RESUMEN
The phase equilibria in the MnGa2T?4-MnIn2T?4 system were experimentally investigated by means of differential thermal analysis and powder X-ray diffraction technique. It was found that this system is quasi-binary and characterized by dystectic and eutectic equilibria and the formation of a wide area of solid solutions based on the starting compounds. The crystal structures of the MnGaInTe4 and MnIn2T?4 were refined by the Rietveld method using powder X-ray diffraction data. It was established, that both phases crystallize in the tetragonal system (Space group I-42m). Electron paramagnetic resonance and Raman spectra, as well as the temperature dependences of the electrical conductivity and the Hall effect for the MnGaInTe4 crystal, were studied.
RESUMEN
Phase equilibria in the section Tl4PbTe3-Tl9SmTe6-Tl9BiTe6 of the Tl-Pb-Bi-Sm-Te system were determined by combination of differential thermal analysis, powder X-ray diffraction methods as well as microhardness measurements. The phase diagrams of the boundary systems Tl4PbTe3-Tl9SmTe6, Tl9SmTe6-Tl9BiTe6, isothermal section at 820 and 840 K, some isopleth sections and as well as liquidus and solidus surfaces projections, were plotted. Unlimited solid solutions, which crystallize in Tl5Te3 structure type were found in the system at the solidus temperatures and below.
RESUMEN
Species B human adenoviruses (Ads) are often associated with fatal illnesses in immunocompromised individuals. Recently, species B Ads, most of which use the ubiquitously expressed complement regulatory protein CD46 as a primary attachment receptor, have gained interest for use as gene therapy vectors. In this study, we focused on species B Ad serotype 35 (Ad35), whose trimeric fiber knob domain binds to three CD46 molecules with a KD (equilibrium dissociation constant) of 15.5 nM. To study the Ad35 knob-CD46 interaction, we generated an expression library of Ad35 knobs with random mutations and screened it for CD46 binding. We identified four critical residues (Phe242, Arg279, Ser282, and Glu302) which, when mutated, ablated Ad35 knob binding to CD46 without affecting knob trimerization. The functional importance of the identified residues was validated in surface plasmon resonance and competition binding studies. To model the Ad35 knob-CD46 interaction, we resolved the Ad35 knob structure at 2-A resolution by X-ray crystallography and overlaid it onto the existing structure for Ad11-CD46 interaction. According to our model, all identified Ad35 residues are in regions that interact with CD46, whereby one CD46 molecule binds between two knob monomers. This mode of interaction might have potential consequences for CD46 signaling and intracellular trafficking of Ad35. Our findings are also fundamental for better characterization of species B Ads and design of antiviral drugs, as well as for application of species B Ads as in vivo and in vitro gene transfer vectors.
Asunto(s)
Adenoviridae/metabolismo , Proteínas de la Cápside/genética , Proteínas de la Cápside/metabolismo , Proteína Cofactora de Membrana/metabolismo , Adenoviridae/química , Adenoviridae/clasificación , Adenoviridae/genética , Sustitución de Aminoácidos/genética , Sitios de Unión , Proteínas de la Cápside/química , Cristalografía por Rayos X , Análisis Mutacional de ADN , Humanos , Modelos Moleculares , Mutación Missense , Unión Proteica , Estructura Terciaria de Proteína , Receptores Virales/metabolismo , Resonancia por Plasmón de SuperficieRESUMEN
The Rana catesbeiana (bullfrog) ribonucleases, which belong to the RNase A superfamily, exert cytotoxicity toward tumor cells. RC-RNase, the most active among frog ribonucleases, has a unique base preference for pyrimidine-guanine rather than pyrimidine-adenine in RNase A. Residues of RC-RNase involved in base specificity and catalytic activity were determined by site-directed mutagenesis, k(cat)/K(m) analysis toward dinucleotides, and cleavage site analysis of RNA substrate. The results show that Pyr-1 (N-terminal pyroglutamate), Lys-9, and Asn-38 along with His-10, Lys-35, and His-103 are involved in catalytic activity, whereas Pyr-1, Thr-39, Thr-70, Lys-95, and Glu-97 are involved in base specificity. The cytotoxicity of RC-RNase is correlated, but not proportional to, its catalytic activity. The crystal structure of the RC-RNase.d(ACGA) complex was determined at 1.80 A resolution. Residues Lys-9, His-10, Lys-35, and His-103 interacted directly with catalytic phosphate at the P(1) site, and Lys-9 was stabilized by hydrogen bonds contributed by Pyr-1, Tyr-28, and Asn-38. Thr-70 acts as a hydrogen bond donor for cytosine through Thr-39 and determines B(1) base specificity. Interestingly, Pyr-1 along with Lys-95 and Glu-97 form four hydrogen bonds with guanine at B(2) site and determine B(2) base specificity.