Structural models of the manganese complex of photosystem II and mechanistic implications

Photosynthetic water oxidation and O2 formation are catalyzed by a Mn4Ca complex bound to the proteins of photosystem II (PSII). The catalytic site, including the inorganic Mn4CaOnHx core and its protein environment, is denoted as oxygen-evolving complex (OEC). Earlier and recent progress in the endeavor to elucidate the structure of the OEC is reviewed, with focus on recent results obtained by (i) X-ray spectroscopy (specifically by EXAFS analyses), and (ii) X-ray diffraction (XRD, protein crystallography). Very recently, an impressive resolution of 1.9 Å has been achieved by XRD. Most likely however, all XRD data on the Mn4CaOnHx core of the OEC are affected by X-ray induced modifications (radiation damage). Therefore and to address (important) details of the geometric and electronic structure of the OEC, a combined analysis of XRD and XAS data has been approached by several research groups. These efforts are reviewed and extended using an especially comprehensive approach. Taking into account XRD results on the protein environment of the inorganic core of the Mn complex, 12 alternative OEC models are considered and evaluated by quantitative comparison to (i) extended-range EXAFS data, (ii) polarized EXAFS of partially oriented PSII membrane particles, and (iii) polarized EXAFS of PSII crystals. We conclude that there is a class of OEC models that is in good agreement with both the recent crystallographic models and the XAS data. On these grounds, mechanistic implications for the Osingle bondO bond formation chemistry are discussed. This article is part of a Special Issue entitled: Photosystem II

Adoption of Electronic Medical Record-Based Decision Support for Otitis Media in Children

Substantial investment in electronic health records (EHRs) has provided an unprecedented opportunity to use clinical decision support (CDS) to increase guideline adherence. To inform efforts to maximize adoption, we characterized the adoption of an otitis media (OM) CDS system, the impact of performance feedback on adoption, and the effects of adoption on guideline adherence

A Potential New Pathway for Staphylococcus aureus Dissemination: The Silent Survival of S. aureus Phagocytosed by Human Monocyte-Derived Macrophages

Although considered to be an extracellular pathogen, Staphylococcus aureus is able to invade a variety of mammalian, non-professional phagocytes and can also survive engulfment by professional phagocytes such as neutrophils and monocytes. In both of these cell types S. aureus promptly escapes from the endosomes/phagosomes and proliferates within the cytoplasm, which quickly leads to host cell death. In this report we show that S. aureus interacted with human monocyte-derived macrophages in a very different way to those of other mammalian cells. Upon phagocytosis by macrophages, S. aureus persisted intracellularly in vacuoles for 3–4 days before escaping into the cytoplasm and causing host cell lysis. Until the point of host cell lysis the infected macrophages showed no signs of apoptosis or necrosis and were functional. They were able to eliminate intracellular staphylococci if prestimulated with interferon-γ at concentrations equivalent to human therapeutic doses. S. aureus survival was dependent on the alternative sigma factor B as well as the global regulator agr, but not SarA. Furthermore, isogenic mutants deficient in α-toxin, the metalloprotease aureolysin, protein A, and sortase A were efficiently killed by macrophages upon phagocytosis, although with different kinetics. In particular α-toxin was a key effector molecule that was essential for S. aureus intracellular survival in macrophages. Together, our data indicate that the ability of S. aureus to survive phagocytosis by macrophages is determined by multiple virulence factors in a way that differs considerably from its interactions with other cell types. S. aureus persists inside macrophages for several days without affecting the viability of these mobile cells which may serve as vehicles for the dissemination of infection

Strukturelle Modelle basierend auf Röntgenabsorptionsspektroskopie

1\. Introduction 2\. Structural models of the Mn complex - Present status 3\. Improved distance resolution by extended-range EXAFS 4\. Modeling the Mn complex 5\. Evaluation of OEC models 6\. Implications and future directions A. Appendix B. Atom coordinates of modelsThe manganese complex (Mn complex) bound to the protein complex photosystem II (PSII) is responsible for water oxidation and O2 formation in photosynthesis. Due to its important role, the structure of the Mn complex is of very high interest. In this thesis, extended-range EXAFS spectra measured for PSII membrane particles are presented which allow for significantly higher distance resolution in contrast to standard EXAFS at the Mn-edge. Further, recently in literature published models of the Mn complex are discussed in regard to these data as well as in literature published EXAFS spectra and XRD results. The EXAFS data from literature taken into account were measured (i) on partially oriented PSII membrane particles under different angles between the electric- field vector of the X-ray beam and the sample normal and (ii) on PSII crystals for all three axes of the unit cell. For the structural models, EXAFS spectra are calculated and compared to these experimental results. Based on the experimental EXAFS data and starting from an XRD structure of PSII, for the first time models of the Mn complex are developed which are in agreement with EXAFS measurements on both partially oriented PSII samples and PSII crystals.Der Mangankomplex des Photosystem II (PSII) ist in der Photosynthese verantwortlich für die Oxidation von Wasser und Bildung von molekularem Sauerstoff. Auf Grund dieser wichtigen Funktion ist die Aufklärung der Struktur des Mangankomplexes von herausragender Bedeutung. In dieser Arbeit werden sogenannte "Extended-range-EXAFS"-Spektren von PSII-Membranpartikeln präsentiert. Diese Daten ermöglichen im Vergleich zu Standard-EXAFS-Spektren an der Mn-Kante eine deutliche höhere Distanzauflösung. Des Weiteren werden einige in den letzten Jahren in der Literatur veröffentlichte Modelle des Mangankomplexes im Hinblick auf diese Daten als auch weiterer in der Literatur veröffentlichter EXAFS-Spektren analysiert. Hierzu wurden EXAFS-Spektren aus der Literatur verwendet, die (i) an partiell-orientieren PSII-Membranpartikeln unter verschiedenen Winkeln zwischen dem Vektor des elektrischen Feldes des Röntgenstrahls und der Probennormalen sowie (ii) an PSII-Kristallen für alle drei Achsen der Einheitszelle gemessen wurden. Für alle betrachteten Modelle wurden EXAFS-Spektren simuliert und mit diesen experimentellen Resultaten verglichen. Basierend auf den experimentellen EXAFS-Daten und ausgehend von Ergebnissen der Röntgenstrukturanalyse des PSII werden erstmalig Modelle des Mangankomplexes entwickelt, die in Übereinstimmung mit den EXAFS-Messungen sowohl an partiell orientierten PSII-Proben als auch PSII-Kristallen sind

On the structure of the manganese complex of photosystem II: extended-range EXAFS data and specific atomic-resolution models for four S-states

The water-oxidizing manganese complex bound to the proteins of photosystem II (PSII) was studied by X-ray absorption spectroscopy on PSII membrane particles. An extended range for collection of extended X-ray absorption fine-structure (EXAFS) data was used (up to 16.6 Å−1). The EXAFS suggests the presence of two Mn–Mn distances close to 2.7 Å (per Mn4Ca complex); the existence of a third Mn–Mn distance below 2.9 Å is at least uncertain. Interestingly, a distance of 3.7 Å is clearly resolved in the extended-range data and tentatively assigned to a Mn–Mn distance. Taking into account the above EXAFS results (inter alia), we present a model for the structure of the PSII manganese complex, which differs from previous atomic-resolution models. Emphasizing the hypothetical character, we propose for all semi-stable S-states: (i) a structure of the Mn4Ca(μ-O)n core, (ii) a model of the amino acid environment, and (iii) assignments of distinct Mn oxidation states to all the individual Mn ions. This specific working model may permit discussion, verification and invalidation of its various features in comparison with experimental and theoretical findings