Lactam bridge stabilization of α-helical peptides: Ring size,orientation and positional effects

A series of 14 residue amphipathic α-helical peptides, in which the sidechains of glutamic acid and lysine have been covalently joined, was synthesized in order to determine the effect of spacing, position and orientation of these lactam bridges. It was found that although an (i, i+3) spacing would position the lactam bridge on the same face of the helix, these lactams with 18-member rings were actually helix-destabilizing regardless of position or location. On the other hand, (i, i+4) lactams with 21-member rings were helix-stabilizing but this was dependent on orientation. Glutamic acid-lysine lactams increased the helical content of the peptide when compared with their linear homologue in benign conditions (50 mM KH₂PO₄, 100 mM KCl, pH 7). Two Glu-Lys (i, i+4) lactams located at the N- and C-termini gave rise to a peptide with greater than 99% helical content in benign conditions. Peptides with Lys-Glu oriented lactams were random structures in benign conditions but in the presence of 50% TFE could be induced into a helical conformation. The stability of the single-stranded α-helices, as measured by thermal denaturations in 25% TFE indicated that Glu-Lys oriented lactam bridges stabilized the helical conformation relative to the linear unbridged peptide. One Glu-Lys lactam in the middle of the peptide was more effective at stabilizing helical structure than two Glu-Lys lactams positioned one at each end of the molecule. The lactams with the Lys-Glu orientation were destabilizing relative to the unbridged peptide. This study demonstrates that correct orientation and position of a lactam bridge is critical in order to design peptides with high helical content in aqueous media.     

Cytokeratin expression in human respiratory epithelium of nasal polyps and turbinates

The cytokertatins in respiratory epithelial cells (REC) of human nasal polyps and turbinates were analyzed by immunohistochemistry. Cytokeratin 19 (CK19) was present in all REC, CK5 and 14 were expressed primarily in basal cells, and CK7, 8, and 18 were found in suprabasal cells. Differences in cytoplasmic locations were also apparent among the individual cytokeratins. CK13 was not detected in any REC of these tissues. The results indicate the profile of cytokeratins in REC of human nasal polyps and turbinates is essentially identical to that of REC in the more distal respiratory tract.     

Prise en charge psycho-sexologique du patient impuissant

The symptom of impotence is, in the vast majority of cases, extremely welldefined. However, therapeutic approaches incorporate various strategies, including: andrological, analytical and behavioural. A great advance in recent years was due to the development of “integrative models” such as the “American Model” by Helen Kaplan, the “Geneva Model” of Willy Pasini, and our proposed “Parisian Model”, which is founded on the principles of analytical sexotherapy, and comprises several clearly defined stages. The management of impotence must not be restricted only to pharmacological treatment.     

Advantages of the scanning ion microscopy for mapping halogen corticoids in normal and transformed cells in culture

Summary— The intra-cellular distribution of eight halogen glucocorticoids was investigated by ion microscopy in two cellular varieties of cultured non-cancer cells (fibroblast 3T3) and cancer cells (human breast tumor cells MCF-7). Two types of ion microscopy helped to determine this distribution, a direct imaging ion microscope (SMI 300) with low spatial resolution, and a scanning ion microscope (IMS4F), featuring high resolution, serving to obtain maps representing the intra-cellular distribution of the fluorine elements and drugs present in these monolayer cultured cells. The fluorine images representative of the drugs containing fluorine showed that these drugs are essentially concentrated in the cell nuclei. In these nuclei, the distribution of these drugs is different from that of heterochromatin and of the nucleolus.     

Effect of Mate Removal on Current and Subsequent Parental Care in the Convict Cichlid (Pisces: Cichlidae)

In most biparental, substrate-brooding species of cichlid fishes, female and male roles differ. Females are usually more involved in direct care of the young while males spend more time away patrolling the territory. This study tested the flexibility of these sex roles with removal experiments in the convict cichlid, Cichlasoma nigrofasciatum. When males were removed, female fanning activity increased. When females were removed, males spent more time fanning and less time away from the brood. Other behavioural variables (frequency of digging, mouthing, foraging and retrieving) were not affected. Being alone or paired during a first breeding episode did not affect parental behaviour during a subsequent episode in which all fish were paired. Observations were carried out during the day and at night, and nocturnal fanning of fry is reported here for the first time. Female role appears less flexible than male role, as befits the more direct care normally given by females.     

Individual Odors in Djungarian Hamsters (Phodopus campbelli)

The sources of scent in Djungarian hamsters (Phodopus campbelli) that may be individually discriminated were investigated using an habituation paradigm. Male Djungarian hamsters were exposed to five presentations of a particular scent from one individual, and then to the same scent from a novel individual. Increased investigation of the scent from the novel individual indicated discrimination of scents from different individuals. Male hamsters distinguished individual differences in scents of other males from the midventral gland, urine, feces, mouth, and the corner of the mouth, which includes the sacculi; they did not discriminate among odors of different individuals when the scents were from the genital region, hindfeet, fur from behind ears or fur from the back. The results indicate that Djungarian hamsters have a repertoire of individually distinctive scents that are located in specific places on the body; these scents are not actively distributed to, nor passively picked up on, other parts of the body. The fact that scents from some areas do not contain individually distinctive information suggests that some sources may be specialized for producing individually distinctive scents.     

A comparison of the predicted and X-ray structures of angiogenin. Implications for further studies of model building of homologous proteins

The three-dimensional structure of human angiogenin has been determined by X-ray crystallography and is compared here with an earlier model which predicted its structure, based on the homology of angiogenin with bovine pancreatic ribonuclease A. Comparison of the predicted model and crystal structure shows that the active-site histidine residues and the core of the angiogenin molecule, including most of the-strands and-helices, were predicted reasonably well. However, the structure of the surface loop regions and residues near the truncated C-terminus differs significantly. The C-terminal segment includes the active-site residues Asp-116, Gln-117, and Ser-118; Gln-117 in particular has been shown to be important in affecting the ribonucleolytic activity of angiogenin. Also, the orientation of one helix in the model differed from the orientation observed experimentally by about 20°, resulting in a large displacement of this chain segment. The difficulty encountered in predicting the surface loop regions has led to a new algorithm [Palmer and Scheraga (1991),J. Comput. Chem.,12, 505–526; (1992),J. Comput. Chem.,13, 329–350] for predicting the conformations of surface loops.     

Expression of galectins on microvessel endothelial cells and their involvement in tumour cell adhesion

Lactoside-binding lectins (galectins) with molecular weights of about 14.5 kDa (galectin-1) and 29–35 kDa (galectin-3) bind preferentially to polylactosaminoglycan-containing glycoconjugates and have been found on the surface of tumour cells and implicated in cell-cell and cell-extracellular matrix adhesion and metastasis. We have demonstrated by immunoblotting that both galectin-1 and galectin-3 are present in extracts of endothelial cells cultured from bovine aorta, rat lung, mouse lung and mouse brain microvessels, whereas mouse hepatic sinusoidal endothelial cells expressed primarily galectin-1. These galectins were also localized by indirect immunofluorescent labelling on the surface of the different endothelial cells in culture and by immunohistochemical staining in human tissuesin vivo. Anti-galectin-1 antibodies inhibited the adhesion of liver-preferring murine RAW117-H10 large-cell lymphoma cells to hepatic sinusoidal endothelial cells or lung microvessel endothelial cellsin vitro. The data indicate that galectin-1 is expressed on the extracellular surface of endothelial cells and can mediate in part the adhesion of RAW117-H10 cells to liver microvessel endothelial cells.