X-ray crystallographic study of DNA duplex cross-linking: simultaneous binding to two d(CGTACG)(2) molecules by a bis(9-aminoacridine-4-carboxamide) derivative

Acridine-4-carboxamides form a class of known DNA mono-intercalating agents that exhibit cytotoxic activity against tumour cell lines due to their ability to inhibit topoisomerases. Previous studies of bis-acridine derivatives have yielded equivocal results regarding the minimum length of linker necessary between the two acridine chromophores to allow bis-intercalation of duplex DNA. We report here the 1.7 angstrom resolution X-ray crystal structure of a six-carbon-linked bis(acridine-4-carboxamide) ligand bound to d(CGTACG)(2) molecules by non-covalent duplex cross-linking. The asymmetric unit consists of one DNA duplex containing an intercalated acridine-4-carboxamide chromophore at each of the two CG steps. The other half of each ligand is bound to another DNA molecule in a symmetry-related manner, with the alkyl linker threading through the minor grooves. The two crystallographically independent ligand molecules adopt distinct side chain interactions, forming hydrogen bonds to either O6 or N7 on the major groove face of guanine, in contrast to the semi-disordered state of mono-intercalators bound to the same DNA molecule. The complex described here provides the first structural evidence for the non-covalent cross-linking of DNA by a small molecule ligand and suggests a possible explanation for the inconsistent behaviour of six-carbon linked bis-acridines in previous assays of DNA bis-intercalation

End-Tagging of Ultra-Short Antimicrobial Peptides by W/F Stretches to Facilitate Bacterial Killing

BACKGROUND: Due to increasing resistance development among bacteria, antimicrobial peptides (AMPs), are receiving increased attention. Ideally, AMP should display high bactericidal potency, but low toxicity against (human) eukaryotic cells. Additionally, short and proteolytically stable AMPs are desired to maximize bioavailability and therapeutic versatility. METHODOLOGY AND PRINCIPAL FINDINGS: A facile approach is demonstrated for reaching high potency of ultra-short antimicrobal peptides through end-tagging with W and F stretches. Focusing on a peptide derived from kininogen, KNKGKKNGKH (KNK10) and truncations thereof, end-tagging resulted in enhanced bactericidal effect against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Through end-tagging, potency and salt resistance could be maintained down to 4-7 amino acids in the hydrophilic template peptide. Although tagging resulted in increased eukaryotic cell permeabilization at low ionic strength, the latter was insignificant at physiological ionic strength and in the presence of serum. Quantitatively, the most potent peptides investigated displayed bactericidal effects comparable to, or in excess of, that of the benchmark antimicrobial peptide LL-37. The higher bactericidal potency of the tagged peptides correlated to a higher degree of binding to bacteria, and resulting bacterial wall rupture. Analogously, tagging enhanced peptide-induced rupture of liposomes, particularly anionic ones. Additionally, end-tagging facilitated binding to bacterial lipopolysaccharide, both effects probably contributing to the selectivity displayed by these peptides between bacteria and eukaryotic cells. Importantly, W-tagging resulted in peptides with maintained stability against proteolytic degradation by human leukocyte elastase, as well as staphylococcal aureolysin and V8 proteinase. The biological relevance of these findings was demonstrated ex vivo for pig skin infected by S. aureus and E. coli. CONCLUSIONS/SIGNIFICANCE: End-tagging by hydrophobic amino acid stretches may be employed to enhance bactericidal potency also of ultra-short AMPs at maintained limited toxicity. The approach is of general applicability, and facilitates straightforward synthesis of hydrophobically modified AMPs without the need for post-peptide synthesis modifications

Histidine-Rich Glycoprotein Protects from Systemic Candida Infection

Fungi, such as Candida spp., are commonly found on the skin and at mucosal surfaces. Yet, they rarely cause invasive infections in immunocompetent individuals, an observation reflecting the ability of our innate immune system to control potentially invasive microbes found at biological boundaries. Antimicrobial proteins and peptides are becoming increasingly recognized as important effectors of innate immunity. This is illustrated further by the present investigation, demonstrating a novel antifungal role of histidine-rich glycoprotein (HRG), an abundant and multimodular plasma protein. HRG bound to Candida cells, and induced breaks in the cell walls of the organisms. Correspondingly, HRG preferentially lysed ergosterol-containing liposomes but not cholesterol-containing ones, indicating a specificity for fungal versus other types of eukaryotic membranes. Both antifungal and membrane-rupturing activities of HRG were enhanced at low pH, and mapped to the histidine-rich region of the protein. Ex vivo, HRG-containing plasma as well as fibrin clots exerted antifungal effects. In vivo, Hrg−/− mice were susceptible to infection by C. albicans, in contrast to wild-type mice, which were highly resistant to infection. The results demonstrate a key and previously unknown antifungal role of HRG in innate immunity

De l'aspect du temps, représentation et expression du temps passé en anglais et en français (étude contrastive dans une perspective traductologique)

Cette étude est fondamentalement une approche linguistique des problèmes de traduction liés au prétérit et à l imparfait en contexte spécifique. Elle se compose de trois grandes parties. La première s intéresse à la distinction entre aspect lexical et aspect grammatical. Cette distinction se fonde essentiellement sur la définition que donne G. Guillaume de la lexigénèse. La deuxième partie analyse le signifé de puissance de l imparfait et du prétérit ainsi que leurs effets de sens respectifs. Dans la troisième et dernière partie sont introduits quatre concepts clefs visant à justifier la traduction du prétérit simple par l imparfait ou le passé simple, ceux de perfectivité verticale, horizontale, intégrale et transitive. Sont également répertoriés plusieurs critères favorisant l emploi de la forme perfective et imperfective du prétérit, tels que l image temporelle du verbe, le concept philosophique de esse est percipi / percipi est esse, le principe de la deixis ad occulos, etc. Cette étude peut être enfin globalement considérée comme une réflexion sur le principe d orthonymie dans le processus de traduction.This study is basically a linguistic approach to the translation of the English preterite and the French imparfait, primarily in a specific context. It falls into three major parts. The first one focuses on the distinction between lexical and grammatical aspect. This distinction is mainly based on G. Guillaume s definition of the concept of lexigenesis. The second part analyses the potential significate of the imparfait and of the preterit and their related sense effects. In the last and third part, four key concepts are introduced to account for the translation of the simple past into either the imparfait or the passé simple, those of vertical, horizontal, integral and transitive perfectivity. Various criteria are also listed favouring the use of the perfective or the imperfective form of the preterit, such as the temporal contour of the verb, the philosophical concept of esse est percipi / percipi est esse, the deixis ad occulos principle, etc. Lastly, this study can be considered as an overall reflection on the principle of orthonymy underlying the translating process at large.TOULON-BU Centrale (830622101) / SudocSudocFranceF