Paterlini M G, Avitabile F, Ostrowski B G, Ferguson D M, Portoghese P S
Department of Medicinal Chemistry and Supercomputer Institute, Biophysics, and Molecular Biology, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Biophys J. 2000 Feb;78(2):590-9. doi: 10.1016/S0006-3495(00)76619-7.
A series of diastereoisomers of endomorphin-1 (EM1, Tyr(1)-Pro(2)-Trp(3)-Phe(4)-NH(2)) have been synthesized and their potency measured using the guinea pig ileum assay. [D-Phe(4)]EM1 possessed 1/10 the potency of EM1, while potencies of [D-Tyr(1)]EM1 and [D-Trp(3)]EM1 were 50- and 100-fold lower, respectively. Drastic loss of activity occurred in the [D-Pro(2)]EM1 peptide. The structural determinants for the inactivity and reduced potency of the diastereoisomers were investigated using NMR spectroscopy and conformational analysis. Simulations of trans-[D-Pro(2)]EM1 using NOE-derived distance constraints afforded well-defined structures in which Tyr and Trp side chains stack against the proline ring. The inactivity of [D-Pro(2)]EM1 was explained by structural comparison with EM1 (, FEBS Lett. 439:13-20). The two peptides showed an opposite orientation of the Trp(3) residue with respect to Tyr(1), thus suggesting a role of Pro(2) as a stereochemical spacer in orienting Trp(3) and Phe(4) toward regions suitable for mu-receptor interaction. The agonist activity of [D-Tyr(1)]EM1 and [D-Trp(3)]EM1 was attributed to their ability to adopt low-energy conformations that mimic those of EM1. The requirements for mu-receptor activation were examined further by comparing EM1 with the mu-peptide [D-Ala(2), MePhe(4), Gly-ol]-enkephalin (DAMGO). Conformations of DAMGO with a Tyr(1)-MePhe(4) phenyl ring separation of approximately 12 A were found to mimic Tyr(1)-Phe(4) of EM1, thus suggesting overlapping binding modes between these two peptides.
已合成了一系列内吗啡肽-1（EM1，Tyr(1)-Pro(2)-Trp(3)-Phe(4)-NH₂）的非对映异构体，并使用豚鼠回肠试验测定了它们的效价。[D-Phe(4)]EM1的效价为EM1的1/10，而[D-Tyr(1)]EM1和[D-Trp(3)]EM1的效价分别低50倍和100倍。[D-Pro(2)]EM1肽的活性急剧丧失。使用核磁共振光谱和构象分析研究了非对映异构体无活性和效价降低的结构决定因素。使用源自NOE的距离约束对反式-[D-Pro(2)]EM1进行模拟，得到了明确的结构，其中Tyr和Trp侧链堆积在脯氨酸环上。通过与EM1进行结构比较解释了[D-Pro(2)]EM1的无活性（《欧洲生物化学学会联合会快报》439:13 - 20）。这两种肽显示出Trp(3)残基相对于Tyr(1)的相反取向，因此表明Pro(2)作为立体化学间隔物在将Trp(3)和Phe(4)定向到适合与μ受体相互作用的区域中发挥作用。[D-Tyr(1)]EM1和[D-Trp(3)]EM1的激动剂活性归因于它们能够采用模拟EM1的低能量构象。通过将EM1与μ肽[D-Ala(2), MePhe(4), Gly-ol]-脑啡肽（DAMGO）进行比较，进一步研究了μ受体激活的要求。发现DAMGO的Tyr(1)-MePhe(4)苯环间距约为12 Å的构象模拟了EM1的Tyr(1)-Phe(4)，因此表明这两种肽之间存在重叠的结合模式。
