Artigos
URI permanente para esta coleçãohttps://locus.ufv.br/handle/123456789/11797
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Item A cooperative transition from the semi-flexible to the flexible regime of polymer elasticity: Mitoxantrone-induced DNA condensation(Biochimica et Biophysica Acta (BBA) - General Subjects, 2018-01-30) Lima, C.H.M.; Almeida, G.O.; Rocha, M.S.We report a high cooperative transition from the semi-flexible to the flexible regime of polymer elasticity during the interaction of the DNA molecule with the chemotherapeutic drug Mitoxantrone (MTX). By using single molecule force spectroscopy, we show that the force-extension curves of the DNA-MTX complexes deviate from the typical worm-like chain behavior as the MTX concentration in the sample increases, becoming straight lines for sufficiently high drug concentrations. The behavior of the radius of gyration of the complexes as a function of the bound MTX concentration was used to quantitatively investigate the cooperativity of the condensation process. The present methodology can be promptly applied to other ligands that condense the DNA molecule upon binding, opening new possibilities in the investigation of this type of process and, more generally, in the investigation of phase transitions in polymer physics.Item Atomic Force Microscopy of spermidine-induced DNA condensates on silicon surfaces(Materials Science and Engineering: C, 2011-09-21) Carrasco, I.S.S.; Bastos, F.M.; Munford, M.L.; Ramos, E.B.; Rocha, M.S.In the present work, we show that oxidized silicon may be successfully used to image multivalent cation-induced DNA condensates under the Atomic Force Microscope (AFM). The images thus obtained are good enough, allowing us to distinguish between different condensate forms and to perform nanometer-sized measurements. Qualitative results previously obtained using mica as a substrate are recovered here. We additionally show that the interactions between the cation spermidine (the condensing agent) and the DNA molecules are not significantly disturbed by the silicon surface, since the phase behavior of an ensemble of DNA molecules deposited on the silicon substrate as a function of the cation concentration is very similar to that found in solution.Item Doxorubicin hinders DNA condensation promoted by the protein bovine serum albumin (BSA)(Biopolymers, 2017-10-23) Lima, C. H. M.; Paula, H. M. C. de; Silva, L. H. M. da; Rocha, M. S.In this work, we have studied the interaction between the anticancer drug doxorubicin (doxo) and condensed DNA, using optical tweezers. To perform this task, we use the protein bovine serum albumin (BSA) in the working buffer to mimic two key conditions present in the real intracellular environment: the condensed state of the DNA and the abundant presence of charged macromolecules in the surrounding medium. In particular, we have found that, when doxo is previously intercalated in disperse DNA, the drug hinders the DNA condensation process upon the addition of BSA in the buffer. On the other hand, when bare DNA is firstly condensed by BSA, doxo is capable to intercalate and to unfold the DNA condensates at relatively high concentrations. In addition, a specific interaction between BSA and doxo was verified, which significantly changes the chemical equilibrium of the DNA–doxo interaction. Finally, the presence of BSA in the buffer stabilizes the double-helix structure of the DNA–doxo complexes, preventing partial DNA denaturation induced by the stretching forces.