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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Populations of the three major backbone conformations in 19 amino acid dipeptides
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Populations of the three major backbone conformations in 19 amino acid dipeptides

机译：19个氨基酸二肽中三个主要骨架构象的种群

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摘要

The amide III region of the peptide infrared and Raman spectra has been used to determine the relative populations of the three major backbone conformations (P_II β, andα_R) in 19 amino acid dipeptides. The results provide a benchmark for force field or other methods of predicting backbone conformations in flexible peptides. There are three resolvable backbone bands in the amide III region. The major population is either P_II or |i for all dipeptides except Gly, whereas the α_R population is measurable but always minor (≤10%) for 18 dipeptides. (The Gly φ，ψ map is complex and so is the interpretation of the amide III bands of Gly.) There are substantial differences in the relative p and P_II populations among the 19 dipeptides. The band frequencies have been assigned as P_II, 1,317-1,306 cm~-1; α_R, 1,304-1,294 cm-1; and β, 1,294-1,270 cm~-1. The three bands were measured by both attenuated total reflection spectroscopy and by Raman spectroscopy. Consistent results, both for band frequency and relative population, were obtained by both spectroscopic methods. The β and P_II bands were assigned from the dependence of the ~3J(H_N,H_α) coupling constant (known for all 19 dipeptides) on the relative p population. The P_II band assignment agrees with one made earlier from Raman optical activity data. The temperature dependences of the relative p and P_II populations fit the standard model with Boltzmann-weighted energies for alanine and leucine between 30 and 60℃.
机译：肽红外和拉曼光谱的酰胺III区已用于确定19个氨基酸二肽中三个主要骨架构象（P_IIβ和α_R）的相对种群。结果为力场或预测柔性肽中骨架构象的其他方法提供了基准。在酰胺III区域中存在三个可分辨的主链。除Gly以外，所有二肽的主要种群是P_II或| i，而18个二肽的α_R种群是可测量的，但总是次要的（≤10％）。 （Glyφ，ψ映射很复杂，Gly的酰胺III谱带的解释也很复杂。）19个二肽之间的相对p和P_II群体存在很大差异。频带频率已指定为P_II，1,317-1,306 cm〜-1; α_R，1,304-1,294 cm-1; β为1,294-1,270 cm〜-1。通过衰减全反射光谱法和拉曼光谱法测量这三个谱带。两种光谱方法均获得了频带频率和相对种群的一致结果。根据〜3J（H_N，H_α）耦合常数（所有19个二肽均已知）对相对p群体的依赖关系来分配β和P_II谱带。 P_II波段分配与先前从拉曼光学活动数据得出的分配一致。 p和P_II相对种群的温度依赖性符合标准模型，其中丙氨酸和亮氨酸的玻尔兹曼加权能量在30至60℃之间。

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