will go blind. Further knowledge about the function and structure of this protein sheds more light on the underlying mechanism of vision and potential novel treatments for conditions that may arise, such as retinitis pigmentosa. A possible reason for this condition, which is caused by the eventual death of the photoreceptors, might be due to the inability to produce the CNG ion channel correctly. Because of genetic defects, the channel does not entirely close when light reaches the eye, disrupting the cell’s electrochemical balance and eventually leading to cell death.
The CNG ion channel itself has 4 parts: 3 subunits A and 1 subunit B. An interesting fact from this study is that a single amino acid in the B subunit protrudes from the CNG channel, acting as a barrier, narrowing the gateway so no particles are able to get through. Such narrow spaces were known in the A subunits but not in the B. This study also states that it is important to note that all living creatures with this ion channel present this same protruding amino acid at this position. The fact that it has been preserved throughout evolution shows that it must be essential for the proper functioning of the channel.
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