Over 60 proteins have been detected in the tear film and among these lysozyme has attracted the greatest attention. Several techniques for elucidating the identity, quantity and conformation of lysozyme deposited on soft contact lenses have been developed. Lysozyme also deposits on the newly introduced silicone hydrogel (SH) lens materials, but in extremely low levels compared to conventional hydrogel lenses. Hence, a major analytical complication with the study of the SH contact lens materials relates to the minute quantity of deposited lysozyme. The first project of this thesis involved the development of a method whereby lysozyme mass extracted from SH lens materials would be preserved over time and would be compatible with an optimized Western blotting procedure. This methodological development was incorporated into a clinical study (CLENS-100?? and Silicone Hydrogels ? CLASH study) wherein the difference in the degree of total protein, the difference in lysozyme deposition and activity recovered from lotrafilcon A SH lens material when subjects used surfactant containing rewetting drops (CLENS-100??) versus control saline was investigated. The remaining experiments were in vitro experiments wherein the lenses were doped in artificial lysozyme solution containing ¹²⁵I-labeled lysozyme. These experiments were performed to gain insight into the kinetics of lysozyme deposition on SH lens materials and also the efficacy of a reagent in extracting lysozyme from SH lens materials. A protocol was developed whereby the percentage loss of lysozyme mass found on lotrafilcon A SH lenses was reduced from approximately 33% to <1% (p<0. 001), following extraction and resuspension. The results from the CLASH study demonstrated that when subjects used a surfactant containing rewetting drop instead of a control saline drop total protein deposition (1. 2??0. 7 ??g/lens versus 1. 9??0. 8 ??g/lens, p<0. 001), lysozyme deposition (0. 7??0. 5 ??g/lens versus 1. 1??0. 7 ??g/lens, p<0. 001) and percentage lysozyme denaturation (76??10% versus 85??7%, p=0. 002) were all reduced. The results from the kinetics study demonstrated that lysozyme accumulated rapidly on etafilcon A lenses (1 hr, 98??8 ??g/lens), reached a maximum on the 7th day (1386??21 ??g/lens) and then reached a plateau (p=NS). Lysozyme accumulation on FDA Group II and SH lenses continued to increase across all time periods, with no plateau being observed (p<0. 001). The results from the extraction efficiency study showed that 0. 2% trifluoroacetic acid/ acetonitrile was 98. 3??1. 1% and 91. 4??1. 4% efficient in extracting lysozyme deposited on etafilcon A and galyfilcon lenses, while the lysozyme extraction efficiency was 66. 3??5. 3 % and 56. 7??3. 8% for lotrafilcon A and balafilcon lens materials (p<0. 001). The results from these studies re-emphasize that novel SH lens materials are highly resistant to protein deposition and demonstrate high levels of biocompatibility.

No description available.

Les effets d'une pression hydrostatique non dénaturante (3kbar) sur les mouvements internes du lysozyme sont étudiés selon deux approches conjuguées : la dynamique moléculaire et la diffusion quasiélastique de neutrons qui couvrent les mêmes échelles de temps et de distance. Les simulations montrent une compaction du lysozyme avec la pression et une diminution des fluctuations atomiques surtout aux basses fréquences. La partie quasiélastique de la fonction de diffusion subit un léger abaissement difficilement mis en évidence dans les résultats expérimentaux. Les simulations reproduisent correctement le profil des spectres expérimentaux et le modèle Brownien fractionnaire est pertinent pour rendre compte des multiples temps de relaxation caractérisant la dynamique interne d'une protéine.

Circular dichroism (CD) spectra were obtained for bacteriophage T4 lysozyme and three of its mutants in the presence and absence of colloidal silica nanoparticles. Mutant lysozymes were produced by substitution of the isoleucine at position 3 with tryptophan, cysteine and leucine. Each substitution resulted in an altered structural stability, quantified by a difference in free energy of unfolding from the wild type. CD spectra recorded in the absence of colloidal silica agreed with x-ray diffraction data in that the mutants and wild type showed similar secondary structures. CD spectra of protein-nanoparticle complexes recorded after contact for 90 minutes showed significant differences from those recorded in the absence of nanoparticles, and these differences varied among the proteins. The percentage of a-helix lost in these proteins upon adsorption to silica nanoparticles was also recorded as a function of time by CD. For a 1:2 protein to particle mixture, different kinetic behaviors were observed among the proteins. The more unstable the protein, the greater the rate and extent of secondary structure loss upon adsorption. For a 1:1 protein to particle mixture, only results recorded with the tryptophan mutant were significantly different from the other variants. The kinetic data recorded for the 1:2 protein to particle ratio was evaluated using two different protein adsorption models. Both models allow proteins at an interface to exist in two different states: state 1 molecules retain their native conformation, while state 2 molecules lose a certain amount of their native secondary structure and occupy more surface area than state 1 molecules. The main difference between these two models is that one allows state 2 molecules to be adsorbed directly from solution, while the other requires that state 2 molecules be generated by surface-induced conversion of state 1 molecules. The former model showed a better fit to the data than the latter from a least squares comparison. Both models indicated that proteins of lower thermal stability have a greater tendency to adopt state 2 on silica. / Graduation date: 1997

Quantum dots (QDs) of II-VI semiconductors (CdS, CdSe, and CdTe) in the size range of 1~12 nm have attracted great interest in both fundamental research and technical applications in recent years. Due to their tunable size-dependent emission with high photoluminescence quantum yields, their broad excitation spectra and narrow emission bandwidths, the semiconductor QDs have been intensively investigated in versatile applications, including thin-film light emitting devices (LEDs), low-threshold lasers, optical amplifier media for telecommunication networks and biological labels. Thus, constructing and fabricating highly ordered QDs are of great importance in the field of nanotechnology. The surface chemistry behavior of the TOPO-CdSe QDs and TOPO-(CdSe)ZnS QDs at the air-water interface was carefully examined by various physical measurements. The surface pressure-area isotherms of the Langmuir monolayers of both types of QDs gave the average diameter which matched the value determined by TEM measurements. Topographic study of the Langmuir monolayers of both QDs revealed the 2D aggregation during the early stage of the compression process. The stability of the Langmuir monolayer of the TOPO-(CdSe)ZnS QDs was measured by the compression/decompression cycle and the kinetic measurements, both of which indicated that TOPO capped (CdSe)ZnS QDs can form stable Langmuir monolayers at the air-water interface. Langmuir-Blodgett (LB) film of the TOPO-(CdSe)ZnS QDs were prepared on quartz slides at different surface pressures and characterized by photoluminescence (PL) spectroscopy. The linear increase of the PL intensity with the increase of the number of layers deposited onto the quartz slide implied a homogeneous deposition of the Langmuir monolayer. The conjugates of 10, 12-pentacosadiynoic acid (PDA) and short chain peptide was used to modify the surface of (CdSe)ZnS core-shell QDs. The PDA-peptide capped QDs formed stable Langmuir monolayer. After the photopolymerization of PDA-peptide-QDs/PDA-peptide system at the air-water interface, a more uniform and robust Langmuir monolayer was constructed. The 3-mercaptopropyltrimethoxysilane (MPS) was linked to (CdSe)ZnS QDs by ligand exchange method. The sol-gel process of the MPS capped QDs Langmuir monolayer was studied under various subphases of pH and reaction time. The fast sol-gel process under a subphase of pH 12.0 led the formation of a more homogeneous Langmuir monolayer. A smooth MPS-QDs LB film deposited under pH 12.0 was also observed by AFM measurements. The imaging of the aggregates of lysozyme using lysozyme/(CdSe)ZnS QDs conjugate as a PL label was investigated. The amyloid fibrils formed by lysozyme/lysozyme-QDs conjugate were observed by epifluorescence microscopy, atomic force microscopy (AFM) and transmission electron microscopy (TEM) measurements. The emission intensity of the QDs labeled lysozyme was increased about 3 fold after formation of amyloid. This approach, for the first time, provided a convenience method to image the amyloid fibrils by epifluorescence microscopy.

Accumulation or aggregation of amyloidogenic proteins in the brain plays a central role in neurodegenerative diseases. The most common and highly growing form of dementia in the elderly population is Alzheimer's disease (AD) followed by Parkinson's disease (PD). The major proteins associated are amyloid beta (Abeta) and alpha-synuclein (alpha-syn) in AD and PD, respectively. These proteins are released or found near the neuronal membranes in the brain. Consequently to understand the behavior of the proteins using a model membrane system becomes an important facet of understanding these diseases. Langmuir monolayer approach was used to study the surface chemistry and spectroscopy of Abeta (1-40), Abeta(1-42) and alpha-synuclein. Moreover, surface chemistry of a model protein namely, lysozyme was investigated. In recent times, quantum dots (QDs) are considered as potential probes for bio-imaging. These particles can be beneficial when it comes to the investigation of neurodegenerative diseases. The effect of nanoparticles, i.e., CdSe/ZnS QDs on Abeta (1-42) morphology was investigated. Nevertheless, it was observed that the capping ligand plays a significant role in the surface chemistry of QDs when mixed with or conjugated to Abeta (1-42). Surface pressure- and surface potential-area isotherms were used to characterize the lysozyme Langmuir monolayer. The compression-decompression cycles and stability measurements showed a homogeneous and stable monolayer at the air-water interface. Salt concentration in the subphase and pH of the subphase were parameters controlling homogeneity and stability of the Langmuir monolayer. In situ UV-vis and fluorescence spectroscopies were used to verify the homogeneity of the lysozyme monolayer, and to identify the chromophore residues in the lysozyme. Optimal experimental conditions were determined to prepare a homogeneous and stable lysozyme Langmuir monolayer. The surface chemistry and spectroscopy of the reduced lysozyme Langmuir monolayer were investigated at different pH values and were compared to a native lysozyme. It was established that the limiting molecular area of the reduced lysozyme was not subphase pH dependent as was found for the native one. To explain this result in terms of the conformation and orientation of the lysozyme Langmuir monolayer at various subphase pH values, we have used Infrared Reflection Absorption Spectroscopy (IRRAS). The interpretation of the results suggests a change in the conformation and orientation of the native lysozyme Langmuir monolayer with the subphase pH 3, 6 and 11. The surface chemistry of Abeta (1-40) and its interaction with the lipid raft Langmuir monolayer were examined where the stability of the lipid raft Langmuir monolayer came out as an essential parameter. Lipid raft Langmuir monolayer in the presence or absence of ganglioside GM1 having POPC as one of the phospholipids was found to be very unstable and collapsed within 26 min. Whereas, the phospholipid DPPG improved the stability of the monolayer significantly when cholesterol was used in excess. We have examined the surface and spectroscopic properties of Abeta (1-42) mixed with or conjugated to dihydrolipoic acid (DHLA)- and polyethylene glycol (PEG)- capped CdSe/ZnS QDs. Surface pressure-area isotherms, in situ UV-vis absorption, and fluorescence spectroscopy were used to characterize the Abeta (1-42) mixed with or conjugated to QDs at the air-water interface. The capping of QDs played a role in surface chemistry as was determined by surface pressure-area isotherms and spectroscopic properties of the Langmuir monolayer. Furthermore Abeta(1-42) was bioconjugated to DHLA-capped CdSe/ZnS QDs. Upon conjugation of Abeta (1-42) to DHLA-capped QDs, the sample was incubated at 37oC, the process of fibrillation was inhibited as compared with a sample where Abeta (1-42) was simply mixed with the QDs. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) were employed for the analysis of the samples. The morphology of fibrils and reduction in number of fibrils was substantial in the case of Abeta(1-42) conjugated to QDs. Reduction in fibrillation was also confirmed using a Thioflavin T assay. Moreover, quenching of tyrosine signal was observed in presence of the QDs, which indicates an interaction of QDs to the tyrosine residue in Abeta (1-42). The Surface chemistry and spectroscopy of alpha-syn, which is a natively unstructured protein important in the neuropathology of PD was investigated. IRRAS was utilized to investigate its conformation, alpha-syn was found to form a Langmuir monolayer in alpha-helical conformation with its helical axis parallel to the air-water interface.

Protein aggregation, leading to the formation and depositions of amyloids, is a cause for a number of diseases such as Alzheimer’s and Creutzfeld-Jacob’s disease, systemic amyloidoses, type II diabetes and others . More than 20 proteins are associated with protein misfolding diseases and even a larger number of proteins can self-assemble into amyloid in vitro. Relating structural and functional properties of amyloid is of particular interest, as this will lead to the identification of the main factors and mechanisms involved in the process of protein misfolding and aggregation; consequently, this will provide a basis for developing new strategies to treat protein misfolding diseases. The aim of the thesis is to investigate structural aspects of amyloid formation and relate that to the functional properties of amyloid. The first paper describes the amyloid formation of equine lysozyme (EL). We have demonstrated that EL enters an amyloid forming pathways under conditions where the molten globule state is populated. We have found that the morphology of the amyloids depend on the calcium-binding to lysozyme, specifically the holo-protein assembles into short, linear protofilaments, while the apo-EL forms ring-shaped structures. The morphology of EL amyloid significantly differs from the amyloid fibrils of human and hen lysozymes. We have suggested that the stable alpha-helical core of EL, which remains structured in the molten globule intermediate, may obstruct the formation of fibrilar interface and therefore leads to assembly of short, curly fibrils and rings.In the second paper, we describe the cytotoxicity of EL amyloids. We have analysed the amyloid intermediates on the pathway towards amyloid fibrils. The sizes of amyloid oligomers were determined by atomic force microscopy (AFM) and the formation of cross-beta sheet was shown by thioflavin T (ThT) binding. The toxicity studies show that the oligomers formed during amyloid growth phase are toxic to a range of cell lines and cultures and the toxicity is size-dependant.The last manuscript describes a novel method for manufacturing of silver nanowires by the biotemplating using amyloid fibrils. The amyloid assembled from an abundant and cheap hen egg white lysozyme was used as a scaffold for casting ultrathin silver nanowires. We have manufactured nanowires with a diameter of 1.0-2.5 nm and up to 2 micrometers in length. Up to date, it is the thinnest silver nanowires produced by using biotemplating and at least one order of magnitude thinner than nanowires manufactured by chemical synthesis.

Over 60 proteins have been detected in the tear film and among these lysozyme has attracted the greatest attention. Several techniques for elucidating the identity, quantity and conformation of lysozyme deposited on soft contact lenses have been developed. Lysozyme also deposits on the newly introduced silicone hydrogel (SH) lens materials, but in extremely low levels compared to conventional hydrogel lenses. Hence, a major analytical complication with the study of the SH contact lens materials relates to the minute quantity of deposited lysozyme. The first project of this thesis involved the development of a method whereby lysozyme mass extracted from SH lens materials would be preserved over time and would be compatible with an optimized Western blotting procedure. This methodological development was incorporated into a clinical study (CLENS-100® and Silicone Hydrogels ? CLASH study) wherein the difference in the degree of total protein, the difference in lysozyme deposition and activity recovered from lotrafilcon A SH lens material when subjects used surfactant containing rewetting drops (CLENS-100®) versus control saline was investigated. The remaining experiments were in vitro experiments wherein the lenses were doped in artificial lysozyme solution containing ¹²⁵I-labeled lysozyme. These experiments were performed to gain insight into the kinetics of lysozyme deposition on SH lens materials and also the efficacy of a reagent in extracting lysozyme from SH lens materials. A protocol was developed whereby the percentage loss of lysozyme mass found on lotrafilcon A SH lenses was reduced from approximately 33% to <1% (p<0. 001), following extraction and resuspension. The results from the CLASH study demonstrated that when subjects used a surfactant containing rewetting drop instead of a control saline drop total protein deposition (1. 2±0. 7 µg/lens versus 1. 9±0. 8 µg/lens, p<0. 001), lysozyme deposition (0. 7±0. 5 µg/lens versus 1. 1±0. 7 µg/lens, p<0. 001) and percentage lysozyme denaturation (76±10% versus 85±7%, p=0. 002) were all reduced. The results from the kinetics study demonstrated that lysozyme accumulated rapidly on etafilcon A lenses (1 hr, 98±8 µg/lens), reached a maximum on the 7th day (1386±21 µg/lens) and then reached a plateau (p=NS). Lysozyme accumulation on FDA Group II and SH lenses continued to increase across all time periods, with no plateau being observed (p<0. 001). The results from the extraction efficiency study showed that 0. 2% trifluoroacetic acid/ acetonitrile was 98. 3±1. 1% and 91. 4±1. 4% efficient in extracting lysozyme deposited on etafilcon A and galyfilcon lenses, while the lysozyme extraction efficiency was 66. 3±5. 3 % and 56. 7±3. 8% for lotrafilcon A and balafilcon lens materials (p<0. 001). The results from these studies re-emphasize that novel SH lens materials are highly resistant to protein deposition and demonstrate high levels of biocompatibility.

This study describes the use of human serum albumin (HSA)-modified gold nanoparticles (HSA-AuNPs) for the selective extraction and enrichment of high-pI protein, lysozyme (Lyz) prior to analysis by capillary electrophoresis (CE) with UV detection. HSA-AuNPs are capable of extracting Lyz from a complicated matrix because a HSA capping layer not only stabilizes gold nanoparticles in a high-salt environment but also exhibits strong electrostatic attraction with Lyz under neutral pH condition. Efficient separation of Lyz and other high-pI proteins has been successfully achieved by the filling of cationic polyelectrolyte, poly(diallydimethylammonium chloride) (PDDAC), to the background electrolyte. After capturing Lyz with HSA-AuNPs, PDDAC-filled CE can be directly used for the analysis of the extracted Lyz without the addition of the releasing agent into the extractor. The extraction efficiency relied on the pH of the solution and the concentration of HSA-AuNPs. Under optimal extraction conditions, the limits of detection at a signal-to-noise ratio of 3 for Lyz were down to 8 nM. The combination of HSA-AuNP extraction and PDDAC-filled CE has been applied the analyses of lysozyme in chicken egg white, white wine and human tear. Also, we reveal that this NP-based extraction can be coupled to matrix-assisted desorption/ionization time-of-flight mass spectrometry.

Reproduction de : Thèse de doctorat : Sciences des matériaux : Lille 1 : 2005. / N° d'ordre (Lille 1) : 3705. Résumé en français et en anglais. Titre provenant de la page de titre du document numérisé. Bibliogr. p. 167-175.