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標題: | 胺基酸側鏈長度的對角離子作用力對β-Hairpin 的影響 Effect of Amino Acid Side Chain Length on Diagonal Ion Pairing Interactions in a β-Hairpin |
作者: | Nian-Zhi Li 李念芷 |
指導教授: | 陳平 |
關鍵字: | β-hairpin,對角作用力,離子對作用力,膠原蛋白三螺旋,酵素,水膠, β-hairpin,diagonal interaction,ion pairing interaction,collagen triple helix,enzyme,hydrogel, |
出版年 : | 2018 |
學位: | 碩士 |
摘要: | β摺板是一種常見的蛋白質二級結構,其中β-hairpin是屬於β摺板最簡單的單元結構。在β摺板中相鄰兩股間常有異性電荷胺基酸的存在,顯示了離子對作用力的重要性。自然界中帶電荷胺基酸包括天冬胺酸、穀胺酸、精胺酸、賴胺酸,有趣的是他們側鏈上分別含有不同數目的亞甲基,構成側鏈長短的不同。在此研究中,我們利用β-hairpin作為模板,探討帶電荷胺基酸的側鏈長度在斜對角位置上對β-hairpin穩定度的影響,其中對角作用力的產生來自於β摺板的右手扭曲性質,可能使得空間上更加靠近。我們使用二維核磁共振技術來分析胜肽結構,利用化學位移的偏移程度獲知β-hairpin的折疊程度及其自由能,並進一步利用雙向改變循環分析方法探討是否存在斜對角的離子作用力,結果,只有側鏈長度最短的Asp-Agp離子對具有穩定β-hairpin的能力。可能原因來自側鏈較長的胺基酸具有較大的靈活度,增加亂度的影響,而較難在β-hairpin中產生穩定的作用,並且對Arg衍生物來說,側鏈的正電荷散布在胍基上,減弱了可能的跨股靜電作用力,所以更需要適合的長度配合產生對角離子作用力。重要的是,這些研究成果可以提供不同側鏈長度帶電荷胺基酸的相關資訊,輔助設計穩定的β摺板結構。
水膠是一種可以吸收大量水分而膨脹、能夠維持三維結構的材料。現有許多胜肽設計出來能進行自組裝形成水膠,例如:α螺旋、β摺板,然而膠原蛋白是哺乳類中含量最多的一種蛋白質,卻少有設計成功的例子存在。在此研究中,我們以已發表的文獻中能自組裝並構成水膠的膠原蛋白為基礎,設計出利用酵素來控制水膠形成的膠原蛋白三螺旋。我們透用圓二色光譜儀得到225奈米的特徵峰,確認為polyproline Ⅱ 螺旋的結構;在掃描式電子顯微鏡下呈現大範圍、相互連接的纖維結構;利用流變學研究水膠的應變和應力的關係,顯示設計出的水膠具有良好的強度。因此,這個利用酵素控制的水膠作為一種新的生物材料,可能會是個不錯的選擇。 β-Sheet is one of the major secondary structures in proteins. Oppositely charged amino acids are frequently observed across from one another on neighboring strands in β-sheets, implying the importance of ion pairing interactions. The natural charged amino acids Asp, Glu, Arg and Lys have different numbers of methylenes on the side chain. A β-hairpin was used as a model to investigate the effect of charged amino acid side chain length on diagonal cross-strand ion pairing interactions. The potential diagonal interaction might occur due to the right-handed twist of β-hairpins. The β-hairpin peptide structure was analyzed using 2D NMR methods (TOCSY, DQF-COSY, and ROESY). Chemical shift deviation data was used to determine the fraction folded and folding free energy. The potential diagonal ion-pairing interaction energy was derived from double mutant cycle analysis. Only the diagonal Asp-Agp interaction with the shortest side chain stabilized the β-hairpin. Residues with longer side chains displayed more flexibility and entropic penalty, and thus contributed little stabilizing energy to the β-hairpin. The diffuse positive charge on the guanidinium group might result in weaker electrostatics, leading to a greater need for diagonal interaction length matching. Importantly, these results could provide useful information for the design of stable β-sheet structures by using charges amino acids with different side chain lengths. Hydrogels are water-swollen materials which maintain a three-dimensional shape. Several α-helical and β-hairpin peptides have been designed to form self-assembling hydrogels. Collagen is the most abundant protein in mammals, but few designed collagen peptide materials exist. An enzyme-induced collagen triple helix hydrogel was designed based on a known self-assembly collagen hydrogel peptide. Hydrogel formed when the enzyme was applied. Circular dichroism spectra showed characteristics of polyproline Ⅱ helices with a maximum value around 225 nm. SEM images displayed the interconnected fibril structure corresponding to the gel properties. Rheological studies showed that the resulting hydrogel was rigid. The enzyme-induced hydrogel may be useful as novel biomaterials. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/77561 |
DOI: | 10.6342/NTU201802634 |
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顯示於系所單位: | 化學系 |
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