Synthesis of novel ligustrazine derivatives as NA+/H+ exchange inhibitors

A novel series of 3,5,6‐trimethylpyrazine‐2‐methoxy (or methylamino) substituted benzoyl‐guanidine derivatives were designed and synthesized as Na⁺/H⁺ exchange (NHE) inhibitors. In this study, compounds with electron‐withdrawing substituents on the benzene ring seemed to improve NHE‐1 inhibitory activities. Compounds 6d, 6k , and 6l were found to be potent inhibitors of NHE‐1 (IC₅₀=3.0±1.6, 3.0±1.4, and 1.6±0.4 nmol/l, resp.). Furthermore, they showed a remarkable reduction of infarct size in the rat myocardial infarction model in vivo.     

Purification and characterization of an active N-acetylglucosaminyltransferase enzyme complex from Streptococci

A new family of bacterial serine-rich repeat glycoproteins can function as adhesins required for biofilm formation and pathogenesis in streptococci and staphylococci. Biogenesis of these proteins depends on a gene cluster coding for glycosyltransferases and accessory secretion proteins. Previous studies show that Fap1, a member of this family from Streptococcus parasanguinis, can be glycosylated by a protein glycosylation complex in a recombinant heterogeneous host. Here we report a tandem affinity purification (TAP) approach used to isolate and study protein complexes from native streptococci. This method demonstrated that a putative glycosyltransferase (Gtf2), which is essential for Fap1 glycosylation, readily copurified with another glycosyltransferase (Gtf1) from native S. parasanguinis. This result and the similar isolation of a homologous two-protein complex from Streptococcus pneumoniae indicate the biological relevance of the complexes to the glycosylation in streptococci. Furthermore, novel N-acetylglucosaminyltransferase activity was discovered for the complexes. Optimal activity required heterodimer formation and appears to represent a novel type of glycosylation.     

Effects of Trp- and Arg-Containing Antimicrobial-Peptide Structure on Inhibition of Escherichia coli Planktonic Growth and Biofilm Formation

Biofilms are sessile microbial communities that cause serious chronic infections with high morbidity and mortality. In order to develop more effective approaches for biofilm control, a series of linear cationic antimicrobial peptides (AMPs) with various arginine (Arg or R) and tryptophan (Trp or W) repeats [(RW)_n-NH₂, where n = 2, 3, or 4] were rigorously compared to correlate their structures with antimicrobial activities affecting the planktonic growth and biofilm formation of Escherichia coli. The chain length of AMPs appears to be important for inhibition of bacterial planktonic growth, since the hexameric and octameric peptides significantly inhibited E. coli growth, while tetrameric peptide did not cause noticeable inhibition. In addition, all AMPs except the tetrameric peptide significantly reduced E. coli biofilm surface coverage and the viability of biofilm cells, when added at inoculation. In addition to inhibition of biofilm formation, significant killing of biofilm cells was observed after a 3-hour treatment of preformed biofilms with hexameric peptide. Interestingly, treatment with the octameric peptide caused significant biofilm dispersion without apparent killing of biofilm cells that remained on the surface; e.g., the surface coverage was reduced by 91.5 ± 3.5% by 200 μM octameric peptide. The detached biofilm cells, however, were effectively killed by this peptide. Overall, these results suggest that hexameric and octameric peptides are potent inhibitors of both bacterial planktonic growth and biofilm formation, while the octameric peptide can also disperse existing biofilms and kill the detached cells. These results are helpful for designing novel biofilm inhibitors and developing more effective therapeutic methods.Antimicrobial peptides (AMPs) are promising alternatives to traditional antibiotics (5). Native AMPs are part of the host defense in organisms ranging from bacteria to insects, plants, and animals (14). They are capable of eliminating a broad spectrum of microorganisms, including viruses, bacteria, and fungi (4, 14). Compared with widespread antibiotic resistance (38), resistance to AMPs is rare, possibly because AMPs directly target cell membranes that are essential to microbes (14, 29). In addition, no cross-resistance has been observed in clinic due to the diversity of peptide sequences (42). Thus, native and synthetic AMPs offer potential alternatives to antibiotics for treating drug-resistant infections (3, 26, 27).In mammalian innate immune systems, some AMPs are produced constitutively, while others are inducible within hours after detection of invading microorganisms (4, 13). Although the detailed mechanism of AMPs'' activities remains elusive (5), AMPs are known to disrupt cell membranes of microbes, interfere with metabolism, and/or target cytoplasmic components (41). Most known AMPs are cationic and amphiphilic (29). It is hypothesized that the initial interaction occurs via an electrostatic attraction between the AMP molecule and microbial membrane. Cationic AMPs can cover bacterial membranes, disrupt the membrane potential, create pores across the membrane, and consequently cause the leak of cell contents and cell death (27, 41). AMPs are relatively selective in targeting microbes rather than mammalian cells, most likely because of the fundamental differences between microbial and host membranes (41), e.g., a higher abundance of negatively charged phospholipids and an absence of cholesterol in microbial membranes.Known AMPs vary dramatically in sequence, size (from 12 to 50 amino acids), and structure (α-helices or β-sheets) (23). However, most AMPs have two types of side chains with relatively conservative sequences: positively charged basic residues, containing arginine (R), lysine (K), and/or histidine (H), that presumably mediate the interaction with the negatively charged microbial membrane, and bulky hydrophobic residues, rich in tryptophan (W), proline (P), and/or phenylalanine (F), that facilitate permeabilization and membrane disruption (26).Although AMPs are promising agents for antimicrobial therapies (15), only a few have made it to clinical trials and applications, with varied success (15, 42). There are several issues that need further development. First, the MICs of AMPs are relatively high compared to those of conventional antibiotics. Recent studies suggest that the peptide/lipid (P/L) ratio needs to be higher than a threshold to allow the AMPs to be oriented perpendicular to the membrane so that pores can be created to kill bacteria (22, 30). Thus, an optimization of peptide structure and size may improve their antimicrobial activities. In addition to the high MICs, the wide application of AMPs is also hindered by their high manufacturing costs and the cytotoxicity of some AMPs.Given the limit of currently available AMPs, it is important to develop more effective AMPs with reduced manufacturing cost and enhanced activity (17, 26, 28, 39). Strøm et al. (39) chemically synthesized a series of short cationic AMPs containing repeating R and W residues in order to identify the minimal pharmacophore with high antimicrobial activities. The data suggest that tetrapeptides or capped tripeptides are effective and there is no correlation between the order of amino acids and antimicrobial activity. Liu et al. (26) analyzed the effects of chain length on the activities of AMPs with repeating pharmacophore sequences (RW)_n-NH₂ (n = 1, 2, 3, 4, or 5). The tests of antimicrobial activities and the hemolysis of red blood cells suggest that (RW)₃-NH₂ has the optimal chain length. Although longer chains are more potent antimicrobials, they can stimulate hemolysis.Most of the AMP studies to date are focused on planktonic bacteria. However, the majority of pathogenic bacteria tend to adhere to surfaces and form sessile microbial communities with highly hydrated structures of secreted polysaccharide matrix, collectively known as biofilms (9). Biofilms can tolerate up to 1,000 times more antibiotics and disinfectants than their planktonic counterparts (2, 7, 8). For example, Folkesson et al. (12) reported that biofilm formation of E. coli K-12 increases its tolerance to polymyxin E, a polypeptide antibiotic that kills Gram-negative bacteria by disrupting membranes (34, 40). Since biofilms are involved in 80% of human bacterial infections (1), it is necessary to study biofilm inhibition and dispersion by AMPs.In this study, a series of linear peptides (RW)_n-NH₂ (where n = 2, 3, or 4) were studied for the effects of their activities on planktonic cells and biofilms of E. coli to understand the structural effects on the antimicrobial activities of AMPs. We chose E. coli RP437 in this study because it is one of the model strains for biofilm research and allows us to compare the data with those of our previous studies (6, 16, 19, 20).     

Optimization of Pulsed-Field Gel Electrophoresis for Legionella pneumophila Subtyping

A total of 32 strains of Legionella pneumophila were used to optimize pulsed-field gel electrophoresis (PFGE) for subtyping of L. pneumophila. Twenty-six isolates of L. pneumophila with various origins and 11 isolates from five different water systems were used as the panels. For optimization of electrophoretic parameters (EPs) of SfiI PFGE, 26 isolates were analyzed with SfiI digestion, using four EPs yielding the same D value. The EP of a switch time of 5 to 50 s for 21 h had the smallest similarity coefficients and was declared the optimal EP for SfiI PFGE of L. pneumophila. By software analysis and pilot study, AscI was chosen as another PFGE enzyme. AscI PFGE could cluster the isolates from each water system into the same or very similar patterns and had a high degree of typing concordance with other molecular methods. In evaluating the discriminatory power of AscI with the panel of 26 isolates, AscI PFGE gave one single pattern and a D value of 100%. AscI PFGE had a high discriminatory power and a high degree of consistency with epidemiological data and other molecular typing methods for L. pneumophila subtyping, and hence, AscI could be used as a restriction enzyme in PFGE subtyping of L. pneumophila.Legionella pneumophila is an environmental organism that can cause disease in humans and is increasingly recognized as an important pathogen causing nosocomial pneumonia. Potable water systems (14, 26), spa water (28), and cooling towers (7, 13) are among the sources implicated in outbreaks of Legionnaires’ disease. Transmission of bacteria from the environment to humans occurs via inhalation or aspiration of Legionella-containing aerosols (3, 5). Strain differentiation is necessary for the identification of sources of contamination and determination of routes of transmission; this could in turn enable us to more accurately detect outbreaks and limit the spread of L. pneumophila infections. A variety of subtyping techniques have been used to identify and characterize L. pneumophila strains, including monoclonal antibody (MAb) analysis (16, 19), ribotyping (4), amplified fragment length polymorphism (AFLP) analysis (9, 22), PCR-based methods (15, 24), sequence-based typing (SBT) (9, 16), and pulsed-field gel electrophoresis (PFGE) (1, 6).Preliminary reports demonstrated that PFGE is a highly discriminative epidemiological marker for subtyping of L. pneumophila (6, 11, 23, 25), and a number of L. pneumophila PFGE protocols have been described in the literature (1, 2, 4, 14); however, most laboratories that use PFGE to subtype L. pneumophila cannot compare their results because the protocols differ from each other in critical parameters, such as the restriction enzymes and electrophoresis conditions used to generate the DNA fingerprints. To enhance our ability to monitor this pathogen, there is an urgent need for a standardized L. pneumophila PFGE protocol which can readily be implemented in different laboratories for information interpretation.An optimal PFGE protocol produces a suitable number of restriction fragments and gives distinct patterns by agarose gel electrophoresis, with these determined by the restriction enzymes and the electrophoretic parameters (EPs) used. SfiI is the most frequently used enzyme in conventional PFGE protocols for L. pneumophila, and there are several different EPs for SfiI digestion used by investigators for characterization and epidemiological studies. For a certain restriction enzyme, selection of the EP with the smallest similarity coefficients will increase the discriminatory power of PFGE. As the first phase of this study, we compared the similarity coefficients obtained for four EPs with SfiI digestion and determined the one with the maximal discriminatory power.There were some problems found in practical applications of epidemiological investigation of L. pneumophila by PFGE with single SfiI digestion, such as having epidemiologically unrelated strains exhibit the same patterns (30) and the appearance of “ghost” or “phantom” bands. Combination use of two enzymes would give a higher discriminatory power and more accurate results (10, 29). Thus, as the second phase of this study, we selected another suitable enzyme and compared it with SfiI to evaluate the possibility of its use in characterization and epidemiological studies of L. pneumophila.     

Geobacillus sp., a Thermophilic Soil Bacterium Producing Volatile Antibiotics

Geobacillus, a bacterial genus, is represented by over 25 species of Gram-positive isolates from various man-made and natural thermophilic areas around the world. An isolate of this genus (M-7) has been acquired from a thermal area near Yellowstone National Park, MT and partially characterized. The cells of this organism are globose (ca. 0.5 μ diameter), and they are covered in a matrix capsule which gives rise to elongate multicelled bacilliform structures (ranging from 3 to 12 μm) as seen by light and atomic force microscopy, respectively. The organism produces unique petal-shaped colonies (undulating margins) on nutrient agar, and it has an optimum pH of 7.0 and an optimum temperature range of 55–65°C. The partial 16S rRNA sequence of this organism has 97% similarity with Geobacillus stearothermophilus, one of its closest relatives genetically. However, uniquely among all members of this genus, Geobacillus sp. (M-7) produces volatile organic substances (VOCs) that possess potent antibiotic activities. Some of the more notable components of the VOCs are benzaldehyde, acetic acid, butanal, 3-methyl-butanoic acid, 2-methyl-butanoic acid, propanoic acid, 2-methyl-, and benzeneacetaldehyde. An exposure of test organisms such as Aspergillus fumigatus, Botrytis cinerea, Verticillium dahliae, and Geotrichum candidum produced total inhibition of growth on a 48-h exposure to Geobacillus sp.(M-7) cells (ca.10⁷) and killing at a 72-h exposure at higher bacterial cell concentrations. A synthetic mixture of those available volatile compounds, at the ratios occurring in Geobacillus sp. (M-7), mimicked the bioactivity of this organism.     

The identity of Ligularia yui (Asteraceae: Senecioneae) from China

Examination of both macro‐ and micro‐morphological characters have shown that Ligularia yui S. W. Liu is conspecific with Senecio spathiphyllus Franch., and is here reduced to a synonym of the latter species.     

Substitution of chloride by bromide modifies the low-temperature tyrosine Z oxidation in active photosystem II

Chloride is an essential cofactor for photosynthetic water oxidation. However, its location and functional roles in active photosystem II are still a matter of debate. We have investigated this issue by studying the effects of Cl⁻ replacement by Br⁻ in active PSII. In Br⁻ substituted samples, Cl⁻ is effectively replaced by Br⁻ in the presence of 1.2 M NaBr under room light with protection of anaerobic atmosphere followed by dialysis. The following results have been obtained. i) The oxygen-evolving activities of the Br⁻-PSII samples are significantly lower than that of the Cl⁻-PSII samples; ii) The same S₂ multiline EPR signals are observed in both Br⁻ and Cl⁻-PSII samples; iii) The amplitudes of the visible light induced S₁Tyr_Z^• and S₂Tyr_Z^• EPR signals are significantly decreased after Br⁻ substitution; the S₁Tyr_Z^• EPR signal is up-shifted about 8 G, whereas the S₂Tyr_Z^• signal is down-shifted about 12 G after Br⁻ substitution. These results imply that the redox properties of Tyr_Z and spin interactions between Tyr_Z^• and Mn-cluster could be significantly modified due to Br⁻ substitution. It is suggested that Cl⁻/Br⁻ probably coordinates to the Ca²⁺ ion of the Mn-cluster in active photosystem II.     

Direct somatic embryogenesis and shoot organogenesis from leaf explants of Primulina tabacum

An efficient propagation system via somatic embryogenesis and shoot organogenesis and plant regeneration system for endangered species Primulina tabacum Hance was established. Thidiazuron (TDZ) was the key plant growth regulator for inducing somatic embryogenesis and kinetin (KIN) and 6-benzylaminopurine (BAP) were the key cytokinins for inducing shoot organogenesis from leaf explants. TDZ combined with BAP or KIN in the induction Murashige and Skoog medium induced both somatic embryos and adventitious shoots. Leaf explants with abaxial site in contact with the medium induced less somatic embryos or adventitious shoots compared to inversely placed leaf explants and the optimum pH was 6.5–7.0. Secondary somatic embryos or adventitious shoot could be induced from primary somatic embryos using TDZ and BAP. Shoots developed adventitious roots on rooting medium containing 0.5 μM indole-3-butyric acid and 0.2 % activated carbon. Over 90 % of plantlets survived following acclimatization and transfer to potting mixture (sand:Vermiculite:limestone; 1:2:1).     

寄生动物

总结归纳了寄生动物的概念和寄生类型,另外对寄生动物适应寄生生活的生物学特性和生活史特征进行了综述。