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標題: | 抑制雞蛋白溶菌酶之類澱粉纖維形成 Inhibition of Amyloid Fibril Formation of Hen Egg White Lysozyme |
作者: | Su-Chun How 侯素君 |
指導教授: | 王勝仕(Sheng-Shih Wang) |
關鍵字: | 類澱粉纖維,雞蛋白溶菌?,抑制,小分子, Amyloid fibril,hen egg white lysozyme,inhibition,small molecule, |
出版年 : | 2019 |
學位: | 博士 |
摘要: | 類澱粉纖維之形成是幾種不同退行性人類疾病的關鍵病理學特徵。有證據表明,澱粉樣蛋白原纖維緩解/抑制被認為是治療這些疾病的有希望的方法。然而,目前尚未有任一抑制劑或緩解劑可以達成此一目標。
在本研究中吾人使用雞蛋白溶菌酶來當作蛋白質模型,其原因主要歸因於其結構與人類溶菌酶序列相似性很高,且形成之類澱粉纖維結構也與之十分類似,再加上人類溶菌酶被認為是導致全身性之類澱粉沉積症有關。因此吾人透過研究雞蛋白溶菌酶纖維化之過程,可以幫助了解如何抑制類澱粉蛋白之纖維化。 本研究使用了三種不同之小分子抑制劑,分別為固綠FCF、亞甲基藍,及亮藍G。其中固綠FCF與亮藍G 兩者皆為三苯甲烷類之染料。其中固綠FCF已被美國食品藥品管理局(FDA)核可作為食用色素;而亮藍G則已被證實為安全且可以通過血腦屏障之小分子。至於亞甲基藍則是吩噻嗪家族化合物,由於其不具毒性也無其它副作用,因此被用作治療各種癌症及非癌症之藥物。除此之外,亞甲基藍已證實為一種具有潛力治療阿茲海默症之藥物。 這裡吾人利用不同之分析方法,包含自身螢光、ThT螢光、ANS螢光、電子穿透顯微鏡及圓二色光譜儀等,分別探討固綠FCF、亞甲基藍及亮藍G三種染劑對於雞蛋白溶菌酶形成類澱粉纖維之影響。ThT螢光強度結果顯示固綠FCF(25%)及亮藍G(32.8%)與亞甲基藍(1:1.11以下螢光強度沒有明顯之變化)相較具有較佳抑制類澱粉纖維形成之效果。而固綠FCF與亮藍G之圓二色光譜儀之結果卻有些許不同,固綠FCF抑制了β-摺板結構的形成;而亮藍G則依舊維持了相若之β-摺板結構之量。此結果表明亮藍G並無法降低類澱粉纖維之量。而由TEM之結果卻可以發現亮藍G使形成之類澱粉纖維變短。因此可以推測亮藍G抑制類澱粉纖維之機制為誘導蛋白質形成較短之纖維。但因為形成之纖維量與未添加小分子之蛋白質相若,故可以保留較多之原態蛋白質於樣品中。蛋白質電泳結果證實了這點。 本研究之結果顯示影響蛋白質形成類澱粉纖維之主要機制為小分子藉由與疏水胺基酸之交互作用,進而阻礙了蛋白質疏水區之裸露。而具有硫酸根之分子(亮藍G與固綠FCF)因會與蛋白質產生靜電作用力,因而提升了抑制蛋白質纖維化之能力。而亮藍G與固綠FCF之不同在於亮藍G所帶之負電較少,且苯環上多了兩個甲基,因而影響蛋白質形成較短之類澱粉纖維。 綜合以上結果得知小分子之結構、大小、官能基之種類皆會影響類蛋白質類澱粉纖維化。而吾人希望藉由探討小分子對蛋白質類澱粉纖維化之影響,能對發展治療類澱粉纖維症之藥物有些許之幫助。 Amyloid fibril formation serves as a key pathological feature of several different human degenerative diseases. Evidence suggests that mitigation/inhibition of amyloid fibril formation is considered a promising approach toward treating these diseases. However, as of now, there has been no effective small molecule available to cure amyloid diseases. The reasons why hen egg white lysozyme was used as the model protein in this research work are as follows: (1) hen egg white lysozyme is structurally homologous to human lysozyme, which is the protein associated with hereditary systemic amyloidosis, and (2) its fibrils were found to resemble the fibrillar species of human lysozyme. Investigation of amyloid fibril formation using hen egg white lysozyme can aid in a better understanding of the possible inhibition strategies for tackling amyloid aggregation. In our study, we used three kinds of small molecules including fast green FCF, methylene blue, and brilliant blue G. Both fast green FCF and brilliant blue G are triarylmethane dyes, fast green FCF is approved by the FDA as a food dye, while brilliant blue G has been shown to be safe with good blood–brain-barrier-permeability. Methylene blue, a compound belonging to the phenothiazinium family, has the potential to treat a variety of cancerous and non-cancerous diseases with low toxicity and minimal side effects. Furthermore, evidence demonstrates that methylene blue may be a promising molecules for the treatment of Alzheimer’s disease. Here, we examine the effects of fast green FCF, methylene blue and brilliant blue G on amyloid fibril formation derived from hen egg white lysozyme using a variety of spectroscopic techniques, such as intrinsic fluorescence, ANS fluorescence and ThT fluorescence assays, transmission electron microscopy, and circular dichroism spectroscopy. ThT fluorescence intensity results show that fast green FCF(25%) and brilliant blue G(32.8%) possess better inhibition efficacy than methylene blue (below 1:1.11,ThT intensity has no significant change). However, CD results reveal that fast green FCF and brilliant blue G affect hen egg white lysozyme differently. The addition of fast green FCF was observed to reduce the β-sheet secondary structure content associated with amyloid fibrillogenesis, which was not found in the case of brilliant blue G. Our results demonstrate that the addition of brilliant blue G is not able to suppress the amyloid fibril-forming propensity of lysozyme but only shorten the length of fibrillary species. Moreover, our SDS-PAGE results suggest that more native proteins are retained in the sample. In addition, our results further suggest that the observed inhibitory actions against amyloid fibril formation is mainly correlated with the interaction between the small molecules and protein hydrophobic sites. Given that both fast green FCF and brilliant blue G have sulfonate functional groups, the two molecules are able to electrostatically interact with the protein, thus further mitigating amyloid fibril formation. In addition, we surmise that the less negative charge and two additional methyl groups attached to the triphenylmethane structure might account for why the presence of brilliant blue G induces the formation of shorter fibrils, but can not suppress amyloid fibrillogenesis. Taken together, we conclude that small molecules’ inhibitory activity toward amyloid fibril formation is dependent upon the structure, size, and types of functional groups attached to them. We believe exploring the effects of small molecule on amyloid fibrillogenesis of lysozyme can contribute to the development of drugs for the treatment of amyloid diseases. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/21750 |
DOI: | 10.6342/NTU201900613 |
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顯示於系所單位: | 化學工程學系 |
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