麩胺酸側鏈長度於螺旋內離子對作用力的影響以及離胺酸側鏈長度和胺基酸位置對螺旋程度的影響

蛋白質超過30%結構含有α螺旋結構。Lifson-Roig理論是一個用來描述胜肽的螺旋結構多寡的理論，其假設每個胺基酸形成螺旋的傾向不受胺基酸所在的位置影響。為了驗證這個假設，我們合成了一系列的胜肽，利用圓二色光譜儀測量此系列胜肽的螺旋程度，並且將胺基酸在6, 11和16號位置的w值求出。在6號和11號位置的w值很相近，但16號位置的w值卻非常的高。為了探討胺基酸側鏈長短對w值的影響，我們利用固相胜肽合成技術設計並合成一系列含有精氨酸長度不同的非自然界胺基酸S-2-amino-6-guanidinohexanoic acid (Agh),S-2-amino-4-guanidino-butyric acid (Agb), S-2-amino-3-guanidinopropionic acid (Agp)和離氨酸長度不同的非自然界胺基酸Ornithine (Orn), S-2,4-diaminobutyric acid (Dab), S-2,3-diaminopropionic acid (Dap)並根據修飾過的 Lifson-Roig理論測量其w值。在精氨酸長度不同的非自然界胺基酸中，精氨酸的w值最高，顯示精氨酸形成螺旋的傾向最高。在離氨酸長度不同的非自然界胺基酸中，w值隨著側鏈長度增長而增加。螺旋內離子對作用力可以穩定結構．側鏈長度與正負電荷相對間距會影響螺旋程度．為了研究側鏈長度對於影響程度的影響，利用固相胜肽合成技術合成並設計一系列含有合成出與精氨酸長度不同的非自然界胺基酸S-2-amino-6-guanidinohexanoic acid (Agh),S-2-amino-4-guanidino-butyric acid (Agb), S-2-amino-3-guanidinopropionic acid (Agp)以及與穀胺酸長度不同的天門冬胺酸的胜肽序列，包括AspAgh4, GluAgh4, AspAgb3, GluAgb3, AgpAsp5以及 AgpGlu5. 利用圓二色光譜儀測量不同胜肽在pH 2-12範圍下的螺旋程度。圓二色光譜儀測得訊號結果包括個別胺基酸本身對於螺旋喜好程度、胺基酸序列中側鏈之間與的作用力以及胺基酸側鏈與螺旋骨架N端C端作用力．本研究中，根據圓二色光譜儀訊號顯示pH 7情況下，螺旋程度大小依序為GluAgh4 > AspAgh4, GluAgb3 > AspAgb3, AgpGlu5 > AgpAsp5. 當負電荷胺基酸側鏈越長，其表現出的螺旋程度也相對較高。

關鍵字

α螺旋；胺基酸側鏈；離子對作用力；固相胜肽合成

並列摘要

One third of all protein residues adopt a helical conformation. Statistical mechanical models such as modified Lifson-Roig theory are used to describe the conformational ensemble of monomeric helical peptides. One basic assumption in these statistical models is that the helix propensity for a given amino acid is position independent. To test this assumption, the helix propensity for neutral non-Ala residues at various guest positions were derived from circular dichroism spectroscopy (CD) data. Helix propensities were similar for positions 6 and 11 for the same amino acid, but much higher at position 16. Helix propensity (w) for Arg and Lys analogs were derived based on modified Lifson-Roig theory to investigate the effect of Lys and Arg side chain length on helix formation. The helix propensity (w) for Arg analogs followed the trend: wArg > wAgh > wAgb > wAgp, indicating the uniqueness of the Arg side chain length in helix formation. In contrast, all three Lys analogs were energetically unfavorable for N-capping. Orn and Dap were energetically favorable for C-capping, whereas Dab was energetically unfavorable for C-capping. All three Lys analogs were energetically unfavorable at internal helix positions. Electrostatic ion pairing interactions between oppositely charged amino acids can stabilize proteins and helical structures. To study the effect of Glu side chain length and relative spacing on intrahelical ion pairing interaction, peptides AspAgh4, GluAgh4, AspAgb3, GluAgb3, AgpAsp5, and AgpGlu5 were synthesized and studied by CD at pH 2-12. Based on CD data at pH 7, the helical content of the peptides followed the trend GluAgh4 > AspAgh4, GluAgb3 > AspAgb3 and AgpGlu5 > AgpAsp5. The results showed that helicity increases with increasing side chain length of the negatively charged residue (Glu vs Asp).

並列關鍵字

α-helix ； helix propensity ； solid phase peptide synthesis ； amino acid side chain ； ion-pairing interaction

參考文獻

1. Gavin, A. C.; Aloy, P.; Grandi, P.; Krause, R.; Boesche, M.; Marzioch, M.; Rau, C.; Jensen, L. J.; Bastuck, S.; Dumpelfeld, B.; Edelmann, A.; Heurtier, M. A.; Hoffman, V.; Hoefert, C.; Klein, K.; Hudak, M.; Michon, A. M.; Schelder, M.; Schirle, M.; Remor, M.; Rudi, T.; Hooper, S.; Bauer, A.; Bouwmeester, T.; Casari, G.; Drewes, G.; Neubauer, G.; Rick, J. M.; Kuster, B.; Bork, P.; Russell, R. B.; Superti-Furga, G. Proteome survey reveals modularity of the yeast cell machinery. Nature 2006, 440, 631-636.