Stereochemical requirements for receptor recognition of the mu-opioid peptide endomorphin-1.
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.
Paterlini
M G
MG
Department of Medicinal Chemistry and Supercomputer Institute, Biophysics, and Molecular Biology, University of Minnesota, Minneapolis, Minnesota 55455, USA. germana1@vw1.medc.umn.edu
Avitabile
F
F
Ostrowski
B G
BG
Ferguson
D M
DM
Portoghese
P S
PS
D000818:Animals; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000737:chemistry; D006168:Guinea Pigs; D007082:Ileum / Q000187:drug effects; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009842:Oligopeptides / Q000737:chemistry* / Q000494:pharmacology; D011487:Protein Conformation; D017450:Receptors, Opioid, mu / Q000737:chemistry*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
D009842:Oligopeptides; D017450:Receptors, Opioid, mu; C105293:endomorphin 1; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-