Structural function of C-terminal amidation of endomorphin
Structural function of C-terminal amidation of endomorphin
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DOI：
10.1111/j.1742-4658.2005.04919.x
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发表时间：
2005-10-01
期刊：
影响因子：
5.4
通讯作者：
Ishida, T
中科院分区：
文献类型：
--
作者：
In, Y;Minoura, K;Ishida, T
研究内吗啡肽-2 C-末端酰胺基的结构功能（EM2，H-Tyr-Pro-Phe-Phe-NH2），一种内源性μ-阿片受体配体，EM2及其C-末端游离酸的溶液构象（EM2OH，H-Tyr-Pro-Phe-Phe-OH）的TFE溶液采用二维核磁共振（2D H-1-NMR）测量和分子模拟计算相结合的方法，研究了三氟乙醇（trifluoroethanol）、水（pH 2.7和5.2）和十二烷基磷酸胆碱（DPC）水溶液胶束（pH 3.5和5.2）的动力学行为。两种肽在二甲亚砜、TFE和水中处于Tyr-Pro w键周围的顺式和反式旋转异构体之间的平衡，群体比为1：1至1：2，而它们主要在DPC胶束中吸收反式旋转异构体，除了在pH 5.2的EM2OH中，其反式/顺式旋转异构体比为2：1。50个可能的3D构象产生的每一个肽，采取不同的电子状态，这取决于溶剂的类型和pH值（中性和单阳离子形式的EM2，和两性离子和单价离子形式的EM2OH）的动态模拟退火方法，质子-质子距离的限制下，来自ROE交叉峰强度。根据骨架结构的构象模式，将这些构象异构体大致分为4组，即两个开放型（反向S（rS）型和数字7（n7）型）和两个折叠型（F1型和F2型）构象异构体。大多数EM2构象在中性（在TFE中）和单阳离子（在水和DPC胶束中）的形式采用开放结构（主要的RS型和次要的N7型构象的混合物），尽管反式/顺式旋转异构体的形式。另一方面，两性离子EM2OH在TFE、水和DPC胶束中表现出F1-和F2-型折叠构象的数量增加，其数量取决于它们的电子状态和pH值。这些折叠构象的大多数具有类似于由（Tyr 1）NH 3 +... COO-（Phe4），在其晶体结构中观察到。这些结果表明，羧基取代的C-末端酰胺基团，使肽结构更灵活，并导致折叠和开放构象的合奏。EM2的构象要求结合到μ-阿片受体和C-末端酰胺基团的结构功能的基础上，目前的构象特征的EM2和EM2OH和一个可能的模型结合到μ-阿片受体，从视紫红质的模板结构构建的基础上进行了讨论。
To investigate the structural function of the C-terminal amide group of endomorphin-2 (EM2, H-Tyr-Pro-Phe-Phe-NH2), an endogenous mu-opioid receptor ligand, the solution conformations of EM2 and its C-terminal free acid (EM2OH, H-Tyr-Pro-Phe-Phe-OH) in TFE (trifluoroethanol), water (pH 2.7 and 5.2), and aqueous DPC (dodecylphosphocholine) micelles (pH 3.5 and 5.2) were investigated by the combination of 2D H-1-NMR measurement and molecular modelling calculation. Both peptides were in equilibrium between the cis and trans rotamers around the Tyr-Pro w bond with population ratios of 1 : 1 to 1 : 2 in dimethyl sulfoxide, TFE and water, whereas they predominantly took the trans rotamer in DPC micelle, except in EM2OH at pH 5.2, which had a trans/cis rotamer ratio of 2 : 1. Fifty possible 3D conformers were generated for each peptide, taking different electronic states depending on the type of solvent and pH (neutral and monocationic forms for EM2, and zwitterionic and monocation forms for EM2OH) by the dynamical simulated annealing method, under the proton-proton distance constraints derived from the ROE cross-peak intensities. These conformers were then roughly classified into four groups of two open [reverse S (rS)- and numerical 7 (n7)-type] and two folded (F1- and F2-type) conformers according to the conformational pattern of the backbone structure. Most EM2 conformers in neutral (in TFE) and monocationic (in water and DPC micelles) forms adopted the open structure (mixture of major rS-type and minor n7-type conformers) despite the trans/cis rotamer form. On the other hand, the zwitterionic EM2OH in TFE, water and DPC micelles showed an increased population of F1- and F2-type folded conformers, the population of which varied depending on their electronic state and pH. Most of these folded conformers took an F1-type structure similar to that stabilized by an intramolecular hydrogen bond of (Tyr1)NH3+...COO-(Phe4), observed in its crystal structure. These results show that the substitution of a carboxyl group for the C-terminal amide group makes the peptide structure more flexible and leads to the ensemble of folded and open conformers. The conformational requirement of EM2 for binding to the mu-opioid receptor and the structural function of the C-terminal amide group are discussed on the basis of the present conformational features of EM2 and EM2OH and a possible model for binding to the mu-opioid receptor, constructed from the template structure of rhodopsin.