2026-05-21T18:02:18Zhttps://keep.lib.asu.edu/oai/requestoai:keep.lib.asu.edu:node-1541212024-12-20T18:25:12Zoai_pmh:alloai_pmh:repo_items154121
https://hdl.handle.net/2286/R.I.36383
http://rightsstatements.org/vocab/InC/1.0/
All Rights Reserved
2015
xvi, 212 pages : illustrations (some color)
Doctoral Dissertation
Academic theses
Text
eng
Basu, Shibom, 1988-
Fromme, Petra
Spence, John C.H.
Wolf, George
Ros, Robert
Fromme, Raimund
Arizona State University
Vita
Partial requirement for: Ph.D., Arizona State University, 2015
Includes bibliographical references (pages 198-211)
Field of study: Chemistry
Photosystem II (PSII) is a large protein-cofactor complex. The first step in<br/><br/>photosynthesis involves the harvesting of light energy from the sun by the antenna (made<br/><br/>of pigments) of the PSII trans-membrane complex. The harvested excitation energy is<br/><br/>transferred from the antenna complex to the reaction center of the PSII, which leads to a<br/><br/>light-driven charge separation event, from water to plastoquinone. This phenomenal<br/><br/>process has been producing the oxygen that maintains the oxygenic environment of our<br/><br/>planet for the past 2.5 billion years.<br/><br/>The oxygen molecule formation involves the light-driven extraction of 4 electrons<br/><br/>and protons from two water molecules through a multistep reaction, in which the Oxygen<br/><br/>Evolving Center (OEC) of PSII cycles through 5 different oxidation states, S0 to S4.<br/><br/>Unraveling the water-splitting mechanism remains as a grant challenge in the field of<br/><br/>photosynthesis research. This requires the development of an entirely new capability, the<br/><br/>ability to produce molecular movies. This dissertation advances a novel technique, Serial<br/><br/>Femtosecond X-ray crystallography (SFX), into a new realm whereby such time-resolved<br/><br/>molecular movies may be attained. The ultimate goal is to make a “molecular movie” that<br/><br/>reveals the dynamics of the water splitting mechanism using time-resolved SFX (TRSFX)<br/><br/>experiments and the uniquely enabling features of X-ray Free-Electron Laser<br/><br/>(XFEL) for the study of biological processes.<br/><br/>This thesis presents the development of SFX techniques, including development of<br/><br/>new methods to analyze millions of diffraction patterns (~100 terabytes of data per XFEL<br/><br/>experiment) with the goal of solving the X-ray structures in different transition states.<br/><br/>ii<br/><br/>The research comprises significant advancements to XFEL software packages (e.g.,<br/><br/>Cheetah and CrystFEL). Initially these programs could evaluate only 8-10% of all the<br/><br/>data acquired successfully. This research demonstrates that with manual optimizations,<br/><br/>the evaluation success rate was enhanced to 40-50%. These improvements have enabled<br/><br/>TR-SFX, for the first time, to examine the double excited state (S3) of PSII at 5.5-Å. This<br/><br/>breakthrough demonstrated the first indication of conformational changes between the<br/><br/>ground (S1) and the double-excited (S3) states, a result fully consistent with theoretical<br/><br/>predictions.<br/><br/>The power of the TR-SFX technique was further demonstrated with proof-of principle<br/><br/>experiments on Photoactive Yellow Protein (PYP) micro-crystals that high<br/><br/>temporal (10-ns) and spatial (1.5-Å) resolution structures could be achieved.<br/><br/>In summary, this dissertation research heralds the development of the TR-SFX<br/><br/>technique, protocols, and associated data analysis methods that will usher into practice a<br/><br/>new era in structural biology for the recording of ‘molecular movies’ of any biomolecular<br/><br/>process.
Biophysics
Data Analysis
Photosystem II
SFX
Time-resolved crystallography
XFEL
Photosynthesis
Femtosecond lasers
Crystallography
Photoelectrochemistry
Water--Electrolysis.
Time-resolved crystallography using X-ray free-electron laser