![]() This finding tells us that that may not just be an inevitable downside of biology, but organisms may have evolved to take advantage of it," Schlau-Cohen says. ![]() "Ordered organization is actually less efficient than the disordered organization of biology, which we think is really interesting because biology tends to be disordered. The researchers also found that proteins arranged in a lattice structure showed less efficient energy transfer than proteins that were arranged in randomly organized structures, as they usually are in living cells. "When a photon gets absorbed, you only have so long before that energy gets lost through unwanted processes such as nonradiative decay, so the faster it can get converted, the more efficient it will be," Schlau-Cohen says. For proteins farther apart, the transfer takes up to 15 picoseconds.įaster travel translates to more efficient energy transfer, because the longer the journey takes, the more energy is lost during the transfer. For proteins spaced closely together, the researchers found that it takes about 6 picoseconds for a photon of energy to travel between them. Disordered is betterīecause LH2 and LH3 absorb slightly different wavelengths of light, it is possible to use ultrafast spectroscopy to observe the energy transfer between them. They were also able to measure the distances between the light-harvesting proteins, which were on the scale of 2.5 to 3 nanometers. Using the cryo-electron microscope at the MIT.nano facility, the researchers could image their membrane-embedded proteins and show that they were positioned at distances similar to those seen in the native membrane. LH2 is the protein that is present during normal light conditions, and LH3 is a variant that is usually expressed only during low light conditions. By controlling the size of these membranes, known as nanodiscs, they were able to control the distance between two proteins embedded within the disks.įor this study, the researchers embedded two versions of the primary light-harvesting protein found in purple bacteria, known as LH2 and LH3, into their nanodiscs. ![]() To create an experimental setup where they could measure how energy travels between two proteins, the MIT team designed synthetic nanoscale membranes with a composition similar to those of naturally occurring cell membranes. However, studying how energy travels between these proteins has proven much more challenging because it requires positioning multiple proteins in a controlled way. Using ultrafast spectroscopy, a technique that uses extremely short laser pulses to study events that happen on timescales of femtoseconds to nanoseconds, scientists have been able to study how energy moves within a single one of these proteins. Within these cells, captured photons travel through light-harvesting complexes consisting of proteins and light-absorbing pigments such as chlorophyll. Energy captureįor this study, the MIT team focused on purple bacteria, which are often found in oxygen-poor aquatic environments and are commonly used as a model for studies of photosynthetic light-harvesting. Jianshu Cao, an MIT professor of chemistry, is also an author of the paper. are the lead authors of the paper, published in the Proceedings of the National Academy of Sciences. MIT postdocs Dihao Wang and Dvir Harris and former MIT graduate student Olivia Fiebig Ph.D. Our key finding is that the disordered organization of the light-harvesting proteins enhances the efficiency of that long-distance energy transduction," says Gabriela Schlau-Cohen, an associate professor of chemistry at MIT and the senior author of the new study. "In order for that antenna to work, you need long-distance energy transduction. For the first time, the researchers were able to measure the energy transfer between light-harvesting proteins, allowing them to discover that the disorganized arrangement of these proteins boosts the efficiency of the energy transduction. This transfer of energy through the light-harvesting complex occurs with extremely high efficiency: Nearly every photon of light absorbed generates an electron, a phenomenon known as near-unity quantum efficiency.Ī new study from MIT chemists offers a potential explanation for how proteins of the light-harvesting complex, also called the antenna, achieve that high efficiency.
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