Carpenter K A, Wilkes B C, Weltrowska G, Schiller P W
Laboratory of Chemical Biology and Peptide Research, Clinical Research Institute of Montreal, Canada.
Eur J Biochem. 1996 Nov 1;241(3):756-64. doi: 10.1111/j.1432-1033.1996.00756.x.
The conformational properties of three Tyr-Tic-NH-R dipeptide analogs [where R = (CH2)2-Ph, (CH2)3-Ph or (CH2)2-cHx; Ph = phenyl; cHx = cyclohexyl and Tic = tetrahydroisoquinoline-3-carboxylic acid] have been investigated in purely aqueous solution and in the presence of fully deuterated dodecylphosphocholine micelles. H-Tyr-Tic-NH-(CH2)2-Ph is an opioid delta-agonist, whereas H-Tyr-Tic-NH-(CH2)3-Ph is a fairly potent delta-antagonist. H-Tyr-Tic-NH-(CH2)2-cHx is a less potent delta-antagonist. 1H-NMR spectra revealed that conformers containing cis and trans configurations of the Tyr-Tic peptide bond were present in all compounds in H2O and the H2O/lipid solvent. Analyses of the NMR data for the compounds in H2O indicate that in all three dipeptides the C-terminal substituent is flexible and the Tyr-side-chain adopts a trans orientation in most of the conformations. This promotes a compact Tyr-Tic structure. NOE patterns observed for the compounds in the micelle solution indicate that Tyr has an even greater tendency to assume a trans side chain configuration in the biphasic-solvent system. This feature was more pronounced in the trans conformers than in the cis conformers. Specific lipid-peptide interactions were indicated by NOESY spectra acquired for micelle samples incorporating 20% (by mass) protonated lipid. According to the obtained NOE data, Tyr and Tic form an aromatic cluster which preferentially inserts into the lipid interior of the micelle for the trans conformers of all three dipeptides and for the cis conformer of H-Tyr-Tic-NH-(CH2)2-Ph. For the cis isomers, partitioning of the C-terminal substituents into the lipid phase exhibited more diverse behaviour. The cis conformers of H-Tyr-Tic-NH-(CH2)3-Ph and H-Tyr-Tic-NH-(CH2)2-cHx preferentially anchor to the micelle via their C-terminal substituent, while the corresponding region in H-Tyr-Tic-NH-(CH2)2-Ph remains flexible and immersed in the aqueous phase. The inconsistent mode of peptide-micelle interaction observed for cis conformers of the three compounds studied is explained in terms of differences in their dipeptide-substituent hydrophobicities. The more apolar the substituent, the greater its tendency to preferentially insert into the lipid core of the micelle. Amide-proton temperature coefficients measured for the three peptides revealed differences amongst the cis and trans isomers. The amide proton in the trans conformer of each compound is highly exposed to the aqueous phase in both solvent systems studied, whereas the cis NH proton of each peptide is only partially exposed. These results demonstrate that a subtle structural modification of an active peptide analog can result in dramatic changes of its biological activity and its mode of partitioning at a membrane surface.
研究了三种Tyr-Tic-NH-R二肽类似物[其中R = (CH2)2-Ph、(CH2)3-Ph或(CH2)2-cHx；Ph = 苯基；cHx = 环己基，Tic = 四氢异喹啉-3-羧酸]在纯水溶液以及存在全氘代十二烷基磷酸胆碱胶束的情况下的构象性质。H-Tyr-Tic-NH-(CH2)2-Ph是一种阿片δ激动剂，而H-Tyr-Tic-NH-(CH2)3-Ph是一种相当强效的δ拮抗剂。H-Tyr-Tic-NH-(CH2)2-cHx是一种效力较弱的δ拮抗剂。1H-NMR光谱显示，在H2O和H2O/脂质溶剂中的所有化合物中均存在含有Tyr-Tic肽键顺式和反式构型的构象异构体。对H2O中化合物的NMR数据进行分析表明，在所有三种二肽中，C端取代基具有柔性，并且在大多数构象中Tyr侧链呈反式取向。这促进了紧凑的Tyr-Tic结构。在胶束溶液中观察到的化合物的NOE模式表明，在双相溶剂体系中Tyr更倾向于呈现反式侧链构型。这一特征在反式构象异构体中比在顺式构象异构体中更为明显。对于含有20%（质量）质子化脂质的胶束样品所采集的NOESY光谱表明存在特定的脂质-肽相互作用。根据所获得的NOE数据，对于所有三种二肽的反式构象异构体以及H-Tyr-Tic-NH-(CH2)2-Ph的顺式构象异构体，Tyr和Tic形成一个芳香簇，该芳香簇优先插入到胶束的脂质内部。对于顺式异构体，C端取代基在脂质相中的分配表现出更多样化的行为。H-Tyr-Tic-NH-(CH2)3-Ph和H-Tyr-Tic-NH-(CH2)2-cHx的顺式构象异构体优先通过其C端取代基锚定在胶束上，而H-Tyr-Tic-NH-(CH2)2-Ph中的相应区域保持柔性并浸没在水相中。所研究的三种化合物的顺式构象异构体中观察到的肽-胶束相互作用模式不一致，这可以根据其二肽取代基疏水性的差异来解释。取代基的疏水性越强，其优先插入胶束脂质核心的倾向就越大。对这三种肽测量的酰胺质子温度系数揭示了顺式和反式异构体之间的差异。在所研究的两种溶剂体系中，每种化合物反式构象异构体中的酰胺质子都高度暴露于水相，而每种肽的顺式NH质子仅部分暴露。这些结果表明，活性肽类似物的细微结构修饰可导致其生物活性及其在膜表面的分配模式发生显著变化。
