Conversion of a disulfide bond into a thioacetal group during echinomycin biosynthesis.

Echinomycin is a nonribosomal depsipeptide natural product with a range of interesting bioactivities that make it an important target for drug discovery and development. It contains a thioacetal bridge, a unique chemical motif derived from the disulfide bond of its precursor antibiotic triostin A by the action of an S-adenosyl-L-methionine-dependent methyltransferase, Ecm18. The crystal structure of Ecm18 in complex with its reaction products S-adenosyl-L-homocysteine and echinomycin was determined at 1.50 Å resolution. Phasing was achieved using a new molecular replacement package called AMPLE, which automatically derives search models from structure predictions based on ab initio protein modelling. Structural analysis indicates that a combination of proximity effects, medium effects, and catalysis by strain drives the unique transformation of the disulfide bond into the thioacetal linkage.

Cinobufagin disrupts the stability of lipid rafts by inhibiting the expression of caveolin-1 to promote non-small cell lung cancer cell apoptosis.

Introduction: The study was designed to explore how cinobufagin (CB) regulates the development of non-small cell lung cancer (NSCLC) cells through lipid rafts. Material and methods: The effects of CB at gradient concentrations (0, 0.5, 1 and 2 µM) on NSCLC cell viability, apoptosis, reactive oxygen species (ROS) level, phosphorylation of Akt, and apoptosis- and lipid raft-related protein expression were assessed by MTT assay, flow cytometry and Western blot. Cholesterol and sphingomyelin were labeled with BODIPY to evaluate the effect of CB (2 µM) on them. Sucrose density gradient centrifugation was used to extract lipid rafts. The effect of CB on the expression and distribution of caveolin-1 was determined by immunofluorescence, quantitative reverse transcription polymerase chain reaction and Western blot. After overexpression of caveolin-1, the above experiments were performed again to observe whether the regulatory effect of CB was reversed. Results: CB inhibited NSCLC cell viability while promoting apoptosis and ROS level. CB redistributed the lipid content on the membrane surface and reduced the content of caveolin-1 in the cell membrane. In addition, CB repressed the activation of AKT. However, caveolin-1 overexpression reversed the effects of CB on apoptosis, AKT activation and lipid raft. Conclusions: CB regulates the activity of Akt in lipid rafts by inhibiting caveolin-1 expression to promote NSCLC cell apoptosis.

Chitinase gene diversity at a deep sea station of the east Pacific nodule province.

The Pacific nodule province covered about 4.5 million km(2) in the east tropical Pacific with an abundance of polymetallic nodules at the seafloor. In view of the environmental protection and resource preservation, the survey of biodiversity was important during the reconnaissance and exploitation in this area. As one of the important component of the deep sea ecosystem, the microbial community in the Pacific nodule province was still largely unknown. The chitinolytic bacteria diversity in deep-sea sediment of a station within the Pacific nodule province was examined by molecular technology. A total of 18 chitinase genes were detected by a set of degenerate PCR primer specific for chiA gene fragment of family 18 chitinase. Most of them belonged to the Serratia-like chitinase. Eight genes had different amino acid sequences in the conserved motif, encompassing the catalytic site among the ChiA protein of family 18 glycosyl hydrolases, and clustered in an independent clade on the phylygenetic tree.