The big bang of the vision finally unveiled. Swiss researchers have managed to visualize the dynamics of the very first moments of the visual process, a molecular dance that lasts only a few thousandths of a billionth of a second (picoseconds). This technical feat, described in the review Nature from 22 marswas made by shining a giant “telescope” on tiny molecular crystals.
This fascinating ballet begins when a photon strikes the retina. Or, more precisely, when it hits a protein called “rhodopsin”, the visual pigment that equips cells called “rods”. It is one of the two types of photoreceptor cells in the retina, responsible for capturing light signals and then converting them into an electrical signal. Once processed by the retina, this nerve impulse will be sent by the optic nerve to the visual areas of the brain, which will process it to produce a mental image.
The molecule of rhodopsin, or “retinal purple”, is a baroque building. It has seven helices that cross the cell membrane. But, above all, it houses the key to the system: retinal, a derivative of vitamin A, nestled in the heart of these seven helices. This very small molecule, sensitive to light, will act as a visual switch.
From picoseconds to femtoseconds
When rhodopsin is exposed to light, this retinal absorbs a photon and uses the energy thus received to spread out in space. It then changes from a bent form (11-cis isomer) to a stretched form (all-trans isomer). This has been known for a long time. However, ” despite decades of attempts, no one had observed this reaction in real time [le déploiement du rétinal dans l’espace] »note Marius Schmidt, of the University of Wisconsin, and Emina Stojkovic, of the University of Illinois, in the United States, who did not participate in the study.
To achieve this feat, the doctoral student who co-authored this work, Thomas Gruhl, worked for months on this question: how to produce rhodopsin microcrystals from cow retina? This puzzle solved, these microcrystals were sifted through state-of-the-art equipment: a latest-generation free-electron and X-ray laser (XFEL), installed in northern Switzerland (canton of Aargau). This Swiss facility is not the most powerful laser of this type in the world, but it is already powerful enough to monitor ultrafast phenomena, such as the appearance of new molecules during chemical reactions. Its principle: electrons pass through a linear accelerator, then through “magnetic undulators” which give them a sinuous trajectory. They then emit intense and ultra-short X-ray pulses: from 1 to 60 femtoseconds, or from 1 to 60 millionths of a billionth of a second!
You have 42.31% of this article left to read. The following is for subscribers only.
