Tag: Vitamin B12

Filming a vitamin B12 photoreceptor in action

Filming a vitamin B12 photoreceptor in action

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

ESRF X-rays capture vitamin B12 sensing light

ESRF X-rays capture vitamin B12 sensing light

Scientists led by the Institut de Biologie Structurale have combined advanced X-ray methods to unveil how a photoreceptor regulates carotenoid production in bacteria, including experiments at the ESRF. The results are out in Nature.

CarH is a photoreceptor which senses light through a vitamin B12 derivative and regulates carotenoid expression through direct interaction with genes. Bacteria use this remarkable machinery to regulate gene expression and produce carotenoid to protect themselves from photo-damage upon sun exposure. What scientists had never seen before was how tiny photoinduced changes at the vitamin B12 level, propagate into large-scale structural changes triggering a biological response. Now, an international collaboration has managed to film this process in unprecedented detail, with key experiments carried out at the ESRF and at XFELs.

CarH’s role has been clear since around 2015. In the dark, the protein binds to DNA and blocks the production of carotenoids. When light is present, CarH releases the DNA, allowing the cell to produce carotenoids that help defend against light-induced damage.

Previous crystal structures revealed the start and end points of this process. But the crucial missing piece was the journey in between — from the short-lived structural changes that occur immediately after light hits the vitamin B12 molecule to the large-scale conformational changes involving the whole protein structure and its interaction with DNA.

Read more on the ESRF website

Image credit: CEA and Maria Davila Miliani

New technique reveals insights on Vitamin B12

New technique reveals insights on Vitamin B12

Researchers have implemented a new technique, based on the European XFEL’s ultrashort pulses, to gain insights into two compounds featuring vitamin B12. B12 is an important compound in many biological systems, and the new method will allow scientists to develop a much deeper understanding of its structure and behavior. The technique will enable better insights for a host of biological molecules, and could help in designing targeted drug therapies.

Scientists used the European XFEL’s bright and ultrashort X-ray pulses to probe the evolution of two B12 compounds in time, at intervals of just 10 trillionths of a second (100 fs). Scientists used green light to illuminate the B12 compounds, and looked at them using a new method of X-ray spectroscopy called time-resolved Valence-to-Core X-ray Emission Spectroscopy (tr-VtC XES) to take snapshots of each molecule focusing on different aspects of their structure. Through the combination of optical and X-ray measurements, researchers were able to learn about the specific behaviors of these B12 compounds, such as their reactions to visible light, as well as the way the molecules vibrate and recover their initial configuration.

“Similar techniques have been used to investigate B12 using only visible and ultraviolet light,” says Frederico Lima, Instrument Scientist at the FXE instrument. “But the advantage of using tr-VtC XES is that you can get an element sensitive measurement that is also rather straightforward to predict using modern quantum chemical theory. In other words, it becomes easier to understand what each individual element in the molecule is doing. This gives us a more precise picture of the vitamin’s behavior than previously possible.”

The study, published in the Journal of the American Chemical Society, also addresses a problem with measuring tr-VtC XES on biological systems such as those containing B12, namely, that they produce small, difficult to detect signals.

Read more on the European XFEL website

Image: Visualisations of the structure of two vitamin B12 compounds at a 2.6 angstrom resolution, (a) in reaction with a biological structure and (b) in a water-based environment.