Browsing by Author "Gonzalez-Nilo, Fernando"
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- ItemBlends containing amphiphilic polymers. V. Compatibilization of N-alkylitaconamic acid-co-styrene copolymers with interacting polymers(2006) Urzúa Acevedo, Marcela del Pilar; Sandoval, Claudia; Gonzalez-Nilo, Fernando; Leiva Campusano, Ángel; Gargallo Gómez, Ligia Teresita; Radić Foschino, Deodato D.
- ItemColloidal nanomedicines with prolonged release of chloroquine based on interactions with aromatic polymers after mixing two liquids: from in silico simulation of nanoparticle formation to efficient in-bench scale up(2024) Villamizar-Sarmiento, Maria Gabriela; Yanez, Osvaldo; Flores, Mario E.; Alvarez-Acevedo, Gonzalo; Gonzalez-Nilo, Fernando; Guerrero, Juan; Moreno-Villoslada, Ignacio; Oyarzun-Ampuero, Felipe A.Nanomedicines containing the aromatic drug chloroquine and the polymer poly(sodium 4-styrenesulfonate) have been theoretically designed and experimentally synthesized following the simple mixture of two aqueous solutions containing the drug and the polymer, respectively. Theoretical calculations show higher binding energy between both the aromatic polymer and chloroquine, and a higher tendency to release water from their hydration spheres, as compared to the binding between the drug and the aliphatic polymer poly(sodium vinyl sulfonate). MD simulations show the spontaneous formation of stable structures of 10 nm of average diameter, even combining short polymer chains, highly diluted reactants, and short reaction time (in the range of mu s). Rapid mixture of the liquids in a stopped flow equipment shows nanoparticle formation in the range of tenths of seconds. Equilibration studies in the range of minutes evidence spheroidal nanoparticles with almost quantitative association efficiency, 48.6 % of drug loading, size of 170 - 410 nm, low polydispersity (PdI = 0.25 - 0.47), and negative zeta potential (-18 - -45 mV). They provide drug release for 30 days, and are stable to NaCl exposure, pH gradient, several temperature values, and long-term storage. Furthermore, we demonstrate scaling up of the nanomedicine production upon increasing the reaction volume. Our studies demonstrate that these highly loaded drug nanoparticles are based on the occurrence of site -specific short-range interactions between the drug and the aromatic excipient such as pi-stacking. In the absence of the aromatic group in the polymer, weak interactions and unstable formulations are evidenced, both theoretically and experimentally. The combination of the selected theoretical and experimental tools could promote the efficient production of drug / polyelectrolyte formulations with therapeutical applications. The chosen components could be considered as potential medicines or as model components to design, develop, characterize, and scale up medicines comprising other combinations of drugs and polymers.
- ItemConformational Changes of Poly(Maleic Anhydride-alt-styrene) Modified with Amino Acids in an Aqueous Medium and Their Effect on Cytocompatibility and Hemolytic Response(2023) Maine, Arianne; Tamayo, Laura; Leiva, Angel; Gonzalez, Alex; Rios, Hernan E.; Rojas-Romo, Carlos; Jara, Paul; Araya-Duran, Ingrid; Gonzalez-Nilo, Fernando; Yazdani-Pedram, Mehrdad; Santana, Paula; Leal, Matias; Gonzalez, Nicolas; Briones, Ximena; Villalobos, Valeria; Urzua, MarcelaThe conformational changes of poly-(maleic anhydride-alt-styrene) (PSMA) modified with different amino acids (PSMA-Aa) were studied in an aqueous medium as a function of ionic strength and pH. The specific viscosity of PSMA-Aa decreased with increasing salt concentration due to a more compact conformation. There was a decrease in surface tension with increasing concentrations of the modified polyelectrolyte having a greater effect for the PSMA modified with l-phenylalanine at pH 7.0, demonstrating a greater surface-active character. The conformational changes were also confirmed by molecular dynamics studies, indicating that PSMA-Aa exhibits a compact structure at pH 4.0 and a more extended structure at pH 7.0. On the other hand, the conformational changes of PSMA-Aa were related to its biological response, where the higher surface-active character of the PSMA modified with l-phenylalanine correlates very well with the higher hemolytic activity observed in red blood cells, in which the surface-active capacity supports lytic potency in erythrocytes. The cytocompatibility assays indicated that there were no significant cytotoxic effects of the PSMA-Aa. Additionally, in solvent-accessible surface area studies, it was shown that the carboxylate groups of the PSMA modified with l-phenylalanine are more exposed to the solvent at pH 7.0 and high salt concentrations, which correlates with lower fluorescence intensity, reflecting a loss of mitochondrial membrane potential. It is concluded that the study of the conformational changes in PE modified with amino acids is essential for their use as biomaterials and relevant to understanding the possible effects of PE modified with amino acids in biological systems.
- ItemDifferent Classes of Antidepressants Inhibit the Rat α7 Nicotinic Acetylcholine Receptor by Interacting within the Ion Channel: A Functional and Structural Study(2021) Duarte, Yorley; Rojas, Maximiliano; Canan, Jonathan; Perez, Edwin G.; Gonzalez-Nilo, Fernando; Garcia-Colunga, JesusSeveral antidepressants inhibit nicotinic acetylcholine receptors (nAChRs) in a non-competitive and voltage-dependent fashion. Here, we asked whether antidepressants with a different structure and pharmacological profile modulate the rat alpha 7 nAChR through a similar mechanism by interacting within the ion-channel. We applied electrophysiological (recording of the ion current elicited by choline, I-Ch, which activates alpha 7 nAChRs from rat CA1 hippocampal interneurons) and in silico approaches (homology modeling of the rat alpha 7 nAChR, molecular docking, molecular dynamics simulations, and binding free energy calculations). The antidepressants inhibited I-Ch with the order: norfluoxetine similar to mirtazapine similar to imipramine < bupropion similar to fluoxetine similar to venlafaxine similar to escitalopram. The constructed homology model of the rat alpha 7 nAChR resulted in the extracellular vestibule and the channel pore is highly negatively charged, which facilitates the permeation of cations and the entrance of the protonated form of antidepressants. Molecular docking and molecular dynamics simulations were carried out within the ion-channel of the alpha 7 nAChR, revealing that the antidepressants adopt poses along the receptor channel, with slightly different binding-free energy values. Furthermore, the inhibition of I-Ch and free energy values for each antidepressant-receptor complex were highly correlated. Thus, the alpha 7 nAChR is negatively modulated by a variety of antidepressants interacting in the ion-channel.
- ItemExcessive release of inorganic polyphosphate by ALS/FTD astrocytes causes non-cell-autonomous toxicity to motoneurons(2022) Arredondo, Cristian; Cefaliello, Carolina; Dyrda, Agnieszka; Jury, Nur; Martinez, Pablo; Diaz, Ivan; Amaro, Armando; Tran, Helene; Morales, Danna; Pertusa, Maria; Stoica, Lorelei; Fritz, Elsa; Corvalan, Daniela; Abarzua, Sebastian; Mendez-Ruette, Maxs; Fernandez, Paola; Rojas, Fabiola; Kumar, Meenakshi Sundaram; Aguilar, Rodrigo; Almeida, Sandra; Weiss, Alexandra; Bustos, Fernando J.; Gonzalez-Nilo, Fernando; Otero, Carolina; Tevy, Maria Florencia; Bosco, Daryl A.; Saez, Juan C.; Kahne, Thilo; Gao, Fen-Biao; Berry, James D.; Nicholson, Katharine; Sena-Esteves, Miguel; Madrid, Rodolfo; Varela, Diego; Montecino, Martin; Brown, Robert H.; van Zundert, BrigitteNon-cell-autonomous mechanisms contribute to neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), in which astrocytes release unidentified factors that are toxic to motoneurons (MNs). We report here that mouse and patient iPSC-derived astrocytes with diverse ALS/FTD-linked mutations (SOD1, TARDBP, and C9ORF72) display elevated levels of intracellular inorganic polyphosphate (polyP), a ubiquitous, negatively charged biopolymer. PolyP levels are also increased in astrocyte-conditioned media (ACM) from ALS/FTD astrocytes. ACM-mediated MN death is prevented by degrading or neutralizing polyP in ALS/FTD astrocytes or ACM. Studies further reveal that postmortem familial and sporadic ALS spinal cord sections display enriched polyP staining signals and that ALS cerebrospinal fluid (CSF) exhibits increased polyP concentrations. Our in vitro results establish excessive astrocyte-derived polyP as a critical factor in non-cell-autonomous MN degeneration and a potential therapeutic target for ALS/ FTD. The CSF data indicate that polyP might serve as a new biomarker for ALS/FTD.
- ItemIn Silico Analysis of Putative Paralytic Shellfish Poisoning Toxins Export Proteins in Cyanobacteria(2013) Soto-Liebe, Katia; Lopez-Cortes, Xaviera A.; Jose Fuentes-Valdes, Juan; Stucken, Karina; Gonzalez-Nilo, Fernando; Vasquez, MonicaParalytic shellfish poisoning toxins (PSTs) are a family of more than 30 natural alkaloids synthesized by dinoflagellates and cyanobacteria whose toxicity in animals is mediated by voltage-gated Na+ channel blocking. The export of PST analogues may be through SxtF and SxtM, two putative MATE (multidrug and toxic compound extrusion) family transporters encoded in PSTs biosynthetic gene cluster (sxt). sxtM is present in every sxt cluster analyzed; however, sxtF is only present in the Cylindrospermopsis-Raphidiopsis clade. These transporters are energetically coupled with an electrochemical gradient of proton (H+) or sodium (Na+) ions across membranes. Because the functional role of PSTs remains unknown and methods for genetic manipulation in PST-producing organisms have not yet been developed, protein structure analyses will allow us to understand their function. By analyzing the sxt cluster of eight PST-producing cyanobacteria, we found no correlation between the presence of sxtF or sxtM and a specific PSTs profile. Phylogenetic analyses of SxtF/M showed a high conservation of SxtF in the Cylindrospermopsis-Raphidiopsis clade, suggesting conserved substrate affinity. Two domains involved in Na+ and drug recognition from NorM proteins (MATE family) of Vibrio parahaemolyticus and V. cholerae are present in SxtF/M. The Na+ recognition domain was conserved in both SxtF/M, indicating that Na+ can maintain the role as a cation anti-transporter. Consensus motifs for toxin binding differed between SxtF and SxtM implying differential substrate binding. Through protein modeling and docking analysis, we found that there is no marked affinity between the recognition domain and a specific PST analogue. This agrees with our previous results of PST export in R. brookii D9, where we observed that the response to Na+ incubation was similar to different analogues. These results reassert the hypothesis regarding the involvement of Na+ in toxin export, as well as the motifs L(398)XGLQD(403) (SxtM) and L(390)VGLRD(395) (SxtF) in toxin recognition.
- ItemSteady State Kinetics for Enzymes with Multiple Binding Sites Upstream of the Catalytic Site(2023) Osorio, Manuel I.; Petrache, Mircea; Salinas, Dino G.; Valenzuela-Ibaceta, Felipe; Gonzalez-Nilo, Fernando; Tiznado, William; Perez-Donoso, Jose M.; Bravo, Denisse; Yanez, OsvaldoThe Michaelis-Menten mechanism, which describes the binding of a substrate to an enzyme, is a simplification of the process on a molecular scale. A more detailed model should include the binding of the substrate to precatalytic binding sites (PCBSs) prior to the transition to the catalytic site. Our work shows that the incorporation of PCBSs, in steady-state conditions, generates a Michaelis-Menten-type expression, in which the kinetic parameters KM and Vmax adopt more complex expressions than in the model without PCBSs. The equations governing reaction kinetics can be seen as generalized symmetries, relative to time translation actions over the state space of the underlying chemical system. The study of their structure and defining parameters can be interpreted as looking for invariants associated with these time evolution actions. The expression of KM decreases as the number of PCBSs increases, while Vmax reaches a minimum when the first PCBSs are incorporated into the model. To evaluate the trend of the dynamic behavior of the system, numerical simulations were performed based on schemes with different numbers of PCBSs and six conditions of kinetic constants. From these simulations, with equal kinetic constants for the formation of the Substrate/PCBS complex, it is observed that KM and Vmax are lower than those obtained with the Michaelis-Menten model. For the model with PCBSs, the Vmax reaches a minimum at one PCBS and that value is maintained for all of the systems evaluated. Since KM decreases with the number of PCBSs, the catalytic efficiency increases for enzymes fitting this model. All of these observations are consistent with the general equation obtained. This study allows us to explain, on the basis of the PCBS to KM and Vmax ratios, the effect on enzyme parameters due to mutations far from the catalytic site, at sites involved in the first enzyme/substrate interaction. In addition, it incorporates a new mechanism of enzyme activity regulation that could be fundamental to search for new activity-modulating sites or for the design of mutants with modified enzyme parameters.
- ItemThe crystal structure of ferritin from Chlorobium tepidum reveals a new conformation of the 4-fold channel for this protein family(2014) Arenas-Salinas, Mauricio; Townsend, Philip D.; Brito, Christian; Marquez, Valeria; Marabolli, Vanessa; Gonzalez-Nilo, Fernando; Matias, Cata; Watt, Richard K.; Lopez-Castro, Juan D.; Dominguez-Vera, Jose; Pohl, Ehmke; Yevenes, AlejandroFerritins are ubiquitous iron-storage proteins found in all kingdoms of life. They share a common architecture made of 24 subunits of five alpha-helices. The recombinant Chlorobium tepidum ferritin (rCtFtn) is a structurally interesting protein since sequence alignments with other ferritins show that this protein has a significantly extended C-terminus, which possesses 12 histidine residues as well as several aspartate and glutamic acid residues that are potential metal ion binding residues. We show that the macromolecular assembly of rCtFtn exhibits a cage-like hollow shell consisting of 24 monomers that are related by 4-3-2 symmetry; similar to the assembly of other ferritins. In all ferritins of known structure the short fifth alpha-helix adopts an acute angle with respect to the four-helix bundle. However, the crystal structure of the rCtFtn presented here shows that this helix adopts a new conformation defining a new assembly of the 4-fold channel of rCtFtn. This conformation allows the arrangement of the C-terminal region into the inner cavity of the protein shell. Furthermore, two Fe(III) ions were found in each ferroxidase center of rCtFtn, with an average FeA-FeB distance of 3 angstrom; corresponding to a diferric mu-oxo/hydroxo species. This is the first ferritin crystal structure with an isolated di-iron center in an iron-storage ferritin. The crystal structure of rCtFtn and the biochemical results presented here, suggests that rCtFtn presents similar biochemical properties reported for other members of this protein family albeit with distinct structural plasticity. (C) 2014 Elsevier B.V. and Societe francaise de biochimie et biologie Moleculaire (SFBBM). All rights reserved.