Study On The Template-assisted Self-assembly Of Peptides

Currently, there are about 24.3 million Alzheimer’s (Alzheimer’s) patients (half of them in the Asia-Pacific region), and the data keeps growing with a rate of 4.6 million a year. Previous investigations shown that some relevant peptides form insoluble fibers which gradually deposit in cells and result in cell death due to the loss of the relevant cellular functions, a reason for Alzheimer’disease. Other similar diseases have also been discovered, such as Parkinson’s disease, Huntington’s disease, Amyotrophic lateral sclerosis, and so on, which are now collectively known as neurodegenerative diseases. Hence, it is of paramount to study the fibrosis of amyloid proteins, and furthermore to analyze the core sequences/peptides which cause the fibrosis. This study may shed light a better understanding of the pathogenesis of these diseases, and a good exploration of the ways for treatments and cure. The fibrosis of peptides is actually a self-assembly process, which is very prevalent in vivo. Peptides can be designed and synthesized nowadays, which can self-assemble into a variety of nanostructures such as vesicles, microspheres, nanorods, nanotubes, nano-films. These nanostructures have played an more and more important roles in the field of materials science and nano-biomedicine.In this study, by using the scanning probe microscopy (SPM) combining the in situ observation method and micro-contact printing technology, I have studied the effect of temperature on the self-assembly process of a disease-related peptide GAV-9 (NH2-VGGAVVAGV-CONH2) in nano-water film. The self-assembly processes under different solution conditions have also been investigated by using another synthesized peptide. In the first part of this dissertation, the influence of temperature on the GAV-9 self-assembly is studied, and the results show:1) The speed of GAV-9 self-assembly into fiber structure is positively correlated with temperature; 2) In nano-water film. GAV-9 formed a bilayer structure, indicating that nano-water film can change the hydrophobicity of mica surface. These results help improve the transfer efficiency of peptides by using micro-contact printing method, and provide us a more intuitive understanding of the effect of temperature on the properties of water nano film. In the second part of the thesis,I have studied the effect of the solution conditions (including pH, ionic strength and so on) on the self-assembly process of a pentapeptide (NH2CO-KLV FF-NH2) on mica surface. And the results show that the pentapeptide self-assembly on mica surface is significantly affected by these solution conditions. For examples, pentapeptide only can perfectly self-assemble under the pH close to its isoelectric point, indicating that in this typical template-assisted self-assembly process, the solution pH affects the charge state of both peptides and the mica surface, thus determining whether the force between the template and the pentapeptide favor the occurrence of the self-assembly process. In fact, different cations show different effects on the template-assisted self-assembly process, which actually results from that both the charge state of mica surface and peptide are affected by the sizes and the charge numbers of the cations.