- 學位論文
以核磁共振光譜技術探討Octreotide與SDS微胞作用之性質
Octreotide-micelle interactions via NMR spectroscopy
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摘要
本文探討由八個胺基酸所組成之環狀胜肽Octreotide (SMS 201-995) D-Phe1-cyclo[Cys2-Phe3-D-Trp4-Lys5-Thr6-Cys7]-Thr8-ol，Octreotide穿過細胞膜並與體制素受體鍵結而具有類似體制素之生化活性，特別是對體制素受體SSTR-2/3/5具選擇性位於腦、下丘腦及垂體已被確定。藉由螢光實驗證實Octreotide進入SDS ( Sodium Dodecyl Sulfate )微胞溶液其色胺酸殘基位於微胞厭水性環境中，並以脈衝磁場梯度實驗可分別測量Octreotide 於水溶液及SDS微胞環境中之擴散係數，進而估計Octreotide 與SDS微胞之鍵結常數為 6.12×102 M-1，由自由能公式得△G為 -15.9 kJ/mol 顯示Octreotide 與SDS微胞之鍵結作用為自發性結合，與螢光實驗相符合。最後使用核磁共振光譜技術及分子模擬研究Octreotide之構型特徵，並根據化學位移特性、NOE及耦合常數3JNH-CαH之分析顯示，Octreotide於SDS微胞溶液環境下構型呈現β-迴路和螺旋結構(碳端310-helix)之平衡狀態，且D-W4、K5為β-迴路之中心。Octreotide之構型與芳香環支鏈的空間關係以及其對體制素受體選擇性之影響在文中進一步的討論。
並列摘要
This paper studies a conformational of an octapeptide D-Phe1-cyclo[Cys2-Phe3-D-Trp4-Lys5-Thr6-Cys7]-Thr8-ol (disulfide bridged), known as Octreotide (or SMS 201-995 or sandostatin) using nuclear magnetic resonance spectroscopy and molecular modeling method. Octreotide displays both somatostatin-like and opioid-like bioactivities which colud be mediated through trans-membrane receptors SSTRs. Predominant selectivity to SSTR2、SSTR3、SSTR5 located in brain, hypothalamus and pituitary has been identified for Octreotide. The interaction between Octreotide and SDS micelle is also monitored by the blue shift and attenuation of fluorescence signal of peptide upon the introduction of micelle. The association constant of Octreotide-micelle complex is estimated by a two-state approximation based on the diffusion coefficients, measured by PFG-NMR spectroscopy, for Octreotide in aqueous and micellar solutions, respectively. The binding constant is about 6.12×102 M-1. These results are evidences to show that the tryptophan residue locates in the hydrophobic environment of the micelle and the which are consistent with the observation in NMR experiments. Base on the analysis of chemical shift deviation, NOE cross-peaks and coupling constants, the backbone conformation of Octreotide, under micellar environment, was in equilibrium between β-strand and helix-like secondary structure fold, with a β-turn centered at D-Trp4-Lys5. The correlation between the relative positions of the aromatic side-chain of the peptide and its receptor affinity is further discussed.
參考文獻
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