RESUMEN
Mn or Co supported CeO2 fiber catalysts were synthesized following a biotemplating route and evaluated in soot combustion and benzene total oxidation. The catalysts were characterized by SEM, EDX, N2 physisorption, FTIR-ATR, XRD, RAMAN and XPS. SEM results confirmed that the "twisted ribbon" morphology of the biotemplate was mostly maintained. XRD and Raman showed that Mn and Co cations partially insert into ceria lattice and also segregate at the surface of the fibers. XPS allowed to determine that both set of catalysts exhibit Ce3+ and Ce4+ species, in addition to adsorbed and lattice oxygen. Also, the average oxidation state (AOS) of surface Mn could be calculated. Compared to bare Fib Ce, the performances for both reactions were improved for the supported catalysts, except from the catalyst with lowest Mn content for soot combustion. The catalytic activity was discussed in terms of the physicochemical features of the supported catalysts.
Asunto(s)
Benceno , Cerio , Cobalto , Manganeso , Oxidación-Reducción , Hollín , Cerio/química , Benceno/química , Catálisis , Manganeso/química , Cobalto/química , Hollín/químicaRESUMEN
Microtubules play an important role in a number of vital cell processes such as cell division, intracellular transport, and cell architecture. The highly dynamic structure of microtubules is tightly regulated by a number of stabilizing and destabilizing microtubule-associated proteins (MAPs), such as tau and stathmin. Because of their importance, tubulin-MAPs interactions have been extensively studied using various methods that provide researchers with complementary but sometimes contradictory thermodynamic data. Isothermal titration calorimetry (ITC) is the only direct thermodynamic method that enables a full thermodynamic characterization (stoichiometry, enthalpy, entropy of binding, and association constant) of the interaction after a single titration experiment. This method has been recently applied to study tubulin-MAPs interactions in order to bring new insights into molecular mechanisms of tubulin regulation. In this chapter, we review the technical specificity of this method and then focus on the use of ITC in the investigation of tubulin-MAPs binding. We describe technical issues which could arise during planning and carrying out the ITC experiments, in particular with fragile proteins such as tubulin. Using examples of stathmin and tau, we demonstrate how ITC can be used to gain major insights into tubulin-MAP interaction.
Asunto(s)
Calorimetría/métodos , Estatmina/metabolismo , Termodinámica , Tubulina (Proteína)/metabolismo , Proteínas tau/metabolismo , Microtúbulos/metabolismo , Unión Proteica , Estatmina/análisis , Tubulina (Proteína)/química , Proteínas tau/análisisRESUMEN
Vinca-alkaloids, such as vinblastine, and some of their derivatives, as for example vinorelbine, are widely used in clinical therapy of leukemia and several types of tumors. Their effects are associated with the disfunctioning of the mitotic spindle, which leads to mitosis blockage and a shutdown of the cell cycle. Their primary target is tubulin, however recent research has shown that some of the vinca-alkaloids inhibit calmodulin binding to its targets. Vinka-alkaloids binding with other proteins could be responsible for their efficiency and neuroprotection. Here we investigated the thermodynamics of vinorelbine interactions with calmodulin and tubulin. It was determined that unlike the other vinca-alkaloids both vinorelbine binding sites are located in the C-domain of calmodulin, and characterized by association constants of 4.0 x 10(5) and 5.4 x 10(4) M(-1). At the same time the thermodynamics of vinorelbine binding to tubulin are not much different from that of other vinca-alkaloids. These results will allow getting a better insight on the reaction mechanisms of vinca-alkaloids on a secondary protein target.
Asunto(s)
Antineoplásicos Fitogénicos/química , Tubulina (Proteína)/metabolismo , Vinblastina/análogos & derivados , Alcaloides de la Vinca/química , Vinca/química , Animales , Calmodulina/química , Ovinos , Termodinámica , Tubulina (Proteína)/química , Vinblastina/química , VinorelbinaRESUMEN
The regulatory protein S100A2 is localized in the cell nucleus and takes part in the regulation of the cell cycle and cancerogenesis. It belongs to a large family of S100 proteins and can simultaneously bind calcium and zinc ions. Using a direct thermodynamical method of isothermal titration calorimetry we have determined that in the absence of calcium ions the S100A2 protein can bind three zinc ions per each monomer. Besides that it was determined that the thermodynamics of zinc binding to different binding sites on the S100A2 are significantly different. Zinc binding to the first two sites on the S100A2 is enthalpically unfavorable and is driven only by entropic factors, while the binding of the third zinc ion is enthalpically favorable. Analysis of the zinc ion adsorption isotherms shows that their binding occurs in a consecutive order.
Asunto(s)
Factores Quimiotácticos/química , Proteínas S100/química , Zinc/química , Factores Quimiotácticos/metabolismo , Humanos , Unión Proteica , Proteínas S100/metabolismo , Termodinámica , Zinc/metabolismoRESUMEN
This review explores various aspects of the interaction between microtubule targeting agents and tubulin, including binding site, affinity, and drug resistance. Starting with the basics of tubulin polymerization and microtubule targeting agent binding, we then highlight how the three-dimensional structures of drug-tubulin complexes obtained on stabilized tubulin are seeded by precise biological and biophysical data. New avenues opened by thermodynamics analysis, high throughput screening, and proteomics for the molecular pharmacology of these drugs are presented. The amount of data generated by biophysical, proteomic and cellular techniques shed more light onto the microtubule-tubulin equilibrium and tubulin-drug interaction. Combining these approaches provides new insight into the mechanism of action of known microtubule interacting agents and rapid in-depth characterization of next generation molecules targeting the interaction between microtubules and associated modulators of their dynamics. This will facilitate the design of improved and/or alternative chemotherapies targeting the microtubule cytoskeleton.
Asunto(s)
Microtúbulos/química , Microtúbulos/metabolismo , Moduladores de Tubulina/química , Antineoplásicos/química , Antineoplásicos/toxicidad , Sitios de Unión , Humanos , Proteómica , Termodinámica , Tubulina (Proteína)/metabolismo , Moduladores de Tubulina/toxicidadRESUMEN
Cryptophycin 52 (C52) is a new synthetic compound of the cryptophycin family of antitumor agents that is currently undergoing clinical evaluation for cancer chemotherapy. The cryptophycin class of compounds acts on microtubules. This report details the mechanism by which C52 substoichiometrically inhibits tubulin self-assembly into microtubules. The inhibition data were analyzed through a model described by Perez-Ramirez [Perez-Ramirez, B., Andreu, J. M., Gorbunoff, M. J., and Timasheff, S. N. (1996) Biochemistry 35, 3277-3285]. We thereby determined the values of the apparent binding constant of the tubulin-C52 complex to the end of a growing microtubule (K(i)) and the apparent binding constant of C52 to tubulin (K(b)). The binding of C52 depended on tubulin concentration, and binding induced changes in the sedimentation pattern of tubulin, which indicates that C52 induces the self-association of tubulin and tubulin aggregates other than microtubules. Using analytical ultracentrifugation and electron microscopy, we show that C52 induces tubulin to form ring-shaped oligomers (single rings). We also show that C52 inhibits the formation of double rings from either GTP- or GDP-tubulin. In addition, the advances made by electron crystallography in understanding the structure of the tubulin and the microtubule allowed us to visualize the putative binding site of C52 and to reconstruct C52-induced ring oligomers by molecular modeling.