Melectin: a novel antimicrobial peptide from the venom of the cleptoparasitic bee Melecta albifrons

A novel antimicrobial peptide designated melectin was isolated from the venom of the cleptoparasitic bee Melecta albifrons. Its primary sequence was established as H-Gly-Phe-Leu-Ser-Ile-Leu-Lys-Lys-Val-Leu-Pro-Lys-Val-Met-Ala-His-Met-Lys-NH(2) by Edman degradation and ESI-QTOF mass spectrometry. Synthetic melectin exhibited antimicrobial activity against both gram-positive and -negative bacteria and it degranulated rat peritoneal mast cells, but its hemolytic activity was low. The CD spectra of melectin measured in the presence of trifluoroethanol and sodium dodecyl sulfate showed a high content alpha-helices, which indicates that melectin can adopt an amphipathic alpha-helical secondary structure in an anisotropic environment such as the bacterial cell membrane. To envisage the role of the proline residue located in the middle of the peptide chain on biological activity and secondary structure, we prepared several melectin analogues in which the Pro11 residue was either replaced by other amino acid residues or was omitted. The results of biological testing suggest that a Pro kink in the alpha-helical structure of melectin plays an important role in selectivity for bacterial cells. In addition, a series of N- and C-terminal-shortened analogues was synthesized to examine which region of the peptide is related to antimicrobial activity.     

Designing maintainable, reusable interfaces

A conceptual framework, the Interaction Management Network (IMN), that captures the essential structure of any interface from task-oriented specification to object-oriented implementation is presented. IMN is essentially a task-oriented specification scheme based on a semantic network. For each element, as well as for the complete network, there is a direct representation suitable for object-oriented implementation. By capturing task relationships in the interface specification and explicitly representing constraints, designers can create interfaces that meet the often elusive user requirements. The application of IMN to creating an interface system for laying out floors is described     

Xeroderma pigmentosum

MAIN CLINICAL FEATURES: Xeroderma pigmentosum is a rare, recessive disorder clinically characterized by extreme photosensitivity, pigmented abnormalities of the skin-exposed areas, and frequent ocular and neurological abnormalities. Xeroderma pigmentosum syndrome is associated with an estimated 2000-fold increase in the risk to develop skin cancer (basal cell carcinoma, squamous cell carcinoma and melanoma). A HETEROGENEOUS DISEASE: Skin or blood cells from Xeroderma pigmentosum patients are hypersensitive to killing by ultraviolet and hypermutable after ultraviolet C treatment Cell fusion experiments based on complementation of repair synthesis have recognized the presence of seven Xeroderma pigmentosum groups which exhibit various defects in the initial steps of the DNA nucleotide excision repair pathway. A variant Xeroderma pigmentosum form has been found to be normal in nucleotide excision repair but abnormal in a poorly to be normal in nucleotide excision repair but abnormal in a poorly understood postreplication repair process. PATHOPHYSIOLOGY: The Xeroderma pigmentosum complementation groups differ in terms of severity of clinical, cellular and genetic features. Molecular and biochemical studies of the Xeroderma pigmentosum syndrome have led to a better understanding of the mechanisms of ultraviolet-induced sensitivity and the mechanism of cancer development after ultraviolet exposure.     

Surface and Grain Boundary Segregation in Fe‐3%Si Alloy

The surface segregation on the Fe‐3wt.%Si alloy was studied using X‐ray Photoelectron Spectroscopy (XPS) with synchrotron radiation at 150 eV photon beam energy (Si 2p). A silicon oxide layer and also segregation of Si atoms in three clearly resolved phases occurred during heat treatment. A formation of silicides mainly with the Fe₃Si superstructure was observed. A silicon nitride layer was created by nitrogen ion implantation. The structure and atomic ordering in a surface layer of the samples (approx. 300 nm thick) was checked by Conversion Electron Mössbauer Spectroscopy (CEMS). Simultaneously emission Mössbauer spectroscopy was used for the investigation of the Si concentration and atomic ordering at grain boundaries.     

Reversible Formation of Gold Halides in Single‐Crystal Hybrid‐Perovskite/Au Interface upon Biasing and Effect on Electronic Carrier Injection

Solar cells, light emitting diodes, and X‐ray detectors based on perovskite materials often incorporate gold electrodes, either in direct or indirect contact with the perovskite compound. Chemical interactions between active layers and contacts deteriorate the operation and induce degradation, being the identification of the chemical nature of such interfacial structures an open question. Chemical reactivity of gold in contact with the perovskite semiconductor leads to reversible formation of oxidized gold halide species and explains the generation of halide vacancies in the vicinity of the interface. Electrical biasing induces contact reaction and produces modifications of the current level by favoring the ability of perovskite/Au interfaces to inject electronic carriers. The current injection increment does not depend on the halogen source used, either extrinsically by iodine vapor sublimation of Au electrodes, or intrinsically by bias‐driven migration of bromide ions. In addition, the formation of a dipole‐like structure at the reacted electrode that lowers the potential barrier for electronic carriers is confirmed. These findings highlight adequate selection of the external contacts and suggest the need for a deeper understanding of contact reactivity as it dominates the operation characteristics, rather than being governed by the bulk transport properties of the charge carriers, either electronic or ionic.     

Streptomycetes cultured on glass beads: Sample preparation for SEM

We demonstrate the preparation of samples of streptomycetes (Streptomyces coelicolor, S. aureofaciens) cultured on glass beads (balotina) for scanning electron microscopy. The main trick of the method consists in immobilization of glass beads with low-melting agarose. The samples are then fixed in OsO(4) vapors followed by dehydration in vapors of absolute ethanol. No air-to-liquid transition during the sample preparation occurs. Consequently, whole cell cycle of streptomycetes in the term of mycelial morphology can readily be studied by this method.     

Influence of solution properties on the roller electrospinning of poly(vinyl alcohol)

In recent years, nanofiber production via electrospinning has gained importance because of superior properties of submicron fibers. In this study, the effect of molecular weight, concentration of solution, electric conductivity, surface tension and solution viscosity of the polymer solution on the roller electrospinning of PVA nanofibers was investigated. One nonspinnable and two spinnable polymer species were studied. The effect of polymer concentration and solution viscosity on the electrospinning process throughput, fiber diameters and quality of nanofiber layers was measured. According to the results there is a significant difference in rheological behavior of nonspinnable and spinnable polymer solutions. Electric conductivity and surface tension of the solutions did not influence both throughput and fiber diameter significantly. Whereas molecular weight has an important effect on the spinnability, concentration of the solutions has not. On the contrary, concentration influences the process throughput considerably and properties of nanofibers and nanofiber layers to some extent. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Bordetella adenylate cyclase toxin induces a cascade of morphological changes of sheep erythrocytes and localizes into clusters in erythrocyte membranes

Adenylate cyclase toxin (CyaA) of Bordetella pertussis penetrates the membrane of eukaryotic cells, producing high levels of intracellular cAMP, as well as hemolysis that results from the formation of cation-selective toxin channels in the membrane. Using several microscopical approaches we studied the effects of CyaA action on the morphology of sheep erythrocytes during early phases preceding lysis and examined localization of CyaA molecules within the erythrocyte membrane. CyaA induced a cascade of morphological changes of erythrocytes, such as shrinkage, formation of membrane projections, and blebs and swelling. The use of an enzymatically inactive CyaA-AC- toxoid that is unable to produce cAMP and of a CyaA-E581K mutant exhibiting higher hemolytic activity than with CyaA showed that the hemolytic activity is responsible for the induction of morphological changes of erythrocytes. Further, immunolabeling of inserted CyaA-232/FLAG molecules with specific anti-FLAG antibodies and IgG-gold particles indicated a clustered distribution of CyaA molecules in erythrocyte membrane. This was confirmed by immunofluorescence and confocal microscopy, which revealed uniform stoichiometry of CyaA clusters, suggesting CyaA binding into specific domains in erythrocyte membrane. Indeed, a decrease of CyaA binding after cholesterol depletion of erythrocytes suggests toxin targeting and binding to membrane microdomains (rafts).