Pint of Postdoc Speaker Recap - Dr. Christopher J. Gisriel

“How to build a water oxidation enzyme”

Dr. Christopher J. Gisriel

Edited by: Aileen Fernandez

Photosynthetic organisms have evolved to use the energy from light to power water oxidation, allowing water to be used as an essentially endless fuel source. The enzyme responsible for this ability is photosystem II (PSII), which is of great research interest due to its implications in sustainable energy such as informing on the design of synthetic solar fuel catalysts. Water oxidation occurs in the active site of PSII which contains a metal cluster called the “oxygen-evolving complex” (OEC). Oxygen is released as a byproduct of water oxidation that can damage PSII, causing loss of function. To cope with this problem, the cell has developed a complex mechanism of assembly and repair, key aspects of PSII’s function that are largely unexplored.

To investigate these processes, Christopher Gisriel shared during the May 2021 Pint of Postdoc series how they altered PSII so that it resembled an assembly intermediate found in the cell by removing the OEC and some subunits, which they refer to as “apo-PSII”, and solved its molecular structure using cryo-electron microscopy. The surface of apo-PSII exhibits an open configuration and negative charge so that metal cations are directed into the active site for OEC assembly. When the OEC is absent from the active site, a unique configuration of nearby amino acids is observed which suggests a protein conformational change during OEC assembly. This structure provides a platform for future PSII studies that aim to understand OEC assembly by solving molecular structures using a bottom-up approach.