How Does Vision Work?

In a breakthrough study conducted at Cornell University, a team of researchers has exposed the molecular basis of vision and unlocked new insight into how the eyes, one of the most complex organs created by the human body, operate.

Using cryo-electron microscopy, the researchers were able to map atomic-resolution structures of the rhodopsin-transducin complex. This offered a new understanding of the three-dimensional structure of the protein complex, which plays a central role in the vertebrate visual system that allows the human eye to amplify signals from photon light particles and generate vision.

Vision: 101

Made up of three complex layers, vertebrate eyes convert light signals into images that are deciphered by the brain. The process starts when light waves pass through the outer lens, where it's focused to form an image. The information is then sent to the retina, where photoreceptors interpret the data and convert it to electrical impulses. These are then sent to the brain, which uses the electrical impulses to construct images.

The pivotal role of G-protein-coupled receptors

For the Cornell University study, the researchers were especially interested in G-protein-coupled receptors (GPCRs), a diverse group of membrane receptors that receive messages in the form of light energy, as well as proteins, peptides, sugars and lipids. GPCRs are involved in almost all biological processes that take place in the human body, including light perception.

In vertebrate vision, G-protein-coupled receptors are equipped with a light-sensitive receptor protein called rhodopsin. These ultra-sensitive biological pigments can detect signals from a single photon and amplify the date by 100,000 times. Using advanced cryo-electron microscopy technology, the team were able to create atomic-resolution structures of the rhodopsin-transducin complex and reveal new insight into the molecular mechanics of vertebrate vision, as well as how GPCRs influence other biological processes.

Researchers aim to develop GPCR specific drugs

The human body is influenced by more than 800 GPCRs, which dictate functions such as taste, smell, muscle contraction and heart regulation. This makes GPCRs targets for more than 30% of commercially sold drugs. The team hope that the new information relating to how receptors pair with different G proteins can be used to develop drugs that regulate GPCR signalling and minimise side effects.  

"What we've learnt from these structures at an atomic level may be broadly applicable to other GPCR signalling systems," explains Sekar Ramachandran, co-first author of the study and senior research associate at Cornell University.

"A lot of drug side effects occur when therapies are not specific enough and target both harmful and beneficial pathways," adds Yang Gao, co-first author of the paper and postdoctoral researcher.

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