In portrait: nature’s master thief as a young enzyme

At the heart of photosynthesis, the process by which plants and certain microorganisms produce Earth’s oxygen, there is a monumental act of thievery.

An enigmatic enzyme known as Photosystem II steals electrons from water, uses them as fuel, and leaves in its wake all of the air we breathe. It is a chemical sleight of hand that scientists have tried to mimic for decades.

Now, researchers at Yale and the University of California-Riverside say they’ve stolen a look at how Photosystem II itself forms. What they found may lead to insights for designing new solar energy systems.

In a study in the journal Joule, researchers led by Yale’s Gary Brudvig described how they broke the enzyme down to its most rudimentary core. Brudvig is the Benjamin Silliman Professor of Chemistry in the Faculty of Arts and Sciences and director of the Energy Sciences Institute at Yale’s West Campus.

“Although the more complex, mature molecular structure of Photosystem II has been known for 20 years, it still only leaves us with a snapshot of its structure in its most advanced state,” Brudvig said. “We really don’t understand how it is put together or how it initiates its function of removing electrons from water, a process called photoactivation. Our team set out to understand how Photosystem II is made by the cell.”

Using Yale’s cryo-electron microscopy facilities, the researchers created the highest-resolution picture to date of the enzyme’s early structure. At this level of detail researchers could see where individual amino acids were located in Photosystem II and how they differ from the mature state of the enzyme.

“We gained valuable insight into how early precursor states of Photosystem II look inside of the cell while it is being built, and even how it probably attracts some of the components that make up the mature state,” said Christopher Gisriel, a postdoctoral associate in chemistry at Yale and first author of the study.

The researchers plan to reconstruct Photosystem II sequentially in order to further understand all of the steps necessary for it to conduct its electron larceny.

Co-authors of the study include Kaifeng Zhou, Hao-Li Huang, and Yong Xiong, all of Yale, and Richard Debus from the University of California-Riverside.

The U.S. Department of Energy’s Office of Basic Energy Sciences funded the research.