C末端殘基如何改變兩親性螺旋摺疊 : CD和NMR的研究

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Title:	C末端殘基如何改變兩親性螺旋摺疊 : CD和NMR的研究
Other Titles:	How C-terminal residue alters the helix folding of an amphipathic antimicrobial peptide : CD and NMR study
Authors:	曾雅琳;Tseng, Ya-Lin
Contributors:	淡江大學化學學系碩士班李長欣;Lee, Chang-Shin
Keywords:	C末端;兩親性;摺疊;CD;NMR;Folding;antimicrobial peptide;C-terminal
Date:	2014
Issue Date:	2015-05-04 09:48:16 (UTC+8)
Abstract:	如何從蛋白質序列摺疊成其獨特的三維結構，一直是重要的研究課題之一。在其他文獻報告指出，蛋白質的C末端殘基會影響蛋白質的摺疊行為。由於蛋白質的胺基酸數目較多，實驗的複雜性較高，為了降低實驗的複雜性，此論文中選用胺基酸數目較少的MP-B胜肽(14個胺基酸)及其衍生物，將其溶於30% TFE的水溶液中，溫度為310 K，利用CD和NMR進行研究，觀察胜肽的C末端殘基對於蛋白質摺疊行為的影響。從CD實驗中說明，MP-B及其衍生物在30% TFE溶液中會形成α-helix結構。利用不同溫度的DOSY實驗觀察MP-B及其衍生物的疏水性與寡聚體之間的關係，並討論寡聚狀態的熱穩定性。從抗菌活性實驗的結果發現MP-B及其衍生物的抗菌效果為MP-B > MP-BL15 > MP-B1-13。將MP-B及其衍生物的NOE距離限制放入結構計算中，統計每條胜肽的100個螺旋摺疊結構，並探討C末端對於摺疊結構熱穩定性的重要性。統合所有的實驗結果，當胜肽C末端無序的殘基無法提供足夠的熵時，會以螺旋N端展開的方式來增加熵。胜肽具有較穩定的結構和寡聚狀態時，會有較佳的抗菌活性，因此，如欲設計一個具有抗菌活性的胜肽，其C末端殘基的作用具有很關鍵的影響。 One of the most interesting questions in biophysics is how protein sequences determine their unique three-dimensional structure. Previous studies reported that the residues at C-terminal can have effects on the protein folding behaviors. Since a large protein is highly complex, for simplicity, in this study we use MP-B (14 amino acids) and its analogues in 30% TFE-d3 aqueous solution as a model system. By using circular dichroism (CD) and NMR methods, we can get insight into how the C-terminal segment may influence the folding behavior of proteins. Spectra of CD indicated that our peptides may form α-helical conformations in 30%TFE. Oligomerization and thermal stability of peptides were investigated by performing diffusional experiments with variable temperatures. The antimicrobial activity of MP-B1-13, MP-B and MP-BL15, is ordered as MP-B > MP-BL15 > MP-B1-13. 100 of structures of different kind foldings were calculated with NMR data to investigate the effects of C-terminal segment on folding. Our results suggested that while the disordered residues at C-terminal can’t provide enough motional entropy, the helical N-terminal may be partially unfolded to increase the entropy. When peptides have more stable structure and oligomeric state, they may have greater antimicrobial activity. The results implied the disordered C-terminal residues may play a critical role for the structure and activity of a peptide. The knowledge is especially important while a peptide segment is designed or truncated for studies of structure and function.
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