A 500 MHz 2D 1H NMR study of recombinant insect defensin A is reported. This defense protein of 40 residues contains 3 disulfide bridges, is positively charged and exhibits antibacterial properties. ...2D NMR maps of recombinant defensin A were fully assigned and secondary structure elements were localized. The set of NOE connectivities, 3JNH-alpha H coupling constants as well as 1H/2H exchange rates and delta delta/delta T temperature coefficients of NH protons strongly support the existence of an alpha-helix (residues 14-24) and of an antiparallel beta-sheet (residues 27-40). Models of the backbone folding were generated by using the DISMAN program and energy refined by using the AMBER program. This was done on the basis of: (i) 133 selected NOEs, (ii) 21 dihedral restraints from 3JNH-alpha H coupling constants, (iii) 12 hydrogen bonds mostly deduced from 1H/2H exchange rates or temperature coefficients, in addition to 9 initial disulfide bridge covalent constraints. The two secondary structure elements and the two bends connecting them involve approximately 70% of the total number of residues, which impose some stability in the C-terminal part of the molecule. The remaining N-terminal fragment forms a less well defined loop. This spatial organization, in which a beta-sheet is linked to an alpha-helix by two disulfide bridges and to a large loop by a third disulfide bridge, is rather similar to that found in scorpion charybdotoxin and seems to be partly present in several invertebrate toxins.
Diptericins are 9 kDa inducible antibacterial peptides initially isolated from immune heamolymph of Phormia (Diptera). Following the isolation of a Drosophila cDNA encoding a diptericin homologue, we ...have now cloned a genomic fragment containing the Drosophila diptericin gene. To dissect the regulation of this gene, we have transformed flies with a fusion gene in which the reporter beta -galactosidase gene is under the control of 2.2 kb upstream sequences of the diptericin gene. Our analysis reveals at least four distinct phases in the regulation of this gene: young larvae, late third instar larvae, pupae and adults. This complexity may be related to the presence in the upstream sequences of multiple copies of response elements previously characterized in genes encoding acute phase response proteins in mammals (e.g. NK- chi B, NF- chi B related, NF-IL6 response elements).
Thèse de doctorat : Sciences du vivant. Biologie cellulaire et moléculaire : Strasbourg : 2009. Thèse de doctorat : Sciences du vivant. Biologie cellulaire et moléculaire : Boston : 2009.
Thèse ...soutenue sur un ensemble de travaux. Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Bibliogr. 11 p.
Injury or injection of live bacteria into third instar larvae of the dipteran insect Phormia terranovae results in the appearance in the haemolymph of at least five groups of heat-stable, more or ...less basic peptides with antibacterial activity against Escherichia coli . Three of these peptides have been purified. The amino acid sequence has been completely established for one of these and partially (first 40 residues from the N-terminus) for the two others. The authors propose the name of diptercins for this new family of antibiotic molecules.
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