The aim of the present investigation was to determine whether a plasma membrane high affinity Ca²+-ATPase plays an integral role in the maintenance of cytoplasmic free Ca²+ in pancreatic acinar cells. To achieve this, the Ca²+-transport and Ca²+-ATPase activities were characterized and their properties compared. Plasma membranes from guinea-pig pancreatic acini were shown to contain an ATP-dependent high affinity Ca²+-pump and a high affinity Ca²+-dependent ATPase activity. In addition, a low affinity ATPase activity was also observed. The high affinity Ca²+-ATPase activity as well as the Ca²+-transport were found to be dependent on Mg²+, whereas the low affinity ATPase activity appeared to be inhibited by Mg²+. The high affinity ATPase activity was 7-fold greater in magnitude than the Ca²+-transport. Whereas the Ca²+-transport was very specific for ATP as a substrate, the high affinity Ca²+-ATPase showed little specificity for various nucleotide triphosphates. These data would suggest that the Ca²+-transport and the high affinity Ca²+-dependent ATPase in guinea-pig pancreatic acinar plasma membranes may be two distinct activities To further investigate whether the two activities were related, we investigated how the Ca²+-transport and Ca²+-ATPase activities were regulated by intracellular mediators. Regulation of the two activities by calmodulin, cyclic AMP-dependent protein kinase, Protein kinase C and inositol phosphates was investigated. Calmodulin failed to stimulate either activity. In addition, calmodulin antagonists, trifluoperazine and compound 48/80 produced a concentration-dependent inhibition of Ca²+-transport. These data suggested the presence of endogenous calmodulin. Both antagonists failed to influence the Ca²+-dependent ATPase activity. Experiments using boiled extracts from guinea-pig pancreatic acinar plasma membranes and erythrocyte plasma membranes Ca²+-ATPase confirmed the presence of endogenous calmodulin. The catalytic subunit of cyclic AMP-dependent protein kinase stimulated Ca²+ transport, suggesting that cyclic AMP may have a role in the regulation of Ca²+-pump-mediated Ca²+ efflux from pancreatic acini. Ca²+-dependent ATPase activity, on the other hand, was not affected by the catalytic subunit. HA 1004, a specific inhibitor of cAMP-dependent protein kinase, failed to inhibit the Ca²+-transport and Ca²+-dependent ATPase activities. Since, this inhibitor was also ineffective at inhibiting the catalytic-subunit-stimulated Ca²+ transport, it may be concluded that HA 1004 is ineffective in blocking the actions of cAMP-dependent protein kinase in pancreatic acinar plasma membranes. In our studies, purified protein kinase C, the phorbol ester TPA and the diacylglycerol derivative, SA-DG, failed to stimulate the Ca²+-uptake activity. However, these agents produced stimulation of the Ca²+-dependent ATPase activity in the presence of phosphatidylserine. CGP 41 251, a potent and selective inhibitor of protein kinase C, did not inhibit the Ca²+-transport or Ca²+-dependent ATPase activities. These observations suggest that protein kinase C may not be involved in the regulation of the plasma membrane Ca²+-pump in guinea-pig pancreatic acinar cells. These results also point to another difference between Ca²+-transport and the Ca²+-ATPase activities in guinea-pig pancreatic acinar plasma membranes. Neither inositol trisphosphate nor inositol tetrakisphosphate produced a statistically significant effect on Ca²+-uptake, suggesting that IP₃- and/or IP₄-mediated Ca²+ releasing pathways may not operate in the isolated guinea-pig pancreatic acinar plasma membrane vesicles. In summary, the results presented here provide evidence to suggest that the high affinity Ca²+-ATPase is not the biochemical expression of plasma membrane Ca²+-transport in panreatic acini. Our results imply a role for calmodulin and cAMP-dependent protein kinase, but not protein kinase C, in the regulation of Ca²+ efflux from pancreatic acinar cells. / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate

Orientadores: Francisco Maugeri Filho, Andrea Limoeiro Carvalho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-22T11:19:31Z (GMT). No. of bitstreams: 1 Michelon_Mariano_M.pdf: 21190388 bytes, checksum: 346134051a71b6148d3357e82826c8b8 (MD5) Previous issue date: 2013 / Resumo: Galacto-oligossacarídeos (GOS) são oligossacarídeos não digeríveis que apresentam propriedades prebióticas, pois auxiliam na proliferação de bifidobactérias no cólon. Os GOS podem ser obtidos pela reação de transgalactosilação da galactose catalisada pela enzima ?-galactosidase a partir de substratos ricos em lactose. Neste processo, as misturas de açúcares obtidas após a síntese contêm além dos GOS, mono- e dissacarídeos residuais. Portanto, uma alternativa interessante para aumentar a participação dos GOS no mercado de alimentos funcionais e também incrementar seu valor comercial é sua separação dos demais açúcares. Para tal finalidade, os processos de separação por membranas de nanofiltração podem ser empregados. Estes apresentam vantagens em relação aos processos cromatográficos como a economia de energia e a simplicidade de operação e de ampliação de escala. Deste modo, o objetivo deste trabalho foi desenvolver uma metodologia para purificação de GOS utilizando membranas de nanofiltração. A partir de uma solução modelo contendo GOS, lactose, glicose e galactose, as membranas de nanofiltração NP010 e NP030 constituídas de polietersulfonas com massa molecular de corte de 1000 e 400 Da, respectivamente, e as membranas Desal 5-DK, Desal 5-DL e Desal 5-HL ambas constituídas de poliamidas aromáticas com massa molecular de corte de 150-300 Da foram utilizadas em um sistema de escala laboratorial que simula um processo de filtração tangencial na pressão de 3 MPa a 30°C. A membrana NP030 foi selecionada, pois apresentou nestas condições o maior fator de purificação (FP) de 1,68±0,06, diferindo-se estatisticamente das demais membranas testadas. Após a etapa de seleção, foi conduzido um delineamento composto 22, com faces centradas e tréplicas nos pontos centrais, totalizando 11 ensaios, variando a pressão de operação do sistema (2 a 4 MPa) e a temperatura do processo (15 a 55°C). A pressão de 3 MPa e a temperatura de 35°C resultaram nos maiores valores de FP (>1,77). Em seguida, um processo de diafiltração descontínua foi realizado com a finalidade de aumentar a pureza da solução retida e verificou-se que após a 1º etapa de diafiltração o valor de FP (~1,87) manteve-se constante até o 4º ciclo de diafiltração. As análises das micrografias obtidas através de microscopia eletrônica de varredura (MEV) mostram que a membrana NP030 apresenta deposições de solutos e adesão de micro-organismos na superfície filtrante após sua utilização e lavagem com água, indicando a necessidade de um controle das incrustações e do biofouling para sua reutilização. As micrografias obtidas através de MEV do suporte da membrana indicaram uma possível compactação física. Como etapa subsequente, foi realizada uma validação industrial do processo, utilizando uma unidade piloto de filtração de fluxo tangencial com um módulo espiral da membrana NP030. Foi possível observar que a solução final retida apresentou após 3900 s um valor de FP de 2,55 e uma recuperação de GOS de 97,82%. Foi possível identificar os mecanismos de incrustações dos poros através dos valores dos coeficientes cinéticos de adsorção e pode-se concluir que as incrustações da galactose e da glicose correspondem a um modelo padrão de bloqueio dos poros, enquanto que para os GOS e a lactose a um modelo de bloqueio parcial. Foi estimado o tamanho médio dos poros de permeção da membrana NP030, sendo possível afimar que a probabilidade dos poros de permeação da membrana estarem contidos no intervalo entre 1,94-3,47 nm é de 68,2%. Com estes resultados, pode-se afirmar que as membranas de nanofiltração podem ser utilizadas como uma etapa inicial na purificação dos GOS obtidos através de síntese enzimática. Para obtenção de uma solução com pureza comercial, outras técnicas de purificação deveram ser aplicadas após a nanofiltração / Abstract: Galactooligosaccharides (GOS) are oligosaccharides that present non-digestible prebiotic properties because they assist in the proliferation of bifidobacteria in the human colon. GOS may be obtained by the transgalactosylation reaction of galactose catalyzed by the ?- galactosidase enzyme from substrates rich in lactose. In this process the mixtures of sugars obtained after synthesis contain not only GOS, but also mono-and disaccharide residues. Thus, an interesting alternative to increase the participation of GOS in the functional foods market and also enhance its commercial value is its separation from other sugars. For this purpose, separation processes utilizing nanofiltration membranes may be employed. These processes have advantages over chromatographic processes including energy saving and simplicity of operation and scale increase. The objective of this study was therefore to develop a methodology for purification of GOS using nanofiltration membranes. From a solution containing GOS, lactose, glucose and galactose, the nanofiltration membranes NP010 and NP030, composed of polyethersulfones with molecular weight cut-offs of 1000 Da and 400, respectively, as well as the membranes Desal 5-DK, Desal 5-DL and Desal 5-HL made of aromatic polyamides with molecular mass cut-offs of 150-300 Da were used in a system that simulates a laboratory scale cross-flow filtration process at a pressure of 3 MPa at 30°C. The NP030 membrane was selected because at these conditions it presented the highest purification factor (PF) of 1.68±0.06, statistically different from the other membranes tested. After the selection step, a compound 22 design was conducted with centered faces and triplicate of the central points, totaling 11 assays, varying the operating pressure of the system (2 to 4 MPa) and the process temperature (15 to 55°C). The pressure of 3 MPa and temperature of 35°C resulted in the highest PF values (>1.77). Then a discontinuous diafiltration process was carried out in order to increase the purity of the retained solution, where it was found that after the 1st diafiltration step the PF (~1.87) remained constant until the 4th diafiltration step. Analyses of the micrographs obtained by scanning electron microscopy (SEM) showed that membrane NP030 presents deposits of solutes and adhesion of microorganisms on the filter surface after use and washing with water, indicating the need for control of fouling and biofouling for reuse. The SEM micrographs of the membrane support indicated a possible physical compaction. In a subsequent step, an industrial validation of the process was performed using a pilot tangential flow filtration unit with a model NP030 spiral membrane. It was observed that the final solution retained after 3900 s presented a PF value of 2.55 and a recovery of 97.82% GOS. It was possible to identify the fouling mechanisms of the pores using values of the kinetic adsorption coefficients and it could be concluded that galactose and glucose fouling corresponded to a standard blocking model of the pores, while for lactose and GOS a partial blocking model. The average pore size of the NP030 membrane was estimated, thus it was possible to affirm the probability of the membrane permeation pores in the interval between 1.94-3.47 nm, which was 68.2%. Based on these results, nanofiltration membranes may be used as an initial step in purification of GOS obtained by enzymatic synthesis. To obtain a solution with commercial purity, other purification techniques should be applied after nanofiltration / Mestrado / Engenharia de Alimentos / Mestre em Engenharia de Alimentos

The study of the three-dimensional structures of biological macromolecules has given us significant insight into life and its mechanisms. Understanding these structures in their native contexts, a challenging but important goal, came closer to reality with the development of electron microscopy. After many years of technological development, we are now starting to understand previously intractable biological phenomena at an unprecedented resolution. One such phenomenon is how neighboring cells interact, both to communicate and send signals, and to adhere and form complex tissue structures. While the molecules that mediate such processes have long been studied in isolation, electron microscopy allows us to examine them in a more native biophysical environment; as hydrated, dynamic molecules tethered to opposed cellular membranes.Imaging unadulterated biological material using electron microscopy requires that the sample be embedded in a thin layer of vitreous ice to immobilize the molecules and protect them from the vacuum of the microscope, and thus is generally referred to as cryogenic electron microscopy (cryo-EM). Samples can be imaged using two common cryo-EM modalities: single particle analysis (SPA), where many two-dimensional projection images of molecules in solution are collected, and cryo-electron tomography (cryo-ET), where the sample is tilted as it is imaged at multiple angles to reconstruct a three-dimensional volume. In this work, I will describe how I have used both SPA and cryo-ET to understand cell surface interactions involving a variety of proteins. The first chapter will look at the cell surface molecules known as the Toll receptors, a family of molecules found in Drosophila melanogaster, with orthologs in mammals known as the Toll-like receptors (TLRs). I will focus on their role in the development of the Drosophila embryo during germ band extension, a kind of convergent extension that is a conserved process through all metazoans. Biophysical assays of the three implicated Toll receptors, Toll-2, -6, and -8, revealed both homophilic and heterophilic interactions. SPA was used to determine the structure of monomeric Toll-2 which closely resembles the overall fold of Toll, whose structure was previously solved by x-ray crystallography. Surface plasmon resonance (SPR) spectroscopy and analytical ultracentrifugation (AUC) showed Toll-6 is a dimer in solution, which I visualized using cryo-EM. The Toll-6 homodimer is a novel dimer interface for Tolls and TLRs, where molecules on the same cell surface have been shown to dimerize in the presence of a wide variety of ligands. In contrast, the Toll-6 dimer is formed in the absence of any ligand and exists in an antiparallel arrangement that could be formed by molecules on opposing cell surfaces. Together, these results provide a biochemical basis for germ band extension which may be further explored through the study of structure-based mutations. While cryo-EM SPA is a powerful tool, cryo-ET allows one to reconstruct three dimensional volumes of highly heterogeneous samples, such as the interior of cells, where molecules of interest may not exist in enough copies to facilitate averaging. This technique, where the sample is imaged multiple times as it is tilted to obtain three-dimensional information of a region of interest, was used to study cell adhesion of a different type: that mediated by the classical cadherins. These calcium-dependent adhesion molecules cluster into adherens junctions, spot-like protein densities found in a wide variety of tissues. In the second chapter, these junctions are recapitulated between synthetic liposome membranes by tethering the adherent cadherin molecules to chemically functionalized lipids. They are then imaged using cryo-ET to reveal higher-order structural details. First, this method is applied to the clustered protocadherins, a family of cadherins that mediate neuronal self-avoidance in mammals. Cryo-ET in combination with x-ray crystallography revealed that clustered protocadherins form extended one-dimensional zippers between membranes, which are a combination of strictly homophilic trans interactions coupled with promiscuous cis interactions. Neurons express unique subsets of the ~50-60 possible isoforms, and when two neuronal processes express identical subsets, which happens only when those processes are a part of the same cell, these linear chains grow and initiate a repulsive signal. If the subsets are different, the chains terminate and no repulsive signal is generated. The same technique has been used previously to study the type I classical cadherins, perhaps the most well-studied members of the cadherin superfamily. In the second half of this chapter, we extend our analysis to include the type II classical cadherins, which possess more complex expression patterns and binding specificities. Cryo-ET of type II cadherin ectodomains tethered to synthetic liposomes revealed that several representative members of this family form only moderately ordered arrays between liposomes, a finding in agreement with their role in cell sorting and migration. However, VE-cadherin, an outlier type II expressed in vascular endothelial cells where it withstands blood pressure, forms extraordinarily ordered junctions. Subtomogram averaging reveals the regularity of this two-dimensional array. In the final chapter, I describe my work on a membrane surface molecule of a different kind, one not involved in cell adhesion but viral infection. The global COVID-19 pandemic gave me the opportunity to contribute to our understanding of SARS-CoV-2 by studying the structure of neutralizing antibodies bound to the viral spike protein, perhaps the most infamous membrane surface protein. The first subchapter describes the initial isolation, neutralization, and structural analysis of antibodies isolated from convalescent COVID-19 patients. This work revealed that patients with severe COVID-19 produce potently neutralizing antibodies that target two spike protein domains: the receptor binding domain (RBD) and the N-terminal domain (NTD). RBD-directed antibodies occlude binding to ACE2, the human receptor that mediates viral fusion, but the neutralization mechanism of NTD-directed antibodies is unknown. The following two subchapters are more detailed structural studies of two specific types of antibodies. The first looks at a class of RBD-directed antibodies derived from the VH1-2 gene, which are some of the most potent and common antibodies against SARS-CoV-2. The heavy chains of these antibodies recognize almost identical epitopes, but the antibodies employ a modular approach to recognize the RBD in either of its possible conformations. The second class are antibodies that target the NTD, which our work revealed all bind to a single antigenic supersite. The final subchapter focuses on emerging SARS-CoV-2 variants and includes the structures of two antibodies that are still capable of neutralizing these new variants. They are also infrequent in the human antibody response to SARS-CoV-2, meaning they put little selective pressure on the virus to produce escape mutations, making them good candidates for monoclonal antibody therapies. Though Drosophila embryogenesis, adherens junction formation, and SARS-CoV-2 neutralization are seemingly unrelated systems, they are united by the incredible flexibility of cryo-EM to visualize biological molecules in more native environments. Whether it is the ability to study multiprotein complexes or assemblies formed between membranes, cryo-EM is a powerful technique that promises to help bridge the divide between structure and function.

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / Voltage-gated sodium channels (VGSCs) are dynamic membrane spanning proteins which mediate the rapid influx of Na+ during the upstroke of the action potential (AP). In addition to the large inward Na+ currents responsible for the upstroke of the AP, some VGSC isoforms produce smaller, subthreshold Na+ currents, which can influence the excitable properties of neurons. An example of such a subthreshold current is resurgent Na+ current (INaR). These unusual currents are active during repolarization of the membrane potential, where the channel is normally refractory to activity. INaR exhibit slow gating kinetics and unusual voltage-dependence derived from a novel mechanism of channel inactivation which allows the channel to recover through an open configuration resulting in membrane depolarization early in the falling phase of the AP, ultra-fast re-priming of channels, and multiple AP spikes. Although originally identified in fast spiking central nervous system (CNS) neurons, INaR has recently been observed in a subpopulation of peripheral dorsal root ganglion (DRG) neurons. Because INaR is believed to contribute to spontaneous and high frequency firing of APs, I have hypothesized that increased INaR may contribute to ectopic AP firing associated with inherited and acquired disorders of excitability. Specifically, this dissertation explores the mechanisms which underlie the electrogenesis of INaR in DRG neurons and determines whether the biophysical properties of these unique currents were altered by mutations that cause inherited muscle and neuronal channelopathies or in an experimental model of nerve injury. The results demonstrate that (1) multiple Na+ channel isoforms are capable of producing INaR in DRG neurons, including NaV1.3, NaV1.6, and NaV1.7, (2) inherited muscle and neuronal channelopathIy mutations that slow the rate of channel inactivation increase INaR amplitude, (3) temperature sensitive INaR produced by select skeletal muscle channelopthy mutations may contribute to the triggering of cold-induced myotonia, and (4) INaR amplitude and distribution is significantly increased two weeks post contusive spinal cord injury (SCI). Taken together, results from this dissertation provide foundational knowledge of the properties and mechanism of INaR in DRG neurons and indicates that increased INaR likely contributes to the enhanced membrane excitability associated with multiple inherited and acquired disorders of excitability.

No description available.

No description available.

<p> Calcium (Ca2+) is an important signaling molecule and hence its movement across cell membranes must be tightly regulated. The intracellular Ca2+ concentration ([Ca2+]i) in smooth muscle and endothelium controls the coronary tone. After stimulation, decreasing the [Ca2+]i back to resting levels is achieved mainly by the sodium calcium exchanger (NCX), the plasma membrane calcium pump (PMCA) or the sarcoendoplasmic reticulum calcium pump (SERCA). The present study will focus on NCX and its interactions with SERCA in the smooth muscle and endothelium of pig coronary artery.</p> <p> Aim 1 of my thesis is determination of activity levels of NCX in smooth muscle cells (SMC) and endothelial cells (EC). The NCX activity in cultured cells was approximately 5 times greater in EC than in SMC. The NCX inhibitors KB-R7943 and SEA 0400 blocked the NCX mediated Ca2+ entry, as did collapsing the Na+ gradient with monensin. NCX1 is the isoform largely responsible for NCX activity in SMC and EC. NCX activity was also assayed as the Ca2+ efflux in cultured cells and as Ca2+ uptake in plasma membrane vesicles isolated from freshly isolated smooth muscle.</p> <p> Aim 2 is to assess the existence of a functional NCX mediated Ca2+ entry linked to SERCA in SMC. In the absence of thapsigargin, BAPTA loading SMC increased the NCX mediated uptake. Thapsigargin did not affect the Ca2+ uptake in BAPTA loaded cells but it inhibited the Ca2+ uptake in cells that were not loaded with BAPTA. These data are consistent with a model in which SER acts as a sink for the NCX mediated Ca2+ entry. However, with BAPTA chelation and the resulting lower intracellular Ca2+, the need for SER to act as a sink is eliminated, and NCX is driven in full force. EC did not demonstrate a NCX-SERCA linkage.</p> <p> Arterial SMC and EC differ in their structure and function. The function of SMC is the generation of tone which is achieved by the Ca2+ dependent contractile filaments. Since these filaments are distributed throughout the cell, Ca2+ must be transported to and removed from deep within the cell. As a result, the SER may play a large role in Ca2+ regulation in the SMC. Furthermore, SMC also contain higher levels of high affinity Ca2+ pumps (SERCA and PMCA) and thus Ca2+ is more tightly regulated. Endothelial cells release nitric oxide in response to an increase in [Ca2+]i, which relaxes the smooth muscle. The endothelial nitric oxide sythase produces nitric oxide and is located adjacent to the PM in EC. The SER that removes Ca2+ from deep within the cell cytosol may play a small role in Ca2+ dependent modulation of the endothelial nitric oxide synthase activity. Based on the Western blot data, EC contain a greater amount of the high capacity NCX, thus the larger quantities of Ca2+ can be removed from the cell and the vicinity of endothelial nitric oxide synthase.</p> / Thesis / Master of Science (MSc)

In this paper we study a methodology for the numerical simulation of stable structures of fluid membranes and vesicles in biological organisms. In particular, we discuss the effects of spontaneous curvature on vesicle cell membranes under the bending energy for given volume and surface area. The geometric modeling of the vesicle shapes are undertaken by means of surfaces generated as Partial Differential Equations (PDEs). We combine PDE based geometric modeling with numerical optimization in order to study the stable shapes adopted by the vesicle membranes. Thus, through the PDE method we generate a generic template of a vesicle membrane which is then efficiently parameterized. The parameterization is taken as a basis to set up a numerical optimization procedure which enables us to predict a series of vesicle shapes subject to given surface area and volume.

Em S. cerevisiae, as proteínas de membrana são responsáveis pelo transporte de açúcares através da membrana celular e, portanto, são importantes para os processos fermentativos. Visando melhorar a compreensão do metabolismo de açúcares, estudamos o transporte ativo de açúcares mediado pela permease Agt1p e o processo de inativação catabólica, promovido pela glicose. Para isso, mutantes em resíduos específicos do Agt1p foram gerados por mutagênese e expressados em uma linhagem agt1<font face=\"Symbol\">D. Os resultados obtidos indicam que os aminoácidos Glu-120, Asp-123, Glu-167, Arg-504 e Ile-505 estão envolvidos com o simporte açúcar-H+ realizado pelo Agt1p. Em relação aos resíduos e/ou domínios envolvidos com o processo de inativação catabólica, os resultados demonstram que a região N-terminal do Agt1p, bem como a alça citoplasmática presente entre os TMs 6 e 7, são essenciais para a resposta celular frente a presença de glicose. Finalmente, a fusão do Agt1p com GST permitiu purificar uma proteína de ~67 kDa, condizente com a massa molecular prevista para este transportador. / In S. cerevisiae, membrane proteins are responsible for the transport of different sugars across the cellular membrane and, therefore, are important for fermentation processes. In order to improve our understanding of sugar metabolism, we studied the active sugar transport mediated by Agt1p permease and the catabolite inactivation induced by glucose. Thus, mutants in specific residues of the Agt1p were generated by site direct mutagenesis and expressed in a strain agt1<font face=\"Symbol\">D. The results indicate that the Glu-120, Asp-123, Glu-167, Arg-504 and Ile-505 residues are involved in the sugar-H+ symport mediated by the Agt1p permease. Regarding residues and/or domains involved in the process of catabolite inactivation promoted by glucose, the results indicate that the N-terminal region of Agt1p, and the intracellular loop between TMs 6 and 7, are essential for the cellular response to the presence of glucose. Finally, the fusion of the Agt1p to GST allowed the purification of a ~67 kDa protein, consistent with the predicted molecular weight of this transporter.