Aug 17, 2019 | Updated: 07:24 AM EDT

Unlocking the Secrets of Photosynthetic Supercomplex Structure

May 27, 2019 12:15 PM EDT

Unlocking the Secrets of Photosynthetic Supercomplex Structure
(Photo : Yuval Mazor)

Through determining the structure of a very large photosynthetic supercomplex, a group of scientists from Arizona State University has made a significant move closer to unlocking the secrets of photosynthesis. The team laid out this important finding in their paper published in Nature Structural & Molecular Biology.

An assistant professor in the School of Molecular Sciences and the Biodesign Institute's Center for Applied Structural Discovery, Yuval Mazor said that supercomplexes are an association between antennae proteins and photochemical reaction centers that exist in all photosynthetic organisms. This specific one comes from cyanobacteria, the class (phyla) of bacteria whereby oxygen photosynthesis first emerged (a few billion years ago) and later evolved into all types of oxygen photosynthesis that we know today.

Plants, algae, and cyanobacteria use photosynthesis to produce oxygen and reduce carbon like carbohydrates, which builds and fuels the entire human's biosphere. Two pigment-protein complexes orchestrate the primary light reactions in oxygenic photosynthesis: photosystem (PSI) and photosystem II (PSII). Understanding how these photosystems work their magic is one of the long-sought goals of science.

There was a trigger of a revolution in structural biology through single-particle cryogenic electron microscopy (cryo-EM) in particular in the past few years and has become a newly dominant discipline. Through cryo-EM, researchers can take a look at biological structures that were not accessible just a few years ago and is now exposing structures of unprecedented complexity in great detail.

Ultimately, the experts in the School of Molecular Sciences and The College of Liberal Arts and Sciences at ASU have utilized this technique which enabled the elucidation of the structure of the PSI-IsiA complex. In the lab, cyanobacteria under low iron environment or excessive light fluxes produced this particular super-complex. However, in the "real world" iron exists at deficient concentrations and high light can be the rule rather than the exception. Consequently, PSI-IsiA is a popular form of photosystem I, one of the two essential engines of photosynthesis.

Researchers uncover the most crucial details of this enormous machine through the current structure. As the first example from the cyanobacteria branch of the membrane-embedded antenna proteins, it lays a path for evaluating the light-harvesting and photoprotection mechanism (from excess or fluctuating light conditions) in cyanobacteria.

When scientists understand the complexity and functions of the IsiA photosynthetic supercomplex, it will ultimately help to ensure that there is a stable energy supply on Earth and undoubtedly one of the central challenges of the 21st century.

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