Augspurger J D, Bindra V A, Scheraga H A, Kuki A
Baker Laboratory of Chemistry, Cornell University, Ithaca, New York 14853-1301.
Biochemistry. 1995 Feb 28;34(8):2566-76. doi: 10.1021/bi00008a022.
1D and 2D NMR spectroscopy is used to determine the helical stability of two Aib-rich peptides, iBoc-(Aib)3-DkNap-Leu-Aib-Ala-(Aib)2-NH(CH2)2OCH3 (Dk4[7/9]) and Ac-(Aib)2-beta-(1'-naphthyl)Ala-(Aib)2-Phe-(Aib)2-NHMe (Nap3Phe6[6/8]), where the bracket notation indicates the number of Aib-class residues/total number of residues. 2D ROESY experiments, carried out previously on Nap3Phe6[6/8] in DMSO (Basu & Kuki, 1993), showed that this compound adopts the 3(10)-helical conformation at 20 degrees C. The first step in the present work is to apply this technique to the peptide Dk4[7/9], demonstrating that it likewise adopts the 3(10)-helical conformation in chloroform at 20 degrees C. The amide proton shifts of Nap3-Phe6[6/8] in DMSO and Dk4[7/9] in C2D2Cl4 were then monitored by means of 1D NMR over a large temperature range, up to 150 and 120 degrees C, respectively. The nonamer Dk4[7/9] exhibits no evidence of any conformational or unfolding transition as the temperature is raised. The nearly temperature independent amide proton chemical shifts of this nonamer are an indication of retention of the intrahelical hydrogen bonding, which was then verified directly by solvent perturbation with DMSO at 120 degrees C. The resulting hydrogen-bonding pattern confirms that Dk4[7/9] retains its 3(10)-helical conformation in C2D2Cl4 over the entire temperature range. This conformational quietness is exploited to examine the intrinsic temperature dependence of free versus intrahelically hydrogen bonded amide proton shifts within the same peptide structure. It is also shown that Nap3Phe6[6/8] retains its 3(10)-helical conformation over the entire temperature range in the stronger hydrogen-bonding solvent DMSO. The extreme thermal stability of these octameric and nonameric Aib-rich peptides in both solvents is contrasted with that of much longer alanine-rich peptides in water.
一维和二维核磁共振光谱用于确定两种富含Aib的肽的螺旋稳定性，即iBoc-(Aib)3-DkNap-Leu-Aib-Ala-(Aib)2-NH(CH2)2OCH3（Dk4[7/9]）和Ac-(Aib)2-β-(1'-萘基)Ala-(Aib)2-Phe-(Aib)2-NHMe（Nap3Phe6[6/8]），其中括号表示Aib类残基的数量/总残基数量。先前在DMSO中对Nap3Phe6[6/8]进行的二维ROESY实验（Basu和Kuki，1993年）表明，该化合物在20℃时采用3(10)-螺旋构象。本工作的第一步是将该技术应用于肽Dk4[7/9]，证明它在20℃的氯仿中同样采用3(10)-螺旋构象。然后通过一维核磁共振在高达150℃和120℃的大温度范围内监测DMSO中的Nap3-Phe6[6/8]和C2D2Cl4中的Dk4[7/9]的酰胺质子位移。随着温度升高，九聚体Dk4[7/9]没有显示出任何构象或解折叠转变的迹象。该九聚体几乎与温度无关的酰胺质子化学位移表明螺旋内氢键得以保留，随后在120℃用DMSO进行溶剂扰动直接验证了这一点。所得的氢键模式证实Dk4[7/9]在整个温度范围内在C2D2Cl4中保持其3(10)-螺旋构象。利用这种构象稳定性来研究同一肽结构中游离与螺旋内氢键结合的酰胺质子位移的内在温度依赖性。还表明Nap3Phe6[6/8]在更强的氢键溶剂DMSO中在整个温度范围内保持其3(10)-螺旋构象。将这些八聚体和九聚体富含Aib的肽在两种溶剂中的极端热稳定性与水中长得多的富含丙氨酸的肽的热稳定性进行了对比。
