Repetitive N-WASP–Binding Elements of the Enterohemorrhagic Escherichia coli Effector EspFU Synergistically Activate Actin Assembly

Enterohemorrhagic Escherichia coli (EHEC) generate F-actin–rich adhesion pedestals by delivering effector proteins into mammalian cells. These effectors include the translocated receptor Tir, along with EspFU, a protein that associates indirectly with Tir and contains multiple peptide repeats that stimulate actin polymerization. In vitro, the EspFU repeat region is capable of binding and activating recombinant derivatives of N-WASP, a host actin nucleation-promoting factor. In spite of the identification of these important bacterial and host factors, the underlying mechanisms of how EHEC so potently exploits the native actin assembly machinery have not been clearly defined. Here we show that Tir and EspFU are sufficient for actin pedestal formation in cultured cells. Experimental clustering of Tir-EspFU fusion proteins indicates that the central role of the cytoplasmic portion of Tir is to promote clustering of the repeat region of EspFU. Whereas clustering of a single EspFU repeat is sufficient to bind N-WASP and generate pedestals on cultured cells, multi-repeat EspFU derivatives promote actin assembly more efficiently. Moreover, the EspFU repeats activate a protein complex containing N-WASP and the actin-binding protein WIP in a synergistic fashion in vitro, further suggesting that the repeats cooperate to stimulate actin polymerization in vivo. One explanation for repeat synergy is that simultaneous engagement of multiple N-WASP molecules can enhance its ability to interact with the actin nucleating Arp2/3 complex. These findings define the minimal set of bacterial effectors required for pedestal formation and the elements within those effectors that contribute to actin assembly via N-WASP-Arp2/3–mediated signaling pathways

CHARACTERIZATION OF SURFACE STATES AT A SEMICONDUCTOR ELECTROLYTE INTERFACE BY ELECTROLYTE ELECTROREFLECTANCE SPECTROSCOPY

Les états de surface aux interfaces semiconducteur-liquide sont caractérisés par électroréflectance électrolytique supra- et sub-bande interdite. Les états de surface peuvent se manifester, soit par des transitions optiques directes comme dans le cas de n - TiO2 - électrolyte aqueux, soit par leur effet sur la réponse du niveau de Fermi à de faibles variations du potentiel d'électrode comme dans le cas de monocristaux CdIn2Se4 dans des solutions de polysulfures.Supra bandgap and subband gap Electrolyte Electroreflectance is being used to characterize surface states at semiconductor liquid interfaces. The surface states can manifest themselves either through direct optical transitions as in the case of n - TiO2 - aqueous electrolyte interface or through their effect on the response of the Fermi level to small changes in the electrode potential as in the case of single crystal CdIn2Se4 in polysulfide solutions

Institute of Physics- Sri Lanka Observation of defect interface states at the Cu2O/CuxS junction using thermally stimulated I-V measurements

A simple method was developed to fabricate a Cu 2 O/Cu x S p-n junction diode and I-V characteristics of the diode was measured at various temperatures. It was revealed that there are current transport mechanisms at the junction which are leading to high leakage currents. Namely, an oscillatory behaviour of the current with the temperature was observed under reverse bias conditions. This behaviour was interpreted as the thermally enhanced tunnelling at the junction due to the existence of defect interface states. We believe that proper surface treatment might reduce the density of interface states, and thereby improve the I-V characteristics of the diode. 1

Study of annealing effects of cuprous oxide grown by electrodeposition technique

Low temperature electrochemical deposition of cuprous oxide from aqueous solutions has been investigated. X-ray diffraction, scanning electron microscopy, optical absorption, and photo-response of liquid/cuprous oxide junctions have been used to study the deposits' crystallographic, morphological, optical, and electrical properties. Effects of annealing in air have been studied using the above mentioned methods. As-deposited cuprous oxide exhibits a direct band gap of 2.0 eV, and shows an n-type behaviour when used in an liquid/solid junction. Annealing below 300 degrees C enhances the n-type photocurrent produced by the junction. Type conversion occurs after heat treatments in air at temperatures above 300 degrees C. No apparent bulk structure changes have been observed during annealing below this temperature, but heat treatments above this temperature produce darker films containing cupric oxide and its complexes with water

Electrodeposition and characterisation of CuInSe2 for applications in thin film solar cells

Copper indium diselenide (CuInSe2) layers have been grown at room temperature by electrochemical deposition technique in an aqueous medium. Resulting thin films have been characterised using XRD, XRF, XPS, GDOES and SEM for structural, stoichiometric and morphological properties. A considerable influence of the deposition potential on the atomic composition of In and Se present in the film was observed. Cu composition remains the same within the deposition potentials used in this investigation. The deposited layers are polycrystalline and annealing at 350 degreesC for 30 min improves the crystallinity. The film quality deteriorates due to dissociation when annealed at temperatures above 350 degreesC. Excessive annealing results in a surface which is depleted in Cu and rich in In and Se. (C) 2001 Elsevier Science B.V. All rights reserved

Sulphidation of electrodeposited cuprous oxide thin films for photovoltaic applications

Electrodeposited cuprous oxide thin films on indium-doped tin oxide (ITO) substrates were sulphided by exposing them to a spray of aqueous solution of sodium sulphide or to a mixture of hydrogen sulphide and nitrogen gases. Both methods produced light darker and darker films having different photovoltaic characteristics in a solar cell structure. The photovoltages produced by the light darker films under AM 1.5 illumination was negative as compared to the positive photovoltages produced by the darker films. Spectral response measurements revealed that most of the light darker films produced positive photovoltages in the shorter wavelengths and negative photovoltages in the longer wavelengths. However, Some of the light darker films produced only the negative photovoltage for the entire spectral range and their photovoltaic properties were comparatively better. Darker films resulted in only the positive photovoltages in the entire spectral range. As a result of the sulphidation, the bulk crystal structure of the cuprous oxide thin films was not changed, however, the interfacial characteristics of the solar cell structure were modified. (C) 2000 Elsevier Science B.V. All rights reserved