The role of Ca and protein scaffolding in the formation of nature's water oxidizing complex.

Photosynthetic O evolution is catalyzed by the MnCaO cluster of the water oxidation complex of the photosystem II (PSII) complex. The photooxidative self-assembly of the MnCaO cluster, termed photoactivation, utilizes the same highly oxidizing species that drive the water oxidation in order to drive the incorporation of Mn into the high-valence MnCaO cluster. This multistep process proceeds with low quantum efficiency, involves a molecular rearrangement between light-activated steps, and is prone to photoinactivation and misassembly.

Role of zinc transporter ZIP12 in susceptibility-weighted brain magnetic resonance imaging (MRI) phenotypes and mitochondrial function.

Brain zinc dysregulation is linked to many neurological disorders. However, the mechanisms regulating brain zinc homeostasis are poorly understood. We performed secondary analyses of brain MRI GWAS and exome sequencing data from adults in the UK Biobank.

Pan-Genomic and Polymorphic Driven Prediction of Antibiotic Resistance in .

The are a genetically diverse genus of emerging pathogens that exhibit multidrug resistance to a range of common antibiotics. Two representative species, and , were phenotypically tested to determine minimum inhibitory concentrations (MICs) for five antibiotics. Ultra-long read sequencing with Oxford Nanopore Technologies (ONT) and subsequent assembly produced complete, gapless circular genomes for each strain.

The D1-D61N mutation in Synechocystis sp. PCC 6803 allows the observation of pH-sensitive intermediates in the formation and release of O₂ from photosystem II.

The active site of photosynthetic water oxidation by Photosystem II (PSII) is a manganese-calcium cluster (Mn(4)CaO(5)). A postulated catalytic base is assumed to be crucial. CP43-Arg357, which is a candidate for the identity of this base, is a second-sphere ligand of the Mn(4)-Ca cluster and is located near a putative proton exit pathway, which begins with residue D1-D61.

Participation of glutamate-354 of the CP43 polypeptide in the ligation of manganese and the binding of substrate water in photosystem II.

In the current X-ray crystallographic structural models of photosystem II, Glu354 of the CP43 polypeptide is the only amino acid ligand of the oxygen-evolving Mn(4)Ca cluster that is not provided by the D1 polypeptide. To further explore the influence of this structurally unique residue on the properties of the Mn(4)Ca cluster, the CP43-E354Q mutant of the cyanobacterium Synechocystis sp. PCC 6803 was characterized with a variety of biophysical and spectroscopic methods, including polarography, EPR, X-ray absorption, FTIR, and mass spectrometry.

Spectroscopic and functional characterizations of cyanobacterium Synechocystis PCC 6803 mutants on and near the heme axial ligand of cytochrome b559 in photosystem II.

The functional role of cytochrome (cyt) b(559) in photosystem II (PSII) was investigated in H22K alpha and Y18S alpha cyt b(559) mutants of the cyanobacterium Synechocystis sp. PCC6803. H22K alpha and Y18S alpha cyt b(559) mutant carries one amino acid substitution on and near one of heme axial ligands of cyt b(559) in PSII, respectively.

Loss of peripheral polypeptides in the stromal side of photosystem I by light-chilling in cucumber leaves.

Photosystem I (PSI) is severely damaged by chilling at 4 degrees C in low light, especially in the chilling sensitive plant cucumber. To investigate the early events in PSI photoinhibition, we examined structural changes in the level of pigment-protein complexes in cucumber leaves in comparison with pea leaves. The complexes were separated on a native green gel and an increase in the intensity of a band was observed only in light-chilled cucumber leaves.

Assembly and disassembly of the photosystem II manganese cluster reversibly alters the coupling of the reaction center with the light-harvesting phycobilisome.

The light-driven oxidative assembly of Mn (2+) ions into the H 2O oxidation complex (WOC) of the photosystem II (PSII) reaction center is termed photoactivation. The fluorescence yield characteristics of Synechocystis sp. PCC6803 cells undergoing photoactivation showed that basal fluorescence, F 0, exhibited a characteristic decline when red, but not blue, measuring light was employed.

Photoassembly of the manganese cluster in mutants perturbed in the high affinity Mn-binding site of the H2O-oxidation complex of photosystem II.

The light-driven, oxidative assembly of Mn2+ ions into the H2O-oxidation complex (WOC) of the photosystem II (PSII) reaction center is termed photoactivation and culminates in the formation of the oxygen-evolving (Mn4-Ca) center of the WOC. Initial binding and photooxidation of Mn2+ to the apoprotein is critically dependent upon aspartate 170 of the D1 protein (D1-D170) of the high affinity Mn site [Nixon and Diner (1992) Biochemistry 31, 942-948]. Three O2-evolving mutant strains of Synechocystis, D1-D170E, D1-D170H, and D1-D170V, were studied in terms of the kinetics of photoactivation under both continuous and flashing light.

Glutamate-354 of the CP43 polypeptide interacts with the oxygen-evolving Mn4Ca cluster of photosystem II: a preliminary characterization of the Glu354Gln mutant.

In the recent X-ray crystallographic structural models of photosystem II, Glu354 of the CP43 polypeptide is assigned as a ligand of the O2-evolving Mn4Ca cluster. In this communication, a preliminary characterization of the CP43-Glu354Gln mutant of the cyanobacterium Synechocystis sp. PCC 6803 is presented.

Mutation of arginine 357 of the CP43 protein of photosystem II severely impairs the catalytic S-state cycle of the H2O oxidation complex.

Basic amino acid side chains situated in active sites may mediate critical proton transfers during an enzymatic catalytic cycle. In the case of photosynthetic water oxidation, a strong base is postulated to facilitate the deprotonation of the active site Mn4-Ca cluster, thereby allowing the otherwise thermodynamically constrained transfer of an electron away from the Mn4-Ca cluster to the oxidized redox active tyrosine radical, YZ*, generated by photosynthetic charge separation. Arginine 357 of the CP43 polypeptide may be located in the second coordination shell of the O2-evolving Mn4-Ca cluster of photosystem II (PSII) according to current structural models.

Engineered ectopic expression of the psbA gene encoding the photosystem II D1 protein in Synechocystis sp. PCC6803.

A genetic vector-recipient system was developed to engineer expression of the wild-type psbA2 gene encoding the photosystem II (PSII) D1 protein only from a non-native location (ectopic) in the Synechocystis sp. PCC6803 and the result was a new strain, designated MK1. While MK1 accumulates near normal levels of PSII under low light conditions, it is very sensitive to photoinhibition.

Multiflash experiments reveal a new kinetic phase of photosystem II manganese cluster assembly in Synechocystis sp. PCC6803 in vivo.

The assembly of Mn(2+) ions into the H(2)O oxidation complex (WOC) of the photosystem II (PSII) reaction center is a light-driven process, termed photoactivation. According to the "two-quantum" model, photoactivation involves two light-driven charge separations coupled to the photooxidation of Mn(2+) in order to form the first stable intermediate in a process that culminates in the oxidative assembly of four Mn(2+) ions and one Ca(2+) ion to form the active, higher valence (Mn(4)-Ca) center of the WOC. To better define the kinetics of the dark rearrangement and to gain some understanding of the basis for the very low quantum yield of the overall process, photoactivation experiments, involving different flash patterns, were conducted with Synechocystis sp.

Photoinhibition of photosystem I is accelerated by dimethyldithiocarbamate, an inhibitor of superoxide dismutase, during light-chilling of spinach leaves.

In vivo photoinhibition of photosystem I (PS I) was investigated at chilling temperature using the leaves of the chilling-resistant spinach plant treated with an inhibitor of superoxide dismutase, diethyldithiocarbamate (DDC). When spinach leaves were treated with DDC during chilling at 4 degrees C for 12 h with a light intensity of 120 micromol m(-2) s(-1), the activity of PS I and the content of iron-sulfur centers declined to about 50% and 25% of the non-DDC-treated controls, respectively. A native green gel analysis of thylakoid membranes isolated from the DDC-treated leaves resolved a novel chlorophyll-protein complex, which was identified as the light-harvesting complex I (LHC I)-deficient PS I complex when examined by 77 K fluorescence spectroscopy and two-dimensional sodium dodecyl sulfate gel electrophoresis.