Thylakoid membrane dynamics and state transitions in Chlamydomonas reinhardtii under elevated temperature

Photosynthesis Research - Moderately elevated temperatures can induce state transitions in higher plants by phosphorylation of light-harvesting complex II (LHCII). In this study, we exposed...     

Formulation and Evaluation of Gastroretentive Dosage Forms of Clarithromycin

The purpose of this research was to develop the hydrodynamically balanced delivery system of Clarithromycin (CLA) which, after oral administration should have the ability to prolong gastric residence time with the desired in vitro release profile for the localized action in the stomach, in the treatment of Helicobacter pylori (H.pylori) mediated peptic ulcer. By applying wet granulation technique floating tablets of Clarithromycin were prepared. The proportion of sodium bicarbonate was varied to get the least possible lag time, also the polymer part varied to get the desired release. In vivo radiographic studies were performed with Barium sulphate loaded formulation to justify the increased gastric residence time of the dosage form in the stomach, based on the floating principle. The formulation developed using 66.2% Clarithromycin, 12% HPMC K4M polymer, 8% sodium bicarbonate gave floating lag time less than 3 min with a floating time of 12 h, and an in vitro release profile very near to the desired release. X-ray studies showed the enhanced gastric residence time of the tablet to 220 ± 30 min. The mechanism of release of Clarithromycin from the floating tablets is anomalous diffusion transport and follows zero order kinetics. In vivo radiographic studies suggest that the tablet has increased gastric residence time for the effective localized action of the antibiotic (Clarithromycin) in the treatment of H.pylori mediated peptic ulcer.     

Molecular genetic analysis of an SNF2/brahma-related gene in Tetrahymena thermophila suggests roles in growth and nuclear development

We used a reverse genetic approach to identify three members of the SNF2 superfamily of chromatin remodeling genes in the ciliated protozoan Tetrahymena thermophila in order to investigate possible functions of ATP-dependent chromatin remodeling factors in growth and nuclear development. Comparative sequence analysis of the gene product of the Tetrahymena brahma-related gene (TtBRG1) indicates it is a member of the SNF2/BRM subgroup of the SNF2 superfamily. Northern analysis suggests that TtBRG1 has roles in growth and nuclear development in Tetrahymena. Indirect immunofluorescence analysis during nuclear development indicates that TtBrg1p localizes to both the parental and developing macronucleus of Tetrahymena during the time period corresponding to genome rearrangements. We generated germ line knockout heterokaryons for TtBRG1 and demonstrated that expression of the gene is required to complete nuclear development of Tetrahymena. In addition, the formation of distinct Pdd1p-containing structures is disturbed during the late stages of conjugation in TtBRG1 germ line knockout heterokaryons. We discuss these results in light of possible roles of SNF2-related proteins in growth and nuclear development of Tetrahymena.     

Two distinct ferritin-like molecules in Pseudomonas aeruginosa: the product of the bfrA gene is a bacterial ferritin (FtnA) and not a bacterioferritin (Bfr)

Two distinct types of ferritin-like molecules often coexist in bacteria, the heme binding bacterioferritins (Bfr) and the non-heme binding bacterial ferritins (Ftn). The early isolation of a ferritin-like molecule from Pseudomonas aeruginosa suggested the possibility of a bacterioferritin assembled from two different subunits [Moore, G. R., et al. (1994) Biochem. J. 304, 493-497]. Subsequent studies demonstrated the presence of two genes encoding ferritin-like molecules in P. aeruginosa, designated bfrA and bfrB, and suggested that two distinct bacterioferritins may coexist [Ma, J.-F., et al. (1999) J. Bacteriol. 181, 3730-3742]. In this report, we present structural evidence demonstrating that the product of the bfrA gene is a ferritin-like molecule not capable of binding heme that harbors a catalytically active ferroxidase center with structural properties similar to those characteristic of bacterial and archaeal Ftns and clearly distinct from those of the ferroxidase center typical of Bfrs. Consequently, the product of the bfrA gene in P. aeruginosa is a bacterial ferritin, which we propose should be termed Pa FtnA. These results, together with the previous characterization of the product of the bfrB gene as a genuine bacterioferritin (Pa BfrB) [Weeratunga, S. J., et al. (2010) Biochemistry 49, 1160-1175], indicate the coexistence of a bacterial ferritin (Pa FtnA) and a bacterioferritin (Pa BfrB) in P. aeruginosa. In agreement with this idea, we also obtained evidence demonstrating that release of iron from Pa BfrB and Pa FtnA is likely subject to different regulation in P. aerugionsa. Whereas the efficient release of iron stored in Pa FtnA requires only the input of electrons from a ferredoxin NADP reductase (Pa Fpr), the release of iron stored in Pa BfrB requires not only electron delivery by Pa Fpr but also the presence of a "regulator", the apo form of a bacterioferritin-associated ferredoxin (apo Pa Bfd). Finally, structural analysis of iron uptake in crystallo suggests a possible pathway for the internalization of ferroxidase iron into the interior cavity of Pa FtnA.     

Targeting Glioma Stem Cells by Functional Inhibition of a Prosurvival OncomiR-138 in Malignant Gliomas

Malignant gliomas are the most aggressive forms of?brain tumors, associated with high rates of morbidity and mortality. Recurrence and tumorigenesis are attributed to a subpopulation of tumor-initiating glioma stem cells (GSCs) that are intrinsically resistant to therapy. Initiation and progression of gliomas have been linked to alterations in microRNA expression. Here, we report the identification of microRNA-138 (miR-138) as a molecular signature of GSCs and demonstrate a vital role for miR-138 in?promoting growth and survival of bona fide tumor-initiating cells with self-renewal potential. Sequence-specific functional inhibition of miR-138 prevents tumorsphere formation in?vitro and impedes tumorigenesis in?vivo. We delineate the components of the miR-138 regulatory network by loss-of-function analysis to identify specific regulators of apoptosis. Finally, the higher expression of miR-138 in GSCs compared to non-neoplastic tissue and association with tumor recurrence and survival highlights the clinical significance of miR-138 as a prognostic biomarker and a therapeutic target for treatment of malignant gliomas.     

Non-photochemical quenching-dependent acclimation and thylakoid organization of Chlamydomonas reinhardtii to high light stress

Light is essential for all photosynthetic organisms while an excess of it can lead to damage mainly the photosystems of the thylakoid membrane. In this study, we have grown Chlamydomonas reinhardtii cells in different intensities of high light to understand the photosynthetic process with reference to thylakoid membrane organization during its acclimation process. We observed, the cells acclimatized to long-term response to high light intensities of 500 and 1000 µmol m^?2 s^?1 with faster growth and more biomass production when compared to cells at 50 µmol m^?2 s^?1 light intensity. The ratio of Chl a/b was marginally decreased from the mid-log phase of growth at the high light intensity. Increased level of zeaxanthin and LHCSR3 expression was also found which is known to play a key role in non-photochemical quenching (NPQ) mechanism for photoprotection. Changes in photosynthetic parameters were observed such as increased levels of NPQ, marginal change in electron transport rate, and many other changes which demonstrate that cells were acclimatized to high light which is an adaptive mechanism. Surprisingly, PSII core protein contents have marginally reduced when compared to peripherally arranged LHCII in high light-grown cells. Further, we also observed alterations in stromal subunits of PSI and low levels of PsaG, probably due to disruption of PSI assembly and also its association with LHCI. During the process of acclimation, changes in thylakoid organization occurred in high light intensities with reduction of PSII supercomplex formation. This change may be attributed to alteration of protein–pigment complexes which are in agreement with circular dichoism spectra of high light-acclimatized cells, where decrease in the magnitude of psi-type bands indicates changes in ordered arrays of PSII–LHCII supercomplexes. These results specify that acclimation to high light stress through NPQ mechanism by expression of LHCSR3 and also observed changes in thylakoid protein profile/supercomplex formation lead to low photochemical yield and more biomass production in high light condition.

     

H, F-HOESY and PGSE diffusion studies on ionic liquids: The effect of co-solvent on structure

¹H, ¹⁹F-HOESY studies on the ionic liquid based on 1-butyl-3-methylimidazolium tetrafluoroborate, [C₄C₁im]BF₄, [C₄C₁im][N(OTf)₂], and, partially, [C₄C₁im]PF₆, are reported. The addition of methanol separates the ions; however, in dichloromethane solution the anions and cations show strong HOESY contacts even after dilution and taken together with the PGSE diffusion measurements, the data suggest strong ion pairing in this solvent.     

A multiscale framework for defining homeostasis in distal vascular trees: applications to the pulmonary circulation

Biomechanics and Modeling in Mechanobiology - Pulmonary arteries constitute a low-pressure network of vessels, often characterized as a bifurcating tree with heterogeneous vessel mechanics....