Using X-ray free-electron lasers and synchrotron light at facilities in Switzerland, Japan, France and the UK, a worldwide collaboration of scientists have discovered how a vitamin B12-based photoreceptor works. Understanding how photoreceptors function aids future technological applications, such as optogenetics, that involve controlling cellular processes with light. The findings are published in Nature.
Vitamin B12 is an organometallic cofactor found in many enzymes that control essential processes in various organisms, including humans. It came as a surprise a decade ago that vitamin B12 derivatives had been repurposed for light sensing by a large family of previously unknown photoreceptors in bacteria that fulfil various functions.
The prototypical B12 photoreceptor CarH, for example, regulates the expression of genes involved in protecting bacteria against excess sunlight. It achieves this by binding to DNA in the dark, acting as a molecular doorstop. Upon illumination, its tetrameric architecture breaks apart, enabling transcription by unbinding from DNA.
The way in which this and other B12 photoreceptors function at a molecular level has remained a mystery ever since. However, an international consortium led by scientists at the Institut de Biologie Structurale in Grenoble, France has now combined experimental techniques using X-ray free-electron lasers at the Paul Scherrer Institute PSI in Switzerland (SwissFEL) and Japan (SACLA), as well as the synchrotrons in France (ESRF) and the UK (Diamond Light Source), with quantum-chemical calculations to uncover the inner workings of CarH.
Read more on the PSI website
Image: John Beale is responsible for macromolecular crystallography at the Cristallina experimental station of SwissFEL
Credit: © Paul Scherrer Institute PSI / Markus Fische
