Microcavity supported lipid membranes: versatile platforms for building asymmetric lipid bilayers and for protein recognition

Microcavity supported lipid bilayers (MSLB) are contact-free membranes suspended across aqueousfilled pores that maintain the lipid bilayer in a highly fluidic state and free from frictional interactions with substrate. Such platforms offer the prospect of liposome-like fluidity with the compositional versatility and addressability of supported lipid bilayers and thus offer significant opportunity for modelling membrane asymmetry, protein-membrane interactions and aggregation at the membrane interface. Herein, we evaluate their performance by studying the effect of transmembrane lipid asymmetry on lipid diffusivity, membrane viscosity and cholera toxin- ganglioside recognition across six symmetric and asymmetric membranes including binary compositions containing both fluid and gel phase, and ternary phase separated membrane compositions. Fluorescence lifetime correlation spectroscopy (FLCS) was used to determine the lateral mobility of lipid and protein, and electrochemical impedance spectroscopy (EIS) enabled detection of protein-membrane assembly over the nanomolar range. Transmembrane leaflet asymmetry was observed to have profound impact on membrane electrochemical resistance where the resistance of a ternary symmetric phase separated bilayer was found to be at least 2.6 times higher than the asymmetric bilayer with analogous composition at the distal leaflet but where the lower leaflet comprised only 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). Similarly, the diffusion coefficient for MSLBs was observed to be 2.5 fold faster for asymmetric MSLBs where the lower leaflet is DOPC alone. Our results demonstrate that interplay of lipid packing across both membrane leaflets and concentration of GM1 both affect the extent of cholera toxin aggregation and consequent diffusion of the cholera-GM1 aggregates. Given that true biomembranes are both fluidic and asymmetric, MSLBs offer the opportunity for building greater biomimicry into biophysical models and the approach described demonstrates the value of MSLBs in studying aggregation and membrane associated multivalent interactions prevalent in many carbohydrates mediated processes

Versatile cell membrane models: biomimetic suspended lipid bilayers designed for protein/DNA membrane dynamics and detection

The cell membrane, comprised mainly of phospholipid, sphingolipids, sterols and proteins, is a complex, but molecularly ordered, semi-permeable barrier between the intracellular and extracellular environments. It plays a vital role in cell adhesion, signaling and transport. To understand its functions, in many cases to reduce experimental complexity in the study of lipids and proteins several model membrane systems have been developed in the past years. This thesis explores the application of one such model Microcavity-Supported Lipid Bilayers, or MSLBs, as a versatile platform for the preparation and the study of asymmetric lipid bilayers containing gangliosides. The overall objective of the thesis is therefore to explore the application of microcavity supported lipid bilayers and their use as versatile platforms to the preparation of highly fluidic lipid membranes to study important biophysical aspects of membranes such lipid asymmetry, protein-binding, protein incorporation to suspended lipid membranes and protein aggregation. In addition, the lipid bilayers spanned over microcavity arrays were used as a model for oligonucleotide endosomal escape from cationic lipoplexes. Chapter 1 describes the background to this work and overviews the current state of the art in model membranes. In chapter 2, describes experimental studies at the MSLBs to evaluate fluidity of symmetric and asymmetric lipid bilayers in parallel with an interrogation of binding of Cholera Toxin subunit b (CTb) to its receptor GM1. It was found that transmembrane asymmetry affects the lipid bilayer fluidity in MSLBs. The lateral clustering of CTb was observed at the nanomolar range in fluidic and gel-phase membranes. As will be discussed, the high lateral fluidity of the MSLBs along with their multimodal addressability makes them really well suited to building both asymmetric bilayers, in analogy to the real cell membrane. And in particular to the study of aggregation processes involving lateral movement of lipid and/or membrane protein. Aggregation xiv is a feature of a number of key biological processes including infection and, in this work, MSLBs are applied to two infection models: cholera toxin and in chapter 3 hemagglutinin. In chapter 3, the binding of hemagglutinin (HA1) from influenza virus was demonstrated to be dependent on the type of ganglioside and on the lipid bilayer composition. The affinity of three glycolipids GDa1, GM1 and GM3 for the subunit HA1 suggested that GDa1 showed highest affinity at DOPC bilayers, even though the diffusivity of GDa1-HA1 complex was approximately half of that obtained for GM1 and GM3-HA1 complexes suggesting differences in HA1 assembly dimensions or penetration into the lipid bilayer. Although the affinity of HA1 for GM1 appears unaffected by lipid bilayer composition, the lower mobility of HA1 in bilayers containing sphingomyelin and cholesterol suggests association with Lo domains. These results suggest that the affinity of HA1 is dictated by GSL and lipid membrane composition and might suggest that these characteristics could influence the target cell for influenza infection. Another key advantage of MLSBs is that they offer a substantial aqueous volume above and below the lipid membrane and so unlike SLBs, can support both structurally and in terms of diffusion transmembrane proteins. Chapter 4, membrane protein reconstitution was explored using bacteriorhodopsin as a photo-active proton pump to create a simple photoresponsivity machine from MSLB focused on the insertion of a photo-activated proton pump, bacteriorhodopsin (bR), into artificial cavity-spanning lipid bilayers. It was found that the photo-activation of lipid bilayers containing bR generate an electric response, which is dependent on frequency of the transient photo-signal and environmental pH. Chapter 5 expands the use of MSLBs and explores the use of MSLBs to study the delivery and release of oligonucleotide-cargo from lipoplexes to microcavities to stablish a proof-of-concept assay for oligonucleotide endosomal escape platform using SERS and FLCS. In order to mimic as close as possible a typic mammalian cell membrane, a quaternary membrane composition was used. It was found that the fastest oligonucleotide cargo release was obtained for the cationic lipoplexes comprised of DOTAP/DOPE. This indicates a new direction of the use of MSLBs to the study of nanocarrier gene delivery. Finally, chapter 6 focused on building a model of Galectin- 3 (Gal3) binding to integrin α5β1 and to gangliosides. The insertion of α5β1 into MSLBs was used to determine its lateral diffusion coefficient and aggregation. It was found that Gal3 reorganizes the spatial distribution of GSLs in an oligomerization-dependent manner, and the bounding of Gal3 to integrin leading to an increase in α5β1 mobility

Síntese e caracterização de materiais calcogenetos híbridos, GeS2

O crescimento da indústria demanda materiais cada vez mais eficientes. Os materiais à base de calcogenetos híbridos estruturados são de grande interesse para o desenvolvimento de novas tecnologias e com aplicações nas mais diversas áreas. Este trabalho consiste em estudar uma nova rota de síntese em fase liquida para materiais calcogenetos híbridos do tipo GeS2 estruturados. A utilização de líquidos iônicos como agentes estruturantes tem sido estudada em diversas áreas e permite a obtenção de materiais híbridos porosos e de grande superfície especifica. Porém, a incorporação da parte catiônica dos líquidos iônicos podem alterar as características abrindo espaço para novas aplicações na de separação de gases, em catalise e na estocagem de energia. Foram testados como agentes estruturantes o Bmim[NTF2] e o Li[NTF2] em diferentes concentrações. Os materiais obtidos são caracterizados buscando investigar a estrutura segundo as diferentes formas de reações utilizadas, enquanto que a solução residual foi caracterizada por RMN H1 e C13 visando uma melhor compreensão do mecanismo químico envolvido neste trabalho.The growth of industry demands even more efficient materials. Structured hybrid chalcogenide-based materials are of great interest for the development of new technologies and applications in several areas. This work studies a new way to synthesize the GeS2 structured chalcogenide materials in its liquid phaseThe use of ionic liquids as structuring agents has been studied in different areas and allows to obtain porous hybrid materials and high specific surface. However, the incorporation of cationic part of the ionic liquids can change the proprieties, making way for new applications like in gas separation, catalysis and in the storage of energy. Structuring agents were tested as the BMIM[NTF2] and Li[NTF2] at different concentrations. The materials obtained are characterized to investigate the structure according to the different types of reactions used, while the residual solution was characterized by H1NMR and C13 to understand the chemical mechanism described in the synthesis

Síntese e caracterização de materiais calcogenetos híbridos, GeS2

O crescimento da indústria demanda materiais cada vez mais eficientes. Os materiais à base de calcogenetos híbridos estruturados são de grande interesse para o desenvolvimento de novas tecnologias e com aplicações nas mais diversas áreas. Este trabalho consiste em estudar uma nova rota de síntese em fase liquida para materiais calcogenetos híbridos do tipo GeS2 estruturados. A utilização de líquidos iônicos como agentes estruturantes tem sido estudada em diversas áreas e permite a obtenção de materiais híbridos porosos e de grande superfície especifica. Porém, a incorporação da parte catiônica dos líquidos iônicos podem alterar as características abrindo espaço para novas aplicações na de separação de gases, em catalise e na estocagem de energia. Foram testados como agentes estruturantes o Bmim[NTF2] e o Li[NTF2] em diferentes concentrações. Os materiais obtidos são caracterizados buscando investigar a estrutura segundo as diferentes formas de reações utilizadas, enquanto que a solução residual foi caracterizada por RMN H1 e C13 visando uma melhor compreensão do mecanismo químico envolvido neste trabalho.The growth of industry demands even more efficient materials. Structured hybrid chalcogenide-based materials are of great interest for the development of new technologies and applications in several areas. This work studies a new way to synthesize the GeS2 structured chalcogenide materials in its liquid phaseThe use of ionic liquids as structuring agents has been studied in different areas and allows to obtain porous hybrid materials and high specific surface. However, the incorporation of cationic part of the ionic liquids can change the proprieties, making way for new applications like in gas separation, catalysis and in the storage of energy. Structuring agents were tested as the BMIM[NTF2] and Li[NTF2] at different concentrations. The materials obtained are characterized to investigate the structure according to the different types of reactions used, while the residual solution was characterized by H1NMR and C13 to understand the chemical mechanism described in the synthesis