Cation-π 作用力對膠原蛋白穩定性及自組裝影響之探討

Study of Cation-π interactions in the stability and self-assembly of collagen triple helix

陳佳青(Chia-Ching Chen)

指導教授 ： 洪嘉呈

國立清華大學/理學院/化學系/碩士(2010年)

摘要

膠原蛋白的結構是由三條左旋第二型聚脯胺酸螺旋結構，沿著一個相同的主軸右旋轉組成，序列中每三個胺基酸有一個 Gly 、高含量的亞胺基酸和氫鍵是促進其穩定性的重要因素。另一方面， 正電荷與芳香環四極矩間的非共價鍵作用力 - cation-π 作用力，也陸續被發現其在蛋白質的 ligand 鍵結等生物辨識上的重要性。因此，我們利用一系列的主客胜系統去探討 cation-π 作用力對膠原蛋白三股螺旋的影響；我們合成了一系列胜： Ac-(POG)3-(PYGXOG)-(POG)3-NH2 ，在 X 位置為 Phe、 Tyr 、 Trp 、 Phe(4-F), 、 Phe(F5) 和 Phe(4-Me)； Y 位置為 Lys 、 Arg。 而 X 位置的 Trp 由於其立體障礙的緣故，使其形成 cation-π 作用力不如預期的大。而當 Y 位置為 Arg 的 Tm 值比 Lys 時高，因為 Arg 側鏈形狀的幾何特性，所以比 Lys 易產生 cation-π 作用力，與之前的文獻結論一致。此外，非自然胺基酸取代則顯現出，當芳香環側鏈上有電子基的去活化者 – 氟，會減少膠原蛋白模擬胜的穩定性，因其降低 π 電子密度而減弱了 cation-π 作用力，證實 cation-π 作用力對於膠原蛋白三股螺旋的穩定性有重要的貢獻。
更進一步，我們設計膠原蛋白模擬胜序列： Ac-RG(POG)8F-NH2 和 Ac-RG(POG)10F-NH2 ，發現 cation-π 作用力對促進膠原蛋白模擬胜的自組裝速率的影響。最後，我們亦試著利用 cation-π 作用力去形成異源三聚體膠原蛋白模擬胜。
以上這些結果顯示出，強健的非共價鍵作用力 – cation-π 作用力，可以被應用在穩定膠原蛋白模擬胜，及促使膠原蛋白模擬胜自組裝成高階結構。
Collagen is a right-handed triple helix composed of three left-handed PPⅡ helices. The presence of Gly as every third residue, a high content of imino acids and hydrogen bonding are significant characteristics to improve the stability of collagen. Cation-π interactions are considered as an electrostatic attraction between a positive charge and the quadrupole moment of the aromatic ring and are important in a variety of proteins that bind to ligands or substrates. Here, we used a host-guest peptide system to study the cation-π interactions in the collagen triple helix. A series of Ac-(POG)3-(PYGXOG)-(POG)3-NH2 peptides were synthesized and characterized, where X is Phe, Tyr, Trp, Phe(4-F), Phe(F5), Phe(4-Me), and Y is Lys, Arg. Owing to the steric hindrance, the cation-π interactions formed by Trp are not as stable as what we predicted. The peptides with Arg in the Y position have a higher Tm value than those with Lys at this position consistent with the previous conclusion that Arg is more likely than Lys to be in a cation-π interaction due to its geometric features. Moreover, the unnatural residue substitutions showed that an electron-withdrawing deactivator, fluorine, in the aromatic ring will reduce the thermal stability because it would reduce the π-electron density as well as the cation-π interaction. These results suggest that cation-π interactions significantly contribute to the collagen triple helix stability.
Furthermore, we design another two peptides, Ac-RG(POG)8F-NH2 and Ac-RG(POG)10F-NH2 to promote the rate of self-assembly by cation-π interactions. We have also tried to use cation-π interactions to form the heterotrimeric collagen helices. These results exhibit that the strong and non-covalent force, cation-π interactions, could be applied to stabilize collagen triple helices and assemble them into a higher order structure.

關鍵字

Cation-π 作用力 ； 膠原蛋白 ； 自組裝

並列摘要

無資料

並列關鍵字

Cation-π interactions ； collagen ； self-assembly

參考文獻

2. Dougherty, D. A. Science 1996, 271, 163.

3. Scrutton, N. S., Raine, A. R. C. Biochem. J. 1996, 319, 1.

7. Prockop, D. J., Kivirriko, K. I. Ann. Rev. Biochem. 1995, 64, 403.

8. Prockop, D. J. Matrix Biol. 1998, 16, 519.

9. Prockop, D. J. Biochem. Soc. Trans. 1999, 27, 15.