ASU Team Unlocks Structure Of Key Photosynthesis Supercomplex

By Nicholas Gerbis
Published: Friday, June 7, 2019 - 9:42am
Updated: Monday, June 10, 2019 - 8:10am

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The overall structure of the PSI-IsiA supercomplex.

By changing solar energy into products usable by plants and animals, photosynthesis provides the basis of nearly all life on Earth.

Now, an Arizona State University team has described the complex structure of one of its key components, a supercomplex found in cyanobacteria.

The research appears in the journal "Nature Structural & Molecular Biology."

"The past year is the first time we have a molecular-level description of one of the most complicated light harvesting systems in biology," said co-author Yuval Mazor, a structural biologist in ASU's School of Molecular Sciences.

Photosynthesis occurs in large complexes of proteins and pigments called photosystems. Photosystems receive energy from light-harvesting complexes called antennae, which consist of proteins that bind pigments like chlorophyll, xanthophylls and carotenes. Together, these form supercomplexes containing hundreds of pigments.

When cyanobacteria are stressed by a lack of iron, they produce a special antenna called iron-stress-induced protein A (IsiA). IsiA can also be expressed under other stress conditions, such as high light levels.

Because many of the environments in which cyanobacteria live are iron-poor and have high light conditions, IsiA is a very common part of their photosynthetic systems.

ASU
Pigment organization in PSI-IsiA: Chlorophylls are colored green and carotenoids in pink.

Researchers have long known about IsiA, but its molecular structure remained a mystery until higher resolution electron microscopes let ASU researchers unravel this system of 700 molecules.

Mazor said scientists have made great strides in understanding photosynthesis, but have far to go before they can reliably manipulate the process — to improve crop yields, for example.

"We don't have good predictive ability of what will happen if we change certain parts of the systems, and that's sort of the knowledge that we're after right now. And of course we don't know what we don't know," he said.

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