Isolation and characterization of oxygen-evolving thylakoid membranes and photosystem II particles from a glaucocystophyte, Cyanophora paradoxa

Conditions for preparing oxygen-evolving thylakoid membranes and PSII complexes, and those for observing the PSII activity were investigated in a glaucocystophyte, Cyanophora paradoxa. The active thylakoid membranes were isolated either with a medium containing glycerol or with that containing high concentrations of sucrose, phosphate, and citrate. Active PSII particles were solubilized by octyl-beta-D-glucoside from thylakoid membranes and were separated by sucrose density gradient centrifugation. The thylakoid membranes and PSII particles showed an oxygen-evolving activity only in high-ionic-strength media. The extrinsic 33 kDa protein (PsbO) and the cytochrome c(550) (PsbV) were found to be present in the PSII particles as in cyanobacteria or red algae, but no 12 kDa protein (PsbU) was detected. The PsbO protein was classified as a land-plant type by its N-terminal amino acid sequence.     

Application of Pseudomurein Endoisopeptidase to Fluorescence In Situ Hybridization of Methanogens within the Family Methanobacteriaceae

In situ detection of methanogens within the family Methanobacteriaceae is sometimes known to be unsuccessful due to the difficulty in permeability of oligonucleotide probes. Pseudomurein endoisopeptidase (Pei), a lytic enzyme that specifically acts on their cell walls, was applied prior to 16S rRNA-targeting fluorescence in situ hybridization (FISH). For this purpose, pure cultured methanogens within this family, Methanobacterium bryantii, Methanobrevibacter ruminantium, Methanosphaera stadtmanae, and Methanothermobacter thermautotrophicus together with a Methanothermobacter thermautotrophicus-containing syntrophic acetate-oxidizing coculture, endosymbiotic Methanobrevibacter methanogens within an anaerobic ciliate, and an upflow anaerobic sludge blanket (UASB) granule were examined. Even without the Pei treatment, Methanobacterium bryantii and Methanothermobacter thermautotrophicus cells are relatively well hybridized with oligonucleotide probes. However, almost none of the cells of Methanobrevibacter ruminantium, Methanosphaera stadtmanae, cocultured Methanothermobacter thermautotrophicus, and the endosymbiotic methanogens and the cells within UASB granule were hybridized. Pei treatment was able to increase the probe hybridization ratio in every specimen, particularly in the specimen that had shown little hybridization. Interestingly, the hybridizing signal intensity of Methanothermobacter thermautotrophicus cells in coculture with an acetate-oxidizing H₂-producing syntroph was significantly improved by Pei pretreatment, whereas the probe was well hybridized with the cells of pure culture of the same strain. We found that the difference is attributed to the differences in cell wall thicknesses between the two culture conditions. These results indicate that Pei treatment is effective for FISH analysis of methanogens that show impermeability to the probe.     

Structural basis of the broad substrate tolerance of the antibody 7B9-catalyzed hydrolysis of p-nitrobenzyl esters

Catalytic antibody 7B9, which was elicited against p-nitrobenzyl phosphonate transition-state analogue (TSA) 1, hydrolyzes a wide range of p-nitrobenzyl monoesters and thus shows broad substrate tolerance. To reveal the molecular basis of this substrate tolerance, the 7B9 Fab fragment complexed with p-nitrobenzyl ethylphosphonate 2 was crystallized and the three-dimensional structure was determined. The crystal structure showed that the strongly antigenic p-nitrobenzyl moiety occupied a relatively shallow antigen-combining site and therefore the alkyl moiety was located outside the pocket. These results support the observed broad substrate tolerance of 7B9 and help rationalize how 7B9 can catalyze various p-nitrobenzyl ester derivatives. The crystal structure also showed that three amino acid residues (Asn^H33, Ser^H95, and Arg^L96) were placed in key positions to form hydrogen bonds with the phosphonate oxygens of the transitions-state analogue. In addition, the role of these amino acid residues was examined by site-directed mutagenesis to alanine: all mutants (Asn^H33Ala, Ser^H95Ala, and Arg^L96Ala) showed no detectable catalytic activity. Coupling the findings from our structural studies with these mutagenesis results clarified the structural basis of the observed broad substrate tolerance of antibody 7B9-catalyzed hydrolyses. Our findings provide new strategies for the generation of catalytic antibodies that accept a broad range of substrates, aiding their practical application in synthetic organic chemistry.     

Prevalence of sleep disorders and their impact on academic performance in medical students/University of Duhok

Full-time students experiencing high levels of stress due to a high bulk of teaching materials and academic performance demands are the most susceptible population class for different types of sleep disorders. The current study examined the prevalence of sleep disorders and their impacts on academic performance of a random sample of medical college students. In this regard, a random sample of 316 medical students of a large public university in Iraq participated in a cross-sectional study. The participants completed the SLEEP-50 self-reported questionnaire and questions about socio-demographic factors. The variables set included sleep apnea, insomnia, narcolepsy, restless legs syndrome, circadian rhythm sleep disorder, sleepwalking, nightmares, grade point average, and some socio-demographic characteristics. The study showed that to some extent, the students suffer from different types of sleep disorders with no substantial difference between males and females. Students with worse level of sleep disorders had a lower grade point average compared with those with normal sleep patterns (p = 0.001). The study confirmed that students with sleep disorders had poorer academic performance at college.

     

A comparative study of the biomass properties of Erianthus and sugarcane: lignocellulose structure,alkaline delignification rate,and enzymatic saccharification efficiency

A comprehensive understanding of the structure and properties of gramineous lignocelluloses is needed to facilitate their uses in biorefinery. In this study, lignocelluloses from fractionated internode tissues of two taxonomically close species, Erianthus arundinaceus and sugarcane (Saccharum spp.), were characterized. Our analyses determined that syringyl (S) lignins were predominant over guaiacyl (G) or p-hydroxyphenyl (H) lignins in sugarcane tissues; on the other hand, S lignin levels were similar to those of G lignin in Erianthus tissues. In addition, tricin units were detected in sugarcane tissues, but not in Erianthus tissues. Distributions of lignin inter-monomeric linkage types were also different in Erianthus and sugarcane tissues. Alkaline treatment removed lignins from sugarcane tissues more efficiently than Erianthus tissues, resulting in a higher enzymatic digestibility of sugarcane tissues compared with Erianthus tissues. Our data indicate that Erianthus biomass displayed resistance to alkaline delignification and enzymatic digestion.     

Tandem Duplications in the C-terminal Domain of the Mesotocin Receptor Exclusively Identified Among East Eurasian Thrushes

Mesotocin is a neurohypophyseal hormone found in some non-mammalian vertebrates, including birds, reptiles, and amphibians. In this study, we identified and characterized 18-amino acid duplications in the C-terminal domain of the mesotocin receptor (MTR), specifically found in Turdus thrushes (Aves: Passeriforms: Turdidae). These duplicated elements are located in the distal part of the C-terminal tails of MTR and consist of amino acids that are highly conserved among major vertebrates. Intraspecific polymorphisms in a variable number of tandem duplications are commonly found in East Eurasian Turdus, but not in any other genus of Turdidae. Moreover, the genus Turdus can be further classified into 2 groups according to the presence or absence of a 3-amino acid deletion just adjacent to the putative palmitoylation site in the cytoplasmic C-terminal tail. The phylogeny presented here strongly supports the conspecific group of 4 East Eurasian thrushes (Turdus pallidus, T. chrysolaus, T. obscurus, and T. celaenops). Our findings, therefore, provide a new synapomorphy that can be used for phylogenetic assumptions and shed a light on the history of diversification within Eurasian Turdus clades.     

Spectral properties of a divinyl chlorophyll a harboring mutant of Synechocystis sp. PCC6803

A divinyl chlorophyll (DV-Chl) a harboring mutant of Synechocystis sp. PCC 6803, in which chlorophyll species is replaced from monovinyl(normal)-Chl a to DV-Chl a, was characterized. The efficiency of light utilization for photosynthesis was decreased in the mutant. Absorption spectra at 77 K and their fourth derivative analyses revealed that peaks of each chlorophyll forms were blue-shifted by 1–2 nm, suggesting lowered stability of chlorophylls at their binding sites. This was also true both in PSI and PSII complexes. On the other hand, fluorescence emission spectra measured at 77 K were not different between wild type and the mutant. This indicates that the mode of interaction between chlorophyll and its binding pockets responsible for emitting fluorescence at 77 K is not altered in the mutant. P700 difference spectra of thylakoid membranes and PSI complexes showed that the spectrum in Soret region was red-shifted by 7 nm in the mutant. This is a characteristic feature of DV-Chl a. Microenvironments of iron–sulfur center of a terminal electron acceptor of PSI complex, P430, were practically the same as that of wild type.