K(+) versus Na(+) ions in a K channel selectivity filter: a simulation study

Molecular dynamics simulations of a bacterial potassium channel (KcsA) embedded in a phospholipid bilayer reveal significant differences in interactions of the selectivity filter with K(+) compared with Na(+) ions. K(+) ions and water molecules within the filter undergo concerted single-file motion in which they translocate between adjacent sites within the filter on a nanosecond timescale. In contrast, Na(+) ions remain bound to sites within the filter and do not exhibit translocation on a nanosecond timescale. Furthermore, entry of a K(+) ion into the filter from the extracellular mouth is observed, whereas this does not occur for a Na(+) ion. Whereas K(+) ions prefer to sit within a cage of eight oxygen atoms of the filter, Na(+) ions prefer to interact with a ring of four oxygen atoms plus two water molecules. These differences in interactions in the selectivity filter may contribute to the selectivity of KcsA for K(+) ions (in addition to the differences in dehydration energy between K(+) and Na(+)) and the block of KcsA by internal Na(+) ions. In our simulations the selectivity filter exhibits significant flexibility in response to changes in ion/protein interactions, with a somewhat greater distortion induced by Na(+) than by K(+) ions.     

Biocalcification by halophilic bacteria for remediation of concrete structures in marine environment

Microbial carbonate precipitation has emerged as a promising technology for remediation and restoration of concrete structures. Deterioration of reinforced concrete structures in marine environments is a major concern due to chloride-induced corrosion. In the current study, halophilic bacteria Exiguobacterium mexicanum was isolated from sea water and tested for biomineralization potential under different salt stress conditions. The growth, urease and carbonic anhydrase production significantly increased under salt stress conditions. Maximum calcium carbonate precipitation was recorded at 5 % NaCl concentration. Application of E. mexicanum on concrete specimens significantly increased the compressive strength (23.5 %) and reduced water absorption about five times under 5 % salt stress conditions compared to control specimens. SEM and XRD analysis of bacterial-treated concrete specimens confirmed the precipitation of calcite. The present study results support the potential of this technology for improving the strength and durability properties of building structures in marine environments.     

Synthesis of diverse analogues of Oenostacin and their antibacterial activities

Several diverse analogues of Oenostacin, a naturally occurring potent antibacterial phenolic acid derivative, have been synthesized. A small library with more than forty analogues having different aromatic rings and varied side chains has been achieved through solution phase synthesis. Some of these analogues, that is, 22, 23 and 42, possessed potent antibacterial activities against Staphylococcus epidermidis and Staphylococcus aureus having EC(50) ranging from 0.49 to 0.67 microM as compared to Oenostacin (EC(50)=0.12 microM).     

Somatic embryogenesis in Leptadenia reticulata (Retz.) Wight and Arn along with assessment of shoot and callus cultures for HPTLC fingerprint and quantification of p-coumaric acid

Plant Cell, Tissue and Organ Culture (PCTOC) - Leptadenia reticulata (Retz.) Wight and Arn is an important medicinal plant of Asclepiadaceae family. In the present study regeneration was attempted...     

Atropisomerism in Rilpivirine hydrochloride: Spectroscopic characterization of Rilpivirine and related impurities

Nuclear magnetic resonance (NMR) technique has been used to find the property of atropisomerism in Rilpivirine hydrochloride by variable temperature analysis and various 2D techniques. Both the Rilpivirine hydrochloride (E‐isomer) and Impurity‐A (Z‐isomer) isomers have been differentiated and confirmed by NMR and ultraviolet techniques. Preparative high‐performance liquid chromatography isolation for Impurity‐A is followed by spectroscopic (NMR, mass spectra, and infrared) investigation that provides a perfect solution for determination of the structure of Rilpivirine and related impurities.     

Dengue and dengue haemorrhagic fever: implications of host genetics

Little is known of the role of human leucocyte antigen (HLA) alleles or non-HLA alleles in determining resistance, susceptibility or the severity of acute viral infections. Dengue fever (DF) and dengue haemorrhagic fever (DHF) are suitable models for immunogenetic studies, yet only superficial efforts have been made to study dengue disease to date. DF and DHF can be caused by both primary and secondary infection by any of the four serotypes of the dengue virus. Differences in host susceptibility to infectious disease and disease severity cannot be attributed solely to the virus virulence. Variations in immune response, often associated with polymorphism in the human genome, can now be detected. Data on the influence of human genes in DF and DHF are discussed here in relation to (1) associations between HLA polymorphism and dengue disease susceptibility or resistance, (2) protective alleles influencing progression to severe disease, (3) alleles restricting CD4(+) and CD8(+) T lymphocytes, and (4) non-HLA genetic factors that may contribute to DHF evolution. Recent discoveries regarding genetic associations in other viral infections may provide clues to understanding the development of end-stage complications in dengue disease. The scanty positive data presented here indicate a need for detailed genetic studies in different ethnic groups in different countries during the acute phase of DF and DHF on a larger number of patients.