C and N NMR evidence for peripheral intercalation of uniformly labeled fusogenic peptides incorporated in a biomimetic membrane

Membrane fusion requires drastic and transient changes of bilayer curvature and here we have studied the interaction of three de novo designed synthetic hydrophobic peptides with a biomimetic three-lipid mixture by solid state NMR. An experimental approach is presented for screening of peptide-lipid interactions and their aggregation, and their embedding in a biomimetic membrane system using established proton-decoupled ¹³C, ¹⁵N and proton spin diffusion heteronuclear ¹H−¹³C correlation NMR methods at high magnetic field. Experiments are presented for a set of de-novo designed fusion peptides in interaction with their lipid environment. The data provide additional support for the transmembrane model for the least fusogenic peptide, L16, while the peripheral intercalation model is preferred for the fusogenic peptides LV16 and LV16G8P9. This contributes to converging evidence that peripheral intercalation is both necessary and sufficient to trigger the fusion process for a lipid mixture close to a critical point for phase separation across the bilayer.     

Isolation and Characterization of Dibenzofuran-Degrading <Emphasis Type="Italic">Serratia marcescens</Emphasis> from Alkalophilic Bacterial Consortium of the Chemostat

Alkalophilic bacterial consortium developed by continuous enrichment in the chemostat in presence of 4-chlorosalicylic acid as sole source of carbon and energy contained six bacterial strains, Micrococcus luteus (csa101), Deinococcus radiothilus (csa102), csa103 (Burkholderia gladioli), Alloiococcus otilis (csa104), Micrococcus diversus (csa105), Micrococcus luteus (csa106), identified by the Biolog test method. The strains were tested for utilization of organic compounds in which one of the strains (csa101) had higher potency to utilize dibenzofuran (DF) as sole carbon and energy source identified as Serratia marcescens on the basis of 16S rDNA. The degradation of DF by bacterial strain proceeded through an oxidative route as indicated by 2,2′3-trihydroxybiphenyl, 2-hydroxy-6-(2-hydroxyphenyl)-6-oxo-2,4-hexadienoic acid, salicylic acid, and catechol, which was identified by gas chromatography–mass spectrometry.     

Transgenic mouse lines expressing Cre recombinase specifically in posterior notochord and notochord

During development, the organizer provides instructive signals to surrounding cells as well as contributing cells to axial structures. To dissect organizer function at different developmental stages, conditional approaches such as the Cre/loxP system for conditional mutagenesis are particularly useful. Here we describe two new Cre transgenic mouse lines, Foxa2 NFP-Cre and Nodal PNC-Cre, with activity in two organizer domains, the posterior notochord (PNC) and notochord. These lines were made using defined regulatory elements from the Foxa2 and Nodal genes that direct Cre expression in overlapping domains of the PNC and notochord. Our detailed analysis of the timing and location of Foxa2 NFP-Cre and Nodal PNC-Cre activity indicates that these lines are appropriate for conditional mutagenesis of genes expressed from early somite stages onward.     

The nuclease activities of both the Smr domain and an additional LDLK motif are required for an efficient anti‐recombination function of Helicobacter pylori MutS2

Helicobacter pylori, a human pathogen, is a naturally and constitutively competent bacteria, displaying a high rate of intergenomic recombination. While recombination events are essential for evolution and adaptation of H. pylori to dynamic gastric niches and new hosts, such events should be regulated tightly to maintain genomic integrity. Here, we analyze the role of the nuclease activity of MutS2, a protein that limits recombination during transformation in H. pylori. In previously studied MutS2 proteins, the C‐terminal Smr domain was mapped as the region responsible for its nuclease activity. We report here that deletion of Smr domain does not completely abolish the nuclease activity of HpMutS2. Using bioinformatics analysis and mutagenesis, we identified an additional and novel nuclease motif (LDLK) at the N‐terminus of HpMutS2 unique to Helicobacter and related ε‐proteobacterial species. A single point mutation (D30A) in the LDLK motif and the deletion of Smr domain resulted in ～ 5–10‐fold loss of DNA cleavage ability of HpMutS2. Interestingly, the mutant forms of HpMutS2 wherein the LDLK motif was mutated or the Smr domain was deleted were unable to complement the hyper‐recombination phenotype of a mutS2^? strain, suggesting that both nuclease sites are indispensable for an efficient anti‐recombinase activity of HpMutS2.     

A conserved genetic mechanism specifies deutocerebral appendage identity in insects and arachnids

The segmental architecture of the arthropod head is one of the most controversial topics in the evolutionary developmental biology of arthropods. The deutocerebral (second) segment of the head is putatively homologous across Arthropoda, as inferred from the segmental distribution of the tripartite brain and the absence of Hox gene expression of this anterior-most, appendage-bearing segment. While this homology statement implies a putative common mechanism for differentiation of deutocerebral appendages across arthropods, experimental data for deutocerebral appendage fate specification are limited to winged insects. Mandibulates (hexapods, crustaceans and myriapods) bear a characteristic pair of antennae on the deutocerebral segment, whereas chelicerates (e.g. spiders, scorpions, harvestmen) bear the eponymous chelicerae. In such hexapods as the fruit fly, Drosophila melanogaster, and the cricket, Gryllus bimaculatus, cephalic appendages are differentiated from the thoracic appendages (legs) by the activity of the appendage patterning gene homothorax (hth). Here we show that embryonic RNA interference against hth in the harvestman Phalangium opilio results in homeonotic chelicera-to-leg transformations, and also in some cases pedipalp-to-leg transformations. In more strongly affected embryos, adjacent appendages undergo fusion and/or truncation, and legs display proximal defects, suggesting conservation of additional functions of hth in patterning the antero-posterior and proximo-distal appendage axes. Expression signal of anterior Hox genes labial, proboscipedia and Deformed is diminished, but not absent, in hth RNAi embryos, consistent with results previously obtained with the insect G. bimaculatus. Our results substantiate a deep homology across arthropods of the mechanism whereby cephalic appendages are differentiated from locomotory appendages.     

Priming for enhanced defence responses by specific inhibition of the Arabidopsis response to coronatine

The priming agent β-aminobutyric acid (BABA) is known to enhance Arabidopsis resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst) DC3000 by potentiating salicylic acid (SA) defence signalling, notably PR1 expression. The molecular mechanisms underlying this phenomenon remain unknown. A genome-wide microarray analysis of BABA priming during Pst DC3000 infection revealed direct and primed up-regulation of genes that are responsive to SA, the SA analogue benzothiadiazole and pathogens. In addition, BABA was found to inhibit the Arabidopsis response to the bacterial effector coronatine (COR). COR is known to promote bacterial virulence by inducing the jasmonic acid (JA) response to antagonize SA signalling activation. BABA specifically repressed the JA response induced by COR without affecting other plant JA responses. This repression was largely SA-independent, suggesting that it is not caused by negative cross-talk between SA and JA signalling cascades. Treatment with relatively high concentrations of purified COR counteracted BABA inhibition. Under these conditions, BABA failed to protect Arabidopsis against Pst DC3000. BABA did not induce priming and resistance in plants inoculated with a COR-deficient strain of Pst DC3000 or in the COR-insensitive mutant coi1-16. In addition, BABA blocked the COR-dependent re-opening of stomata during Pst DC3000 infection. Our data suggest that BABA primes for enhanced resistance to Pst DC3000 by interfering with the bacterial suppression of Arabidopsis SA-dependent defences. This study also suggests the existence of a signalling node that distinguishes COR from other JA responses.