天門冬胺酸側鏈長度對α螺旋結構之影響及紫質固相合成

Abstract

自然界中帶電荷胺基酸帶有不同的側鏈長度。而帶電荷胺基酸能夠參與離子對作用力。離子對作用力可以穩定蛋白質結構。為了研究帶電荷胺基酸側鏈長度對於α螺旋構型穩定度的影響，一系列含有精胺酸以及天門冬胺酸衍生物的胜肽被合成出來。藉由CD光譜圖，測得每一條胜肽的α螺旋結構。由pH 7的數據得知，帶有越長側鏈的負電荷殘基(麩胺酸、天門冬胺酸)，帶有比越高的α螺旋結構。 紫質是一個被廣泛研究的大環。然而在現今的合成方法中遇到了許多困難。因合成過程中，容易發生polymerization、scrambling等副反應，而需要更進一步的純化。同樣的，合成帶有不同meso-位置取代基的紫質也較不容易。因此，我們希望利用固相合成改善現今紫質合成的問題。現在，我們已經成功利用Amino PEGA resin 合成出dipyrromethane。未來，如何將pyrrole chain延長以及環化，是需要更進一步研究的。

Natural charged amino acids have different side chain lengths. However, the effect of charged amino acid side chain length on protein stability remains unclear. Focusing on α-helices, intrahelical ion pairing interactions between charged amino acids can affect α-helix stability. To explore the effect of Arg and Asp side chain length on the helicity of peptides with intrahelical ion pairs, the following peptides were synthesized: ArgAsp3, ArgGlu3, AgpAsp4, AgpGlu4, AghAsp5, and AghGlu5. The peptides were synthesized by solid phase peptide synthesis and purified by RP-HPLC to over 98.5% purity. The helicity of the peptides were determined by circular dichroism (CD) spectroscopy at pH 2- 12. Based on the CD data at pH 7, the helicity of the peptides follow the trend ArgGlu3 > ArgAsp3, AgpGlu4 > AgpAsp4, AghGlu5 > AghAsp5. These results suggest that as the negatively charged residue side chain length increases, the peptide helicity increases. Porphyrins have been studied extensively but with low synthetic yield. To improve the synthetic process and yield, protocols for solid phase synthesis was developed. After many attempts, dipyrromethane, a precursor of porphyrin, was synthesized successfully by using amino PEGA resin and a new linker. Further work should focus on further chain lengthening and cyclization to form the porphyrin.