MIT chemists have made a groundbreaking discovery about the efficiency of photosynthetic light-harvesting proteins, shedding light on the disorganized arrangement that powers their remarkable energy transduction. Contrary to previous assumptions, the disordered configuration of these proteins in light-harvesting complexes is not accidental but purposefully evolved for maximizing efficiency.
During the process of photosynthesis, cells capture sunlight, and photons of energy traverse a series of light-harvesting proteins until they reach the photosynthetic reaction center. This energy is then converted into electrons, ultimately fueling the production of essential sugar molecules.
The efficiency with which energy is transferred through the light-harvesting complex is astonishingly high, with nearly every absorbed photon generating an electron—an extraordinary phenomenon known as near-unity quantum efficiency.
In a recent study published in the Proceedings of the National Academy of Sciences, MIT chemists offer a potential explanation for the high efficiency of the light-harvesting complex. By successfully measuring the energy transfer between these proteins for the first time, the researchers discovered that the disordered arrangement plays a crucial role in boosting the efficiency of energy transduction.
Gabriela Schlau-Cohen, an associate professor of chemistry at MIT and the senior author of the study, explains, “The disordered organization of the light-harvesting proteins enhances the efficiency of that long-distance energy transduction—the key to the antenna’s functionality.”
Purple bacteria, commonly used as a model for studying photosynthetic light-harvesting, were the focus of this investigation. Within these bacteria, captured photons travel through light-harvesting complexes comprising proteins and light-absorbing pigments like chlorophyll. While scientists have previously examined how energy moves within a single protein using ultrafast spectroscopy, studying inter-protein energy transfer has proven challenging due to the need for controlled protein positioning.
To overcome this challenge, the MIT team engineered synthetic nanoscale membranes resembling natural cell membranes. These nanodiscs allowed them to measure energy transfer between two proteins embedded within the discs by precisely controlling the distance between them.
The researchers embedded two versions of the primary light-harvesting protein, LH2 and LH3, found in purple bacteria into the nanodiscs. LH2 is present under normal light conditions, while LH3 is expressed during low light conditions. Using cryo-electron microscopy, the team confirmed that the proteins were positioned similarly to those in native membranes. Moreover, they measured the distances between the light-harvesting proteins, which ranged from 2.5 to 3 nanometers.
By leveraging ultrafast spectroscopy, the researchers observed the energy transfer between closely spaced proteins, finding that it takes approximately 6 picoseconds for energy to travel between them. However, when the proteins were farther apart, the transfer time increased to around 15 picoseconds.
Faster energy transfer translates to higher efficiency, as longer journeys result in more energy loss during the process. Surprisingly, the researchers discovered that proteins arranged in a disordered structure exhibited more efficient energy transfer compared to those in an ordered lattice structure. This finding challenges the notion that ordered arrangements are more efficient and suggests that biology may have evolved to take advantage of the benefits conferred by disorder.
Having established the ability to measure inter-protein energy transfer, the MIT team plans to investigate energy transfer between other proteins, including those from the antenna to the reaction center. They also intend to explore energy transfer in antenna proteins from organisms beyond purple bacteria, such as green plants.
The research received primary funding from the U.S. Department of Energy.
Table of Contents
Frequently Asked Questions (FAQs) about photosynthetic light-harvesting efficiency
What did the MIT chemists discover about photosynthetic light-harvesting proteins?
The MIT chemists discovered that the disorganized arrangement of proteins in light-harvesting complexes enhances the efficiency of energy transfer, contrary to the assumption that ordered structures are more efficient. This suggests that the chaotic arrangement may have evolved for maximum efficiency.
How does energy transfer occur in the light-harvesting complex?
When photosynthetic cells absorb light, packets of energy called photons leap between a series of light-harvesting proteins until they reach the photosynthetic reaction center. There, the energy is converted into electrons, which power the production of sugar molecules.
What is near-unity quantum efficiency?
Near-unity quantum efficiency refers to the extraordinary phenomenon where nearly every absorbed photon of light generates an electron in the light-harvesting complex. It signifies a highly efficient energy transfer process.
How did the MIT researchers measure energy transfer between light-harvesting proteins?
The researchers designed synthetic nanoscale membranes, called nanodiscs, with embedded proteins to measure energy transfer. By controlling the distance between two proteins within the nanodiscs, they were able to observe how energy moved between them using ultrafast spectroscopy.
What did the researchers find about protein arrangement and energy transfer efficiency?
Contrary to expectations, the researchers found that proteins arranged in a disordered structure exhibited more efficient energy transfer than those in an ordered lattice structure. This suggests that nature may have evolved to take advantage of the benefits offered by disorder in optimizing energy transfer.
What are the future plans of the MIT researchers?
Having established the ability to measure inter-protein energy transfer, the researchers plan to explore energy transfer between other proteins, including those from the antenna to the reaction center. They also aim to study energy transfer in antenna proteins from organisms other than purple bacteria, such as green plants.
More about photosynthetic light-harvesting efficiency
- MIT News: Nature’s Chaos That Powers Life: MIT Chemists Discover Why Photosynthetic Light-Harvesting Is So Efficient
- Proceedings of the National Academy of Sciences: Elucidating interprotein energy transfer dynamics within the antenna network from purple bacteria
- MIT Department of Chemistry: Gabriela Schlau-Cohen’s Research Group
3 comments
wow, this is sooo cool!! MIT chemists discover dat disorganizd arrangement of proteins actually makes energy transfer more efficient! who knew?! Nature is just amazing! #photosynthetic #energytransfer
So, MIT researchers reveal dat disorganized protein arrangement actually helps photosynthetic cells! It’s like nature knows what it’s doing! Can’t wait to see more discoveries in energy transfer! #sustainability #plants
Mit chemists found out proteins in light-harvesting complexes aren’t in order but still work super well! Discovered dat disorder can be good. Evolution is crazy, man! #efficiency #biology