Study On The Self-assemble Of Amyloid Peptide And Applications Of Amyloid Peptide Assemblies

Amyloid peptide assemblies are common in nature and have been well-known due to its relationship with neurodegenerative diseases such as Alzheimer’s disease,Parkinson’s disease,Huntington disease and so on.Therefore,extensive efforts have been devoted to elucidate the pathway of amyloid deposit formation and the mechanism for its neurotoxicity.However,much attention have also been transferred to use the amyloid assemblies in materials science and nanotechnology,because of their well-defined nanostructure,high aspect ratio,good stability,excellent biocompatibility,easy to production and low cost.Based on different characteristics of self-assembled KL-7（Ac-KLVFFAL-NH₂）amyloid peptide nanotube,three functional materials have been developed in this paper.We first investigated the effect of KL-7 peptide nanotube on the hydrolysis rate of p-NPA（4-nitrophenyl acetate）.The enhancement of p-NPA hydrolysis by KL-7 nanotubes can be attributed to the formation of hydrophobic microenvironments which are able to lower the p K_a of the lysine.The raction mechanism have been proved and we have successfully achieved the control of hydrolysis rate.Besides,a fluorescently-labeled peptide FAM-Heme-KD-8（FAM-Heme-KLVFFAED-NH₂）was designed based on the electropositivity of the KL-7 nanotube,the selective recognition of the Aβaggregation state have realized by competitive adsorption of FAM-Heme-KD-8 and Aβon the KL-7 nanotube,and then this system was applied to screen Aβanti-aggregation reagents.What’s more,solid state KL-7 nanotube powder was developed to capture electrophilic carbon dioxide gas molecule through the nucleophilicity of the amino groups on the surface of the KL-7 nanotube.Compared to other carbon dioxide absorbents,KL-7 nanotube powder showed good regeneration property and compatibility in the presence of water.This paper is mainly divided into the following four chapters:Chapter 1.IntroductionThis chapter first overview the amyloid peptide assemblies,including the development of the self-assembled peptide and it’s applications in material science,and KLVFF-based peptide assemblies.Then we introduce the artificial hydrolases,Aβbiosensors and carbon dioxide adsorbents,respectively.Finally,the research contents in this paper are summarized.Chapter 2.The effect of amyloid nanostructures on p-NPA hydrolysis rateIn this chapter,we investigated the effect of peptide nanotube self-assembled by heptapeptide（Ac-KLVFFAL-NH₂,KL-7）on p-NPA（4-nitropheyl acetate）hydrolysis rate.Different from the catalytically active sites such as histidine,serine or cysteine residues present in typical artificial hydrolase,we demonstrate that KL-7 nanotubes employ lysine residues exposed outside the nanotube bilayer as nucleophiles in hydrolysis.Subsequently,we proposed a reaction mechanism of KL-7 nanotube with p-NPA and confirmed it by detecting the existence of the acylated peptide product.Importantly,thanks to the rich chemistry of amino group of lysine,we have successfully realized the regulation of the hydrolysis rate of p-NPA by reversibly protecting and deprotecting the amino group after multiple cycles.Chapter 3.Aβaggregation state recognition based on competitive adsorption of FAM-Heme-KD-8 and Aβon peptide nanotube surfaceIn this chapter,afluorescently-labeledpeptide FAM-Heme-KD-8（FAM-Heme-KLVFFAED-NH₂）was designed.When adding FAM-Heme-KD-8 into the self-assembled KL-7（Ac-KLVFFAL-NH₂）nanotube,the FAM-Heme-KD-8 was adsorbed on the nanotube surface through electrostatic interaction,in the meantime,the fluorescence of FAM was quenched due to the aggregation-caused quenching effect.However,after adding Aβ,the Aβinteracted with FAM-Heme-KD-8 through H-bonded interaction and hydrophobic interaction,and the fluorescence was recovered because FAM-Heme-KD-8 was away from the nanotube surface.Due to the interaction between Aβand FAM-Heme-KD-8 varies from the aggregation state of Aβ,through the difference in fluorescence intensity,the aggregation state of Aβwas able to be distinguished.In addition,because of the specificity of Heme to Aβ,compared to other proteins,this system showed good selectivity to Aβ.What’s more,this system was able to screen Aβanti-aggregation reagents,and the ThT assay and TEM characterization were performed to validate the results.Chapter 4.Study on carbon dioxide chemisorption by peptide nanotubeIn this chapter,we demonstrate that peptide nanotubes self-assembled from a heptapeptide Ac-KLVFFAL-NH₂（KL-7）with amino groups exposed on the surface for selective carbon dioxide chemisorption.It has been proved that the reaction product carbamate was formed through solid-state NMR,thus we proposed a mechanism of carbon dioxide reacted with KL-7 nanotube.What’s more,The KL-7nanotube powder showed good regeneration properties with negligible carbon dioxide uptake change after multiple absorption-desorption cycles and the moderate regeneration temperature（100℃）of KL-7 nanotube made it more energy-efficient.It is also shown that water vapor almost have no influence on the carbon dioxide adsorption capacity of KL-7 nanotube,since water vapor is one of the key components in practical gas mixtures and the fact that preferential adsorption of water vapor over carbon dioxide will decrease the carbon dioxide adsorption capacities of physisorbents.