膠原蛋白為動物體含量最多的蛋白質，主要分布於骨骼、皮膚與細胞組織中，其基底結構為三條具備聚脯胺酸第二型結構( PPII )的胜肽鏈以右旋方式纏繞而成的三股螺旋，其中每條胜肽鏈再以Xaa-Yaa-Gly之方式組成。穩定三股螺旋結構的作用力於許多文獻皆曾探討，其中靜電交互作用也不乏被設計於序列中以增強結構的穩定效果，因此本研究探討此作用力對三股螺旋結構穩定性之影響，並針對末端點靜電作用力對結構影響進行一系列的討論。
研究實驗中，我們以Gly-Gly-(Pro-Hyp-Gly)7-Gly-Gly作為原生型胜肽，並將末端的胺基酸分別置換為Lys與Glu以分析靜電交互作用對結構的影響。我們發現當碳端Gly置換為Lys時，藉由其側鏈上帶正電荷之胺基與末端羧基所產生的靜電吸引力可使結構提升穩定性，相反地，氮端Glu的置換則較無顯著的影響；當Lys與Glu分別置換在氮端以及碳端時，則會因為電荷間的排斥力效應使得結構穩定性下降。此外，我們也將胜肽溶入高濃度的NaCl溶液中，藉由離子的遮蔽效應再次證實靜電交互作用力的存在。
接著，我們進一步將帶電荷胺基酸之側鏈長度縮短，以觀察側鏈長度對於作用力大小的影響。實驗結果發現僅有同區域存在羧基之胜肽產生靜電排斥現象，其餘胜肽皆無此效應，因此我們推測當側鏈縮短時，作用距離存在限制性，因而帶電荷官能基的作用範圍成為重要的影響因子。

Collagen, the primary protein in mammals, is abundant among bones, skins and connective tissues. The single strand of native collagen adopts the polyproline II ( PPII ) structure and consists of the repeating tripeptide Xaa-Yaa-Gly. Three PPII strands then form the collagen basic structure, generally known as triple helices. From the previous studies, various interactions have been utilized to improve the stability of a collagen triple helix. Here we focused on the study of electrostatic interactions on collagen triple helices.
In this study, we explored the contribution of terminal charge charge interactions to the triple helix stability. We designed Gly Gly-(Pro-Hyp-Gly)7-Gly-Gly as a parent peptide and incorporated Lys or Glu into the terminus to examine the effects of terminal electrostatic interactions on the triple helix stability. We found that incorporating Lys into the C-terminus of a peptide generates the electrostatic attractions between its side chain and the terminal carboxylic group to stabilize the triple helix. While installing Glu into the N-terminus of a peptide only introduces a relatively small stabilization effect. In contrast, incorporating Lys into the N-terminus or Glu to the C-terminus destabilizes the triple helix because of the charge-charge repulsions. Such effects were further confirmed by the experiments with concentrated salts present, which the electrostatic interactions are shielded by the salts in solution.
In addition, we also analyzed the relationship between the length of the side chains and the electrostatic interactions. Surprisingly, the results revealed that only Asp induced larger charge-charge repulsions to further destabilize the triple helix. The results suggest that the size of the charged functional groups may play a critical role affecting the interactions.

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