# Taking Snapshots of the Water-Oxidation Reaction by the Mn4Ca Oxygen-Evolving Complex Using X-ray Crystallography and Spectroscopy

> **NIH NIH R01** · UNIVERSITY OF CALIF-LAWRENC BERKELEY LAB · 2020 · $566,500

## Abstract

Project Summary/Abstract
 Metalloproteins containing manganese in a redox-active role are involved in a variety of physiologically
important reactions of dioxygen metabolism. Perhaps the most complex is the Mn4CaO5 cluster that is involved
in the oxidation of water to dioxygen in photosystem II (PS II), an ~500 kDa multi-subunit membrane protein
complex. The water-oxidation reaction in PS II involves removal of four electrons from two water molecules, in
a stepwise manner by light-induced oxidation, to produce a molecule of oxygen. PS II and the Mn4CaO5 cluster
generate almost all of the dioxygen that supports aerobic life, and it is abundant in the atmosphere because of
its constant regeneration by the oxidation of water. The light-induced oxidation of water to dioxygen is one of
the most important chemical processes occurring on such a large scale in the biosphere.
 Although the structure of PS II and the chemistry at the catalytic site have been studied intensively,
understanding the sequence in the chemistry at atomic-scale from light absorption to water-oxidation requires
a new approach beyond the conventional steady state X-ray crystallography and X-ray spectroscopy at
cryogenic temperatures. Following the dynamic changes in the structure of PS II and the Mn4CaO5 cluster at
ambient conditions at physiological temperatures, while overcoming the severe X-ray damage to the redox
active center is key for deriving the mechanism. The intense and ultra-short femtosecond (fs) X-ray pulses
from a X-ray free electron laser (XFEL) provide an opportunity to overcome the current limitations in room
temperature data collection for biological samples at traditional X-ray sources. The fs X-ray pulses allow us to
acquire the signal before the sample is destroyed, thus making the light-induced snapshot study proposed here
possible.
 The objective of this proposal is to study the protein structure and dynamics of PS II with X-ray diffraction,
as well as the chemical structure and changes in the Mn4CaO5 cluster (charge and spin density, and
covalency) with X-ray spectroscopy during the light-driven process of PS II. We will use the XFEL facilities at
Stanford and elsewhere to collect X-ray diffraction and emission spectra simultaneously, and X-ray absorption
spectra of the Mn cluster in its native and intermediates states at room temperature in a time-resolved manner,
to capture short-lived intermediates and the step that includes the O-O bond formation. We have also started
studying the process of assembly of the Mn cluster as repair and assembly of PS II is an essential component
in nature.
 These studies have the potential to provide an unprecedented combination of correlated data between the
PS II protein, the co-factors, and the Mn4CaO5 cluster, providing the geometric and electronic structure and the
changes that occur during the catalytic cycle, all of which are necessary for a complete understanding of the
mechanism of water oxidation.
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## Key facts

- **NIH application ID:** 9921408
- **Project number:** 5R01GM055302-22
- **Recipient organization:** UNIVERSITY OF CALIF-LAWRENC BERKELEY LAB
- **Principal Investigator:** VITTAL YACHANDRA
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $566,500
- **Award type:** 5
- **Project period:** 1997-01-01 → 2023-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9921408

## Citation

> US National Institutes of Health, RePORTER application 9921408, Taking Snapshots of the Water-Oxidation Reaction by the Mn4Ca Oxygen-Evolving Complex Using X-ray Crystallography and Spectroscopy (5R01GM055302-22). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/9921408. Licensed CC0.

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