A Na,K-ATPase é uma proteína integral que utiliza a energia derivada da hidrólise do ATP para transportar íons Na+ e K+ através da membrana contra seus gradientes eletroquímicos. É composta por três subunidades, denominadas alfa, beta e gama. Alguns autores defendem que o protômero (alfa-beta) seja a unidade estrutural e funcional da enzima, porém outros consideram que a enzima nativa da membrana funciona como um oligômero, na forma de um dímero (alfa-beta)2. Em estudos com proteínas de membrana, o uso de detergentes é bastante comum para manter a proteína de interesse em um estado funcional após ser retirada da bicamada lipídica, além disso, sabe-se que vários fatores interferem a atividade enzimática da Na,K-ATPase e existem evidências que mostram que a bicamada lipídica, na qual a enzima está inserida, também controla a interação entre os protômeros da proteína e alterações nas suas propriedades biofísicas podem modular a atividade da enzima. O objetivo do trabalho foi verificar o efeito de diferentes razões detergente/proteína na estabilidade da Na,K-ATPase solubilizada e de diferentes microambientes lipídicos na sua atividade, analisando as alterações no comportamento termotrópico da bicamada com a mudança da composição lipídica, observando as alterações da incorporação e recuperação da atividade enzimática quando a proteína foi reconstituída em sistemas miméticos de membrana. Utilizando o espalhamento dinâmico de luz (DLS) foi possível acompanhar o processo de agregação térmica da enzima, fornecendo informações da sua estrutura, bem como avaliar a sua estabilidade quando solubilizada. A desnaturação térmica da Na,K-ATPase também foi avaliada por calorimetria diferencial de varredura (DSC) e verificou-se que é um processo irreversível, e ocorreu entre 50 e 70°C, sendo a soma de três transições. Utilizando DSC, analisou-se ainda o comportamento termotrópico dos sistemas de lipossomos e proteolipossomos constituídos de DPPC, DPPE e colesterol. Para os sistemas vesiculares, na ausência da proteína, foi observado que para o sistema binário de DPPC e DPPE, o aumento da proporção do último lipídio induz uma separação de fase, assim como a presença de colesterol, tanto nos sistemas binários (DPPC:Col e DPPE:Col), quanto no ternário (DPPC:DPPE:Col). Avaliou-se ainda como o microambiente lipídico interfere na incorporação e atividade da Na,K-ATPase. Verificou que diferentes quantidades de colesterol alteram a atividade enzimática, confirmando que este possui um importante papel na modulação da atividade, alterando propriedades da membrana e influenciando na conformação da proteína. / Na,K-ATPase is an enzyme that is intrinsic to the plasma membrane, responsible for the coupled active transport of Na+ and K+ across animal cell membranes. The enzyme consists of alfa, beta and gama subunits. It has been demonstrated that the alfa-beta form of Na,K-ATPase is capable of both ATP hydrolysis and active ion transport, however accumulating evidence suggest that the enzyme normally self-associates as (alfa-beta)2 dimers. In membrane protein research, the most typical use of a detergent is to maintain a target membrane protein in a functional, folded state in the absence of a membrane. Moreover, it is known that several factors influence the enzymatic activity of Na, K-ATPase and there is evidence that the lipid bilayer, in which the enzyme is located, also controls the interaction between protomers and that changes in their biophysical properties can modulate the activity of the enzyme. The objective of this study was to investigate the effect of different detergent/protein ratios on the stability solubilized of Na, K-ATPase and different lipid microenvironments in their activity by analyzing changes in the thermotropic behavior of the bilayer, analysing the incorporation changes and the recovery of enzyme activity when the protein was reconstituted in a membrane mimetic systems. Dynamic light scattering (DLS) was used to monitor the process of thermal aggregation of the enzyme, providing information on their structure and evaluating its stability when solubized. The thermal denaturation of Na, K-ATPase was also evaluated by differential scanning calorimetry (DSC) and it was verified that it is an irreversible process, which occurred between 50 and 70 ° C, being the sum of three transitions. Using DSC, we analyzed the thermotropic behavior of proteolipossomos and liposomes consisting of DPPC, DPPE and cholesterol. For vesicular systems in the absence of the protein, it was observed that for the binary system of DPPC and DPPE, increasing the proportion of the latter induces a lipid phase separation and the presence of cholesterol in both binary systems (DPPC: Col and DPPE: Chol), and in the ternary system (DPPC: DPPE: Chol) it induces a lipid phase separation. It was also evaluated how the lipid microenvironment interferes on the incorporation and activity of Na, K-ATPase. It was found that different amounts of cholesterol alter the enzyme activity, confirming cholesterol has an important role in the modulation of the activity by altering the membrane properties and influencing the protein conformation.

A Na,K-ATPase é uma proteína integral que utiliza a energia derivada da hidrólise do ATP para transportar íons Na+ e K+ através da membrana contra seus gradientes eletroquímicos. É composta por três subunidades, denominadas alfa, beta e gama. Alguns autores defendem que o protômero (alfa-beta) seja a unidade estrutural e funcional da enzima, porém outros consideram que a enzima nativa da membrana funciona como um oligômero, na forma de um dímero (alfa-beta)2. Em estudos com proteínas de membrana, o uso de detergentes é bastante comum para manter a proteína de interesse em um estado funcional após ser retirada da bicamada lipídica, além disso, sabe-se que vários fatores interferem a atividade enzimática da Na,K-ATPase e existem evidências que mostram que a bicamada lipídica, na qual a enzima está inserida, também controla a interação entre os protômeros da proteína e alterações nas suas propriedades biofísicas podem modular a atividade da enzima. O objetivo do trabalho foi verificar o efeito de diferentes razões detergente/proteína na estabilidade da Na,K-ATPase solubilizada e de diferentes microambientes lipídicos na sua atividade, analisando as alterações no comportamento termotrópico da bicamada com a mudança da composição lipídica, observando as alterações da incorporação e recuperação da atividade enzimática quando a proteína foi reconstituída em sistemas miméticos de membrana. Utilizando o espalhamento dinâmico de luz (DLS) foi possível acompanhar o processo de agregação térmica da enzima, fornecendo informações da sua estrutura, bem como avaliar a sua estabilidade quando solubilizada. A desnaturação térmica da Na,K-ATPase também foi avaliada por calorimetria diferencial de varredura (DSC) e verificou-se que é um processo irreversível, e ocorreu entre 50 e 70°C, sendo a soma de três transições. Utilizando DSC, analisou-se ainda o comportamento termotrópico dos sistemas de lipossomos e proteolipossomos constituídos de DPPC, DPPE e colesterol. Para os sistemas vesiculares, na ausência da proteína, foi observado que para o sistema binário de DPPC e DPPE, o aumento da proporção do último lipídio induz uma separação de fase, assim como a presença de colesterol, tanto nos sistemas binários (DPPC:Col e DPPE:Col), quanto no ternário (DPPC:DPPE:Col). Avaliou-se ainda como o microambiente lipídico interfere na incorporação e atividade da Na,K-ATPase. Verificou que diferentes quantidades de colesterol alteram a atividade enzimática, confirmando que este possui um importante papel na modulação da atividade, alterando propriedades da membrana e influenciando na conformação da proteína. / Na,K-ATPase is an enzyme that is intrinsic to the plasma membrane, responsible for the coupled active transport of Na+ and K+ across animal cell membranes. The enzyme consists of alfa, beta and gama subunits. It has been demonstrated that the alfa-beta form of Na,K-ATPase is capable of both ATP hydrolysis and active ion transport, however accumulating evidence suggest that the enzyme normally self-associates as (alfa-beta)2 dimers. In membrane protein research, the most typical use of a detergent is to maintain a target membrane protein in a functional, folded state in the absence of a membrane. Moreover, it is known that several factors influence the enzymatic activity of Na, K-ATPase and there is evidence that the lipid bilayer, in which the enzyme is located, also controls the interaction between protomers and that changes in their biophysical properties can modulate the activity of the enzyme. The objective of this study was to investigate the effect of different detergent/protein ratios on the stability solubilized of Na, K-ATPase and different lipid microenvironments in their activity by analyzing changes in the thermotropic behavior of the bilayer, analysing the incorporation changes and the recovery of enzyme activity when the protein was reconstituted in a membrane mimetic systems. Dynamic light scattering (DLS) was used to monitor the process of thermal aggregation of the enzyme, providing information on their structure and evaluating its stability when solubized. The thermal denaturation of Na, K-ATPase was also evaluated by differential scanning calorimetry (DSC) and it was verified that it is an irreversible process, which occurred between 50 and 70 ° C, being the sum of three transitions. Using DSC, we analyzed the thermotropic behavior of proteolipossomos and liposomes consisting of DPPC, DPPE and cholesterol. For vesicular systems in the absence of the protein, it was observed that for the binary system of DPPC and DPPE, increasing the proportion of the latter induces a lipid phase separation and the presence of cholesterol in both binary systems (DPPC: Col and DPPE: Chol), and in the ternary system (DPPC: DPPE: Chol) it induces a lipid phase separation. It was also evaluated how the lipid microenvironment interferes on the incorporation and activity of Na, K-ATPase. It was found that different amounts of cholesterol alter the enzyme activity, confirming cholesterol has an important role in the modulation of the activity by altering the membrane properties and influencing the protein conformation.

The increasing demands for biopharmaceuticals to treat different diseases have raised concerns about controlling the quality and efficacy of such pharmaceuticals. The design and formulation of a stable protein or peptide based biopharmaceutical runs into the limitation that at high concentrations (> 100 mg/ml) or during long storage process the drug undergoes aggregation. During synthesis, purification, storage or packaging of these drugs different kinds of stresses like chemical, oxidative, thermal, shear, etc. are encountered. These stresses promote the non-native aggregation of protein and peptide based drugs. Injection or administration of such drugs if contaminated with aggregates causes patient discomfort or development of an antibody which can adversely affect patient’s conditions. This brings out the necessity of finding a way so that such aggregation is avoided. Nanoparticles have been used as vehicles for drug delivery and diagnostic agents in biology for a while. The surface of the nanoparticles is known to adsorb small as well as large molecules with different kinetics and energetics of interaction. I have used nanoparticles to adsorb proteins to protect them against aggregation when they are subjected to denaturing conditions. The effectiveness of the nanoparticles in stopping protein aggregation, recovery of the proteins and reversibility of the adsorption process, the catalytic activity of the proteins before and after adsorption on the surface have all been studied in details. The work described here has been divided in 8 chapters and the contents of each chapter are described below. In Chapter 1 I have provided a brief introduction to the protein aggregation problem. The motivation and scope of the current work has been presented in this chapter. Materials and methods have been described in Chapter 2. Synthesis of gold and silica nanoparticles, their characterization and stability under experimental conditions have been illustrated in this chapter. The spectroscopic assays and techniques which I have used to study the effect of gold and silica nanoparticles on protein aggregation have been discussed at lengths in this chapter. In Chapter 3 I have demonstrated the effect of gold nanoparticles on thermal aggregation of alcohol dehydrogenase (ADH). The size of the nanoparticle was varied in the range of 15-60 nm and the effect was measured by various spectroscopic assays and techniques. I have observed that gold nanoparticles prevent thermal aggregation of ADH and the efficiency is high. Gold nanoparticles in nanomolar or even picomolar concentrations are capable of preventing the aggregation of ADH at micromolar concentrations. In Chapter 4 the role of gold nanoparticles as suppressor of protein aggregation was extended to another protein, insulin. Chemically induced aggregation of insulin using dithiothreitol (DTT) in the presence of gold nanoparticles was studied in the same manner as was done for ADH. Similar prevention property of gold nanoparticles was established by making the observation independent of the method of denaturation or the type of protein used in the prevention experiments. In Chapter 5 huge second harmonic light scattering (SHS) signal from pure gold nanoparticles has been used to measure the free energy of interaction of ADH and insulin with nanoparticles in solution, for the first time. The change in the second harmonic scattered signal was monitored which decreased steadily as a function of added protein concentration to the aqueous solution of gold nanoparticles. The fitting of the second harmonic signal decay was done with a modified Langmuir adsorption isotherm to extract the free energy change in the interaction and the number of protein molecules adsorbed on the surface. In Chapter 6 I have demonstrated a way to recover the adsorbed ADH and insulin from the gold nanoparticle surface and tested the activity of ADH by an assay. The structure of the proteins in the adsorbed state has been probed by CD spectroscopy and described in this chapter. It is found that ADH retains its activity in the adsorbed state. Both the proteins retain the native secondary structures in their adsorbed state. However, the structures change drastically under denaturing conditions. In Chapter 7 the effect silica nanoparticles which are known to have hydrophilic surface has been examined on the aggregation of ADH and insulin in pretty much the same way as was done with gold nanoparticles. The efficiency of silica nanoparticle was found to be lower compared to gold nanoparticles. In addition, the size dependency of prevention efficiency of silica and gold nanoparticles was found to be completely opposite to each other. In Chapter 8 I have presented the overall summary and possible future directions of this work