Interception of teicoplanin oxidation intermediates yields new antimicrobial scaffolds

In the search for new efficacious antibiotics, biosynthetic engineering offers attractive opportunities to introduce minor alterations to antibiotic structures that may overcome resistance. Dbv29, a flavin-containing oxidase, catalyzes the four-electron oxidation of a vancomycin-like glycopeptide to yield A40926. Structural and biochemical examination of Dbv29 now provides insights into residues that govern flavinylation and activity, protein conformation and reaction mechanism. In particular, the serendipitous discovery of a reaction intermediate in the crystal structure led us to identify an unexpected opportunity to intercept the normal enzyme mechanism at two different points to create new teicoplanin analogs. Using this method, we synthesized families of antibiotic analogs with amidated and aminated lipid chains, some of which showed marked potency and efficacy against multidrug resistant pathogens. This method offers a new strategy for the development of chemical diversity to combat antibacterial resistance.     

Heat shock protein 90-mediated inactivation of nuclear factor-κB switches autophagy to apoptosis through becn1 transcriptional inhibition in selenite-induced NB4 cells

Autophagy can protect cells while also contributing to cell damage, but the precise interplay between apoptosis and autophagy and the contribution of autophagy to cell death are still not clear. Previous studies have shown that supranutritional doses of sodium selenite promote apoptosis in human leukemia NB4 cells. Here, we report that selenite treatment triggers opposite patterns of autophagy in the NB4, HL60, and Jurkat leukemia cell lines during apoptosis and provide evidence that the suppressive effect of selenite on autophagy in NB4 cells is due to the decreased expression of the chaperone protein Hsp90 (heat shock protein 90), suggesting a novel regulatory function of Hsp90 in apoptosis and autophagy. Excessive or insufficient expression indicates that Hsp90 protects NB4 cells from selenite-induced apoptosis, and selenite-induced decreases in the expression of Hsp90, especially in NB4 cells, inhibit the activities of the IκB kinase/nuclear factor-κB (IKK/NF-κB) signaling pathway, leading to less nuclear translocation and inactivation of NF-κB and the subsequent weak binding of the becn1 promoter, which facilitates the transition from autophagy to apoptosis. Taken together, our observations provide novel insights into the mechanisms underlying the balance between apoptosis and autophagy, and we also identified Hsp90-NF-κB-Beclin1 as a potential biological pathway for signaling the switch from autophagy to apoptosis in selenite-treated NB4 cells.     

Characterization and structural analyses of nonspecific lipid transfer protein 1 from mung bean

Plant nonspecific lipid transfer proteins (nsLTPs) are thermal stable proteins that are capable of transferring lipid molecules between bilayers in vitro. This family of proteins, abundant in plants, is proposed to be involved in defense, pollination, and germination; the in vivo biological function remains, however, elusive. Here we report the purification and sequencing of an nsLTP1 from mung bean sprouts. We have also determined the solution structure of this nsLTP1, which represents the first 3D structure of the dicotyledonous nsLTP1 family. The global fold of mung bean nsLTP1 is similar to those of the monocotyledonous nsLTP1 structures and consists of four alpha-helices stabilized by four disulfide bonds. There are, however, some notable differences in the C-terminal tails and internal hydrophobic cavities. Circular dichroism and fluorescence spectroscopy were used to compare the thermodynamics and lipid transfer properties of mung bean nsLTP1 with those of rice nsLTP1. Docking of a lipid molecule into the solution structure of mung bean nsLTP1 reveals similar binding cavities and hydrophobic interactions as in rice nsLTP1, consistent with their comparable lipid transfer properties measured experimentally.     

农业生态旅游研究进展

在广泛调研现有农业生态旅游研究成果的基础上,从农业生态旅游的概念、特性、国内外研究现状、研究意义和研究方法方面,对农业生态旅游进行了评述。     

Characterization of photodynamic therapy responses elicited in A431 cells containing intracellular organelle‐localized photofrin

Photodynamic therapy (PDT), a photochemotherapeutic regimen used to treat several diseases, including cancer, exerts its effects mainly through induction of cell death. Using human epidermoid carcinoma A431 cells as a model, we previously showed that distinct cell death types could be triggered by protocols that selectively delivered Photofrin (a clinically approved photosensitizer) to different subcellular sites (Hsieh et al. [2003] J Cell Physiol 194: 363–375]. Here, the responses elicited by PDT in A431 cells containing intracellular organelle‐localized Photofrin were further characterized. Two prominent cell phenotypes were observed under these conditions: one characterized by perinuclear vacuole (PV) formation 2–8 h after PDT followed by cell recovery or shrinkage within 48 h, and a second characterized by typical apoptotic features appearing within 4 h after PDT. DCFDA‐sensitive reactive oxygen species formed proximal to PVs during the response to PDT, covering areas in which both endoplasmic reticulum (ER) and the Golgi complex were located. Biochemical analyses showed that Photofrin‐PDT also induced JNK activation and altered the protein secretion profile. A more detailed examination of PV formation revealed that PVs were derived from the ER. The alteration of ER structure induced by PDT was similar to that triggered by thapsigargin, an ER Ca²⁺‐ATPase inhibitor that perturbs Ca²⁺ homeostasis, suggesting a role for Ca²⁺ in the formation of PVs. Microtubule dynamics did not significantly affect PV formation. This study demonstrates that cells in which intracellular organelles are selectively loaded with Photofrin mount a novel response to ER stress induced by PDT. J. Cell. Biochem. 111: 821–833, 2010. © 2010 Wiley‐Liss, Inc.     

Study of cryopreservation of articular chondrocytes using the Taguchi method

This study evaluates the effect of control factors on cryopreservation of articular cartilage chondrocytes using the Taguchi method. Freeze-thaw experiments based on the L₈(2⁷) two-level orthogonal array of the Taguchi method are conducted, and ANOVA (analysis of variables) is adopted to determine the statistically significant control factors that affect the viability of the cell. Results show that the type of cryoprotectant, freezing rate, thawing rate, and concentration of cryoprotectant (listed in the order of influence) are the statistically significant control factors that affect the post-thaw viability. The end temperature and durations of the first and second stages of freezing do not affect the post-thaw viability. Within the ranges of the control factors studied in this work, the optimal test condition is found to be a freezing rate of 0.61 ± 0.03 °C/min, a thawing rate of 126.84 ± 5.57 °C/min, Me₂SO cryoprotectant, and a cryoprotectant concentration of 10% (v/v) for maximum cell viability. In addition, this study also explores the effect of cryopreservation on the expression of type II collagen using immunocytochemical staining and digital image processing. The results show that the ability of cryopreserved chondrocytes to express type II collagen is reduced within the first five days of monolayer culture.     

Mistletoe lectin (Viscum album coloratum) modulates proliferation and cytokine expressions in murine splenocytes

It is well documented that an extract of European mistletoe has a variety of biological effects, such as the stimulation of cytokine production from immune cells, and additional immunoadjuvant activities. While the European mistletoe has been studied intensively, we know less about Korean mistletoe as a therapeutic plant, especially as a possible immunomodulating drug. This study will investigated the effects of Korean mistletoe lectin (Viscum album L. var. coloratum agglutinin, VCA) on murine splenocytes to investigate whether VCA acts as an immunomodulator, which could lead to improved immune responses in these cells. The results showed that VCA inhibited cell proliferation at higher concentrations (at 1-8 ng/ml) and enhanced cell proliferation at lower concentrations (at 4-32 pg/ml). Further studies were carried out to determine if the proproliferative or anti-proliferative activity exhibited by VCA was correlated with cytokine secretion. Consequently, interferon (IFN)-gamma secretion was decreased in concanavalin A (ConA)-stimulated murine splenocytes by VCA (4-64 ng/ml), but there was no change in IL-4 levels. This suggests that VCA has the ability to modulate murine splenocyte proliferation and can possibly act on the balance of Th1/Th2 cellular immune responses.