Inhibition of Amyloid Fibril Formation of Hen Egg White Lysozyme

• Main Authors: Su-Chun How, 侯素君
• Other Authors: Sheng-Shih Wang
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/zeu3kb

博士 === 國立臺灣大學 === 化學工程學研究所 === 107 === 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.