Structural and electronic changes (oxidation states) of the Mn4Ca complex of photosystem II (PSII) in the water oxidation cycle are of prime interest. For all four transitions between semistable S-states (S0 → S1, S1 → S2, S2 → S3, and S3,4 → S0), oxidation state and structural changes of the Mn complex were investigated by X-ray absorption spectroscopy (XAS) not only at 20 K but also at room temperature (RT) where water oxidation is functional. Three distinct experimental approaches were used:  (1) illumination-freeze approach (XAS at 20 K), (2) flash-and-rapid-scan approach (RT), and (3) a novel time scan/sampling-XAS method (RT) facilitating particularly direct monitoring of the spectral changes in the S-state cycle. The rate of X-ray photoreduction was quantitatively assessed, and it was thus verified that the Mn ions remained in their initial oxidation state throughout the data collection period (>90%, at 20 K and at RT, for all S-states). Analysis of the complete XANES and EXAFS data sets (20 K and ...

Structural and oxidation state changes of the photosystem II manganese complex in four transitions of the water oxidation cycle (S0 --> S1, S1 --> S2, S2 --> S3, and S3,4 --> S0) characterized by X-ray absorption spectroscopy at 20 K and room temperature.

High-resolution analysis of Zn(2+) coordination in the alkaline phosphatase superfamily by EXAFS and x-ray crystallography.

We present an in situ small- and wide-angle X-ray scattering (SAXS/WAXS) and quick-scanning extended X-ray absorption fine-structure (QEXAFS) spectroscopy study on the crystallization of the metal-organic framework ZIF-7. In combination with DFT calculations, the self-assembly and growth of ZIF-7 microrods together with the chemical function of the crystal growth modulator (diethylamine) are revealed at all relevant length scales, from the atomic to the full crystal size.

The molecular pathway to ZIF-7 microrods revealed by in situ time-resolved small- and wide-angle X-ray scattering, quick-scanning extended X-ray absorption spectroscopy, and DFT calculations

https://backend.orbit.dtu.dk/ws/files/138123312/Fibrilartikel_revised3.pdf

Insulin fibrillation: The influence and coordination of Zn2+

Kti11p is a small, highly conserved CSL zinc finger-containing protein found in many eukaryotes. It was first identified as one of the factors required for maintaining the sensitivity of Saccharomyces cerevisiae to Kluyveromyces lactis zymocin. Then, it was found to be identical to Dph3, a protein required for diphthamide biosynthesis on eEF-2, the target of diphtheria toxin and Pseudomonas exotoxin A, in both yeast and higher eukaryotes. Furthermore, Kti11p/Dph3 was found to physically interact with core-Elongator, ribosomal proteins, eEF-2, two other proteins required for diphthamide modification on eEF-2, and DelGEF. Here, we determined the solution structure of Kti11p using NMR, providing the first structure of the CSL-class zinc-binding protein family. We present the first experimental evidence that Kti11p can bind a single Zn2+ ion by its four conserved cysteine residues. The major structure of Kti11p comprises a β sandwich as well as an α helix. Moreover, a structure-based similarity search suggest...

Solution structure of Kti11p from Saccharomyces cerevisiae reveals a novel zinc-binding module.

X-ray absorption spectroscopy (XAS), including extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) analysis, has been carried out at the Zn K edge of the N-terminal part of the integrase protein of the human immunodeficiency virus, type 2 (HIV-2), and of some zinc coordination compounds. In the presence of excess beta-mercaptoethanol, which was present in the NMR structure elucidation of the protein [Eijkelenboom et al. (1997), Curr. Biol. 7, 739-746; (2000), J. Biomol. NMR, 18, 119-28], the protein spectrum was nearly identical to that recorded in its absence. Comparison of the XANES of the protein with that of model compounds and literature data permits the conclusion that the Zn ion is four-coordinated. The major shell of the EXAFS provides evidence for a mixed (N or O as well as S) coordination sphere, while the minor shells indicate imidazole coordination. Our approach to the analysis of the EXAFS, including quantification of the imidazole by multiple scattering simulations with EXCURV92, was validated on the model compounds. An important result is that with multiple scattering simulations using restraints on the parameters of the imidazole rings the number of imidazoles and their orientation could be determined. The integrase spectra can be fitted with two sulfur ligands at 2.26 A (Debye-Waller-type factor 0.009 A(2)) and two imidazole ligands with the N atoms at 1.99 A (Debye-Waller-type factor 0.005 A(2)). The XAS-derived geometry is fully consistent with that found in the NMR structure determination and, allowing for the Volume contraction due to the temperature difference between the experiments, justifies the restraints applied in the structure calculation (Zn-S and Zn-N distances of 2.3 A and 2.0 A, respectively).

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Hans Friedrich Nolting

Papers

X-ray absorption spectroscopic studies of zinc in the N-terminal domain of HIV-2 integrase and model compounds.