Stereoselectivity in β-cyclodextrin complexation of 1,4-dihydropyridine derivatives

Structure–interaction relationships, stereoselectivity, and solubility enhancement in inclusion compexation of β-cyclodextrins (CDs) with some racemic and enantiomerically pure 1,4-dihydropyridine derivatives (DHPs) were investigated. 1:1 and 1:2 (mole ratio) complexes were prepared and characterized by X-ray powder diffraction, differential scanning calorimetry (DSC), MS-FAB spectrometry, ¹H-NMR spectroscopy, water and phase solubility. The solubility studies have revealed different complexation equilibria for optically pure DHP enantiomers, and corresponding racemic mixtures in water solutions. By means of ¹H-NMR chemical shift measurements, the inclusion of aromatic fragments of racemic and enantiomerically pure DHP molecules within the cavities of different CDs was elucidated. Considerable stereoselectivity in complexation interactions was observed. The results indicate the potential use of cyclodextrins as chiral selectors for enantiomeric resolution of 1,4-DHP calcium antagonists. © 1993 Wiley-Liss, Inc.     

Evolutionary and biogeographical implications of the karyological variations in the oviparous and viviparous forms of the lizard Lacerta (Zootoca) vivipara

The lizard Lacerta ( Zootoca ) vivipara has two modes of reproduction and is variable karyologically. We describe its karyological variation from literature data and from new data on two viviparous populations from France, on two oviparous populations from the Pyrenees in south-western France and on three oviparous populations recently discovered in Slovenia. Males have 36 chromosomes, whereas females have only 35 chromosomes in all viviparous populations and in the Pyrenean oviparous populations. This karyotype has been interpreted to result from a fusion of an ancestral sexual W chromosome with an autosome from the Zl or from the Z2 pair. The karyotype formula is 32 autosomes + ZIZ2W for the female and 32 autosomes + Z1Z1Z2Z2 for the male. The karyotype of the Slovenian oviparous populations, 34 autosomes + ZW in the male and 34 autosomes +ZW in the female, represents an evolutionary stage that preceded the chromosomal fusion. There is minor karyological variation, mainly concerning the W and Z2 chromosomes, within the Pyrenean oviparous populations. This parallels the geographic variation of the W-linked alleles of the MPI enzyme and suggests that allopatric differentiation of these oviparous populations might have occurred in the vicinity of the Pyrenees during the Pleistocene.
The viviparous populations from western Europe carry a metacentric W chromosome, whereas oviparous populations from south-western Europe and eastern viviparous populations both show an acrocentrie, or a subtelocentrie. W chromosome. This suggests that the acrocentric-subtelocentric W is a primitive character and that viviparity probably arose in an eastern lineage of the species.     

Mosquito-only flaviviruses,isolated from <Emphasis Type="Italic">Aedes albopictus</Emphasis> in Slovenia: results of a pilot mosquito monitoring program

Autochthonous transmissions of mosquito-borne diseases were described in close proximity to Slovenia where the knowledge of mosquito species and the viruses they transmit remains very scarce. Therefore we aimed to assess the burden mosquitoes bring to the local community and to test mosquitoes for the presence of the selected zoonotic arboviruses, i. e. Dengue (DENV), West Nile (WNV) and Chikungunya (CHIKV). A pilot mosquito monitoring was conducted in 2012 within two municipalities based on adult mosquito trapping. Altogether 2007 adult mosquitoes were caught. Females of Aedes albopictus and Culex pipiens represented the majority of the total mosquito catch. In sites with more households and nearby greenery, catches of Ae. albopictus were more abundant. Highest numbers of Cx. pipiens females were caught close to a nature reserve, where many bird species stop during their migrations. Trapping results are consistent with both species’ feeding behaviour. Female mosquitoes were grouped into 58 pools according to species, location and date of catch. Real time RT-PCRs for WNV, DENV and CHIKV were performed, but no arboviral genomes were detected in any of the tested mosquito pools. However, amplicons were obtained in three pools when using generic RT-PCR markers for flaviviruses. The viruses detected were propagated and isolated in mosquito cell line C3/36 and identified with sequencing as mosquito-only flaviviruses (MOFs). The important contributions of this study are a successful first isolation of MOFs and confirmation of the presence of the invasive mosquito Ae. albopictus in Slovenia.     

Comparative genomic analysis reveals distinct genotypic features of the emerging pathogen Haemophilus influenzae type f

Background

The incidence of invasive disease caused by encapsulated Haemophilus influenzae type f (Hif) has increased in the post-H. influenzae type b (Hib) vaccine era. We previously annotated the first complete Hif genome from a clinical isolate (KR494) that caused septic shock and necrotizing myositis. Here, the full genome of Hif KR494 was compared to sequenced reference strains Hib 10810, capsule type d (Hid) Rd Kw20, and finally nontypeable H. influenzae 3655. The goal was to identify possible genomic characteristics that may shed light upon the pathogenesis of Hif.

Results

The Hif KR494 genome exhibited large regions of synteny with other H. influenzae, but also distinct genome rearrangements. A predicted Hif core genome of 1390 genes was shared with the reference strains, and 6 unique genomic regions comprising half of the 191 unique coding sequences were revealed. The majority of these regions were inserted genetic fragments, most likely derived from the closely-related Haemophilus spp. including H. aegyptius, H. haemolyticus and H. parainfluenzae. Importantly, the KR494 genome possessed several putative virulence genes that were distinct from non-type f strains. These included the sap2 operon, aef3 fimbriae, and genes for kanamycin nucleotidyltranserase, iron-utilization proteins, and putative YadA-like trimeric autotransporters that may increase the bacterial virulence. Furthermore, Hif KR494 lacked a hisABCDEFGH operon for de novo histidine biosynthesis, hmg locus for lipooligosaccharide biosynthesis and biofilm formation, the Haemophilus antibiotic resistance island and a Haemophilus secondary molybdate transport system. We confirmed the histidine auxotrophy and kanamycin resistance in Hif by functional experiments. Moreover, the pattern of unique or missing genes of Hif KR494 was similar in 20 Hif clinical isolates obtained from different years and geographical areas. A cross-species comparison revealed that the Hif genome shared more characteristics with H. aegyptius than Hid and NTHi.

Conclusions

The genomic comparative analyses facilitated identification of genotypic characteristics that may be related to the specific virulence of Hif. In relation to non-type f H. influenzae strains, the Hif genome contains differences in components involved in metabolism and survival that may contribute to its invasiveness.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-38) contains supplementary material, which is available to authorized users.     

Essential Roles of Hydrophobic Residues in Both MD-2 and Toll-like Receptor 4 in Activation by Endotoxin

Gram-negative bacterial endotoxin (i.e. lipopolysaccharide (LPS)) is one of the most potent stimulants of the innate immune system, recognized by the TLR4·MD-2 complex. Direct binding to MD-2 of LPS and LPS analogues that act as TLR4 agonists or antagonists is well established, but the role of MD-2 and TLR4 in receptor activation is much less clear. We have identified residues within the hairpin of MD-2 between strands five and six that, although not contacting acyl chains of tetraacylated lipid IVa (a TLR4 antagonist), influence activation of TLR4 by hexaacylated lipid A. We show that hydrophobic residues at positions 82, 85, and 87 of MD-2 are essential both for transfer of endotoxin from CD14 to monomeric MD-2 and for TLR4 activation. We also identified a pair of conserved hydrophobic residues (Phe-440 and Phe-463) in leucine-rich repeats 16 and 17 of the TLR4 ectodomain, which are essential for activation of TLR4 by LPS. F440A or F463A mutants of TLR4 were inactive, whereas the F440W mutant retained full activity. Charge reversal of neighboring cationic groups in the TLR4 ectodomain (Lys-388 and Lys-435), in contrast, did not affect cell activation. Our mutagenesis studies are consistent with a molecular model in which Val-82, Met-85, and Leu-87 in MD-2 and distal portions of a secondary acyl chain of hexaacylated lipid A that do not fit into the hydrophobic binding pocket of MD-2 form a hydrophobic surface that interacts with Phe-440 and Phe-463 on a neighboring TLR4·MD-2·LPS complex, driving TLR4 activation.Bacterial lipopolysaccharide (LPS)³ is recognized by the innate immune system of vertebrates via an elaborate mechanism involving the membrane receptor TLR4 (1, 2). The extracellular (or cell surface) proteins LPS-binding protein and CD14 promote extraction and transfer of individual molecules of LPS from the Gram-negative bacterial outer membrane to MD-2, either secreted monomeric soluble (s)MD-2 or MD-2 bound with high affinity to the ectodomain of TLR4 (3–7). In contrast to other Toll-like receptors, TLR4 requires an additional molecule, MD-2, for ligand recognition (8). In contrast to MD-2, there has been no evidence of direct binding of LPS to TLR4 (9, 10). Although LPS, and particularly the lipid A portion of LPS, is generally conserved among Gram-negative bacteria, there are many variables in LPS structure that affect TLR4 activation. Most important is the acylation pattern of the lipid A moiety, which represents the minimal segment of LPS that can trigger activation of TLR4 (11). Comparison of crystal structures of MD-2 with and without bound tetraacylated lipid IVa indicates no significant alteration of the protein fold in the absence or presence of bound ligand (12). It has been proposed that both LPS and MD-2 are key to the different effects of tetra- versus hexaacylated LPS on TLR4 (8, 13, 14). Lipid IVa complexed to murine MD-2 has weak agonist effects on murine TLR4 but acts as a receptor antagonist in the same complex containing human MD-2. Hexaacylated endotoxins complexed to human or murine MD-2 act as potent TLR4 agonists. The crystal structure of the TLR4·MD-2·eritoran complex revealed that MD-2 binds to the N-terminal region of TLR4 (15). It seems likely that for TLR4 activation, there needs to be an additional interaction between two ternary TLR4·MD-2·LPS complexes, which is agonist-dependent (15–17). Because tetraacylated and hexaacylated endotoxins that act, respectively, as TLR4 antagonists and agonists differ only in their acylation pattern, we speculated that hydrophobic protein-lipid A interactions are essential in the agonist properties of hexaacylated lipid A. To pursue this hypothesis, we used molecular modeling to select and test the involvement of solvent-exposed hydrophobic residues of MD-2 and TLR4, which we reasoned could be needed for TLR4 activation. We show by mutagenesis studies that residues on the solvent-exposed hairpin of MD-2 support transfer of endotoxin from CD14 to MD-2 and TLR4 activation only when these sites contain hydrophobic residues. In the ectodomain of TLR4, we have identified two neighboring phenylalanine residues located on the convex face of consecutive leucine rich repeats that are required for LPS-triggered TLR4 activation. From those results and molecular docking, we propose that amino acid side chains of both MD-2 and TLR4 ectodomain form an acyl chain binding site, which envelops part of an acyl chain of lipid A that cannot fit into the binding pocket of MD-2 in a TLR4·MD-2 complex and represents a key to LPS-induced TLR4 activation.     

Influence of temperature and soil water content on bacterial, archaeal and denitrifying microbial communities in drained fen grassland soil microcosms

In this study, microcosms were used to investigate the influence of temperature (4 and 28 degrees C) and water content (45% and 90% WHC) on microbial communities and activities in carbon-rich fen soil. Bacterial, archaeal and denitrifier community composition was assessed during incubation of microcosms for 12 weeks using terminal restriction fragment length polymorphism (T-RFLP) profiling of 16S rRNA and nitrous oxide reductase (nosZ) genes. In addition, microbial and denitrifier abundance, potential denitrification activity and production of greenhouse gases were measured. No detectable changes were observed in prokaryote or denitrifier abundance. In general, cumulatively after 12 weeks more carbon was respired at the higher temperature (3.7 mg CO(2) g(-1) soil), irrespective of the water content, whereas nitrous oxide production was greater under wet conditions (98-336 microg N(2)O g(-1) soil). After an initial lag phase, methane emissions (963 microg CH(4) g(-1) soil) were observed only under warm and wet conditions. T-RFLP analyses of bacterial 16S rRNA and nosZ genes revealed small or undetectable community changes in response to temperature and water content, suggesting that bacterial and denitrifying microbial communities are stable and do not respond significantly to seasonal changes in soil conditions. In contrast, archaeal microbial community structure was more dynamic and was strongly influenced by temperature.     

Taxanes inhibit human TLR4 signaling by binding to MD-2

LPS is the primary ligand of Toll-like receptor 4, activating it through binding to its accessory protein MD-2. Murine but not human cells expressing MD-2/TLR4 are also activated by paclitaxel. Paclitaxel binds to human MD-2. The binding site of paclitaxel overlaps with the binding site of bis-ANS and LPS, which results in the ability of taxanes to inhibit LPS signaling in the system with human receptors. Circular dichroic spectra of human MD-2 indicated differences in the chemical environment in the presence of paclitaxel and docetaxel. Molecular docking identified the interacting residues of MD-2 and suggests that hydrophobic interactions govern the binding, while the C-3′N group where the paclitaxel and docetaxel differ is exposed on the surface of MD-2.     

Variation in eggshell characteristics and in intrauterine egg retention between two oviparous clades of the lizard Lacerta vivipara: insight into the oviparity-viviparity continuum in squamates

The concept of the oviparity-viviparity continuum refers to the wide range in the length of intrauterine egg retention and, hence, in the stage of embryonic development at oviposition existing in squamates. The evolutionary process underlying this continuum may involve not only a lengthening of egg retention in utero, but also a marked reduction in the thickness of the eggshell. The idea that there may exist a negative correlation between the developmental stage reached by the embryo at oviposition and the eggshell thickness within squamates, although supported by the comparison of oviparous vs. viviparous species, has seldom been evaluated by comparing eggshell thickness of oviparous forms with different lengths of intrauterine egg retention. Eggs of two distinct oviparous clades of the lizard Lacerta vivipara were compared. The eggs laid by females from Slovenian and Italian populations have thicker eggshells, contain embryos on average less developed at the time of oviposition, and require a longer incubation period before hatching than the eggs laid by females from French oviparous populations. Our data and several other examples available from the literature support the idea that the lengthening of intrauterine retention of eggs and the shortening of the subsequent external incubation of eggs are associated with reduction in the thickness of the eggshell, at least in some lineages of oviparous squamates. The current hypotheses that may account for this correlation are presented and a few restrictions and refinements to those hypotheses are discussed. In particular, other changes, such as increased vascularization of the oviduct and of the extraembryonic membranes, may play the same role as the decrease of eggshell thickness in facilitating prolonged intrauterine egg retention in squamates. Future studies should also consider the hypothesis that the length of intrauterine retention might directly depend on the extent of maternal-fetal chemical communication through the eggshell barrier.