Posts Tagged ‘photoisomerization reaction’

Light dependent bioenergy

Larry H. Bernstein, MD, FCAP, Curator



Researchers Snapshot Bacterial Sensor’s Response to Light   5/06/2016

This illustration depicts an experiment at SLAC that revealed how a protein from photosynthetic bacteria changes shape in response to light in less than a trillionth of a second. (Credit: SLAC National Accelerator Laboratory)
This illustration depicts an experiment at SLAC that revealed how a protein from photosynthetic bacteria changes shape in response to light in less than a trillionth of a second. (Credit: SLAC National Accelerator Laboratory)

For the variety of Earth’s fauna and flora, sunlight provides nutrients essential for life.

“Converting light from the sun into energy is what keeps us alive,” Sébastien Boutet, a senior staff scientist at SLAC National Accelerator Laboratory’s Linac Coherent Light Source (LCLS), toldR&D Magazine.

While scientists know biomolecules harness light to carry out important biological processes, it’s difficult to capture these reactions on the atomic and molecular levels because they occur so quickly.

Boutet, along with a team of international researchers, used the LCLS’ powerful x-ray laser to capture such a reaction at speeds hitherto unattainable.

“We’re trying to see ultrafast reactions” and “the x-ray source that we have here is very unique,” said Boutet, who took a job at LCLS about nine years ago to develop the beam line used in the experiment.

In their study, which was published recently in Science, the team zeroed in on a light-sensitive part of a protein called photoactive yellow protein (PYP). According to SLAC, it functions as a proverbial eye in purple bacteria, allowing the organism to detect blue light and stay away from potentially harmful light.

According to Marius Schmidt, the study’s principal investigator from the University of Wisconsin, Milwaukee, the team is the first to capture real-time snapshots of an ultrafast structure transition, during which a “molecule excited by light relaxed by rearranging its structure in what is known as trans-to-cisisomerization.”

Previously, researchers had studied this PYP at atomic motions as fast as 10 billionths of a second. But with a few tweaks, they were able to glimpse the reaction 1,000 times faster than before.

It was known what was happening at the nanosecond timescale, said Boutet. But now, there’s a window into in the picosecond and sub-picosecond timescale.

During the experiment, the researchers sent a stream of PYP crystals inside a sample chamber, according to SLAC. Then, Boutet explained, they shot the crystals with laser light to start a reaction, then used an x-ray beam to see the reaction.

“Since LCLS’s x-ray pulses are extremely short, lasting only a few quadrillionths of a second, they can in principle probe processes on that very timescale … if the optical laser also matches the tremendous speed,” according to SLAC.

“These types of tools are the way to understand at the atomic and molecular level these reactions that are really essential to life,” said Boutet. “Photosynthesis is the poster child for this. If we could understand this better, we could potentially build better artificial energy conversion using the sun.”

Additionally, this technology could reveal how the human eye’s visual pigments respond to light, helping researchers understand just how excessive absorption damages the human eye.

“The techniques that we use to understand energy conversion is one of the things that LCLS is very useful for,” Boutet concluded.


Femtosecond structural dynamics drives the trans/cis isomerization in photoactive yellow protein

Visualizing a response to light

Many biological processes depend on detecting and responding to light. The response is often mediated by a structural change in a protein that begins when absorption of a photon causes isomerization of a chromophore bound to the protein. Pande et al. used x-ray pulses emitted by a free electron laser source to conduct time-resolved serial femtosecond crystallography in the time range of 100 fs to 3 ms. This allowed for the real-time tracking of the trans-cis isomerization of the chromophore in photoactive yellow protein and the associated structural changes in the protein.

Science, this issue p. 725

A variety of organisms have evolved mechanisms to detect and respond to light, in which the response is mediated by protein structural changes after photon absorption. The initial step is often the photoisomerization of a conjugated chromophore. Isomerization occurs on ultrafast time scales and is substantially influenced by the chromophore environment. Here we identify structural changes associated with the earliest steps in the trans-to-cis isomerization of the chromophore in photoactive yellow protein. Femtosecond hard x-ray pulses emitted by the Linac Coherent Light Source were used to conduct time-resolved serial femtosecond crystallography on photoactive yellow protein microcrystals over a time range from 100 femtoseconds to 3 picoseconds to determine the structural dynamics of the photoisomerization reaction.



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