Rapid-Scan Time-Resolved ATR-FTIR Study on the Photoassembly of the Water-Oxidizing Mn4CaO5 Cluster in Photosystem II.
Akihiko SatoYuki NakanoShin NakamuraTakumi NoguchiPublished in: The journal of physical chemistry. B (2021)
The catalytic center of photosynthetic water oxidation, the Mn4CaO5 cluster, is assembled in photosystem II (PSII) through a light-driven process called photoactivation, whose mechanism remains elusive. Here, we used rapid-scan time-resolved Fourier transform infrared (FTIR) spectroscopy combined with the attenuated total reflection (ATR) technique to monitor the photoactivation process. Rapid-scan ATR-FTIR spectra of apo-PSII with Mn2+ upon flash illumination showed spectral features typical of carboxylate stretching vibrations, which were attributed to two carboxylate ligands, D1-D170 and D1-E189, by quantum chemical calculations. The FTIR signal decayed with a time constant of ∼0.7 s, showing that the subsequent "dark rearrangement" step occurred with a low quantum yield and Mn3+ ions were mostly released during this decay. Simulation of the kinetic process provided a slow intrinsic rate of the dark rearrangement, which was attributed to a large protein conformational change. The photoassembly mechanism of the Mn4CaO5 cluster is proposed based on these findings.
Keyphrases
- molecular dynamics
- room temperature
- computed tomography
- transition metal
- metal organic framework
- energy transfer
- density functional theory
- dna damage response
- loop mediated isothermal amplification
- molecular dynamics simulations
- single molecule
- electron transfer
- optical coherence tomography
- dual energy
- small molecule
- monte carlo
- mass spectrometry
- binding protein