Ma. Bednarek et al., Structure-function studies on the cyclic peptide MT-II, lactam derivative of alpha-melanotropin, PEPTIDES, 20(3), 1999, pp. 401-409
The alanine-substituted and the retro, enantio, and retro-enantio analogs o
f MT-II, a potent agonist at melanocortin (MC) receptors, were prepared by
solid-phase synthesis and evaluated for their ability to bind and activate
human MC3, MC4, and MC5 receptors. Replacement of His with Ala resulted in
[Ala(6)]-MT-II with affinity and agonist potency at human MC3, MC4, and MC5
receptors similar to MT-II. Substitution of Arg with Ala gave compound 100
-fold less potent than MT-II, but replacement of Phe or Trp with Ala led to
inactive compounds (at the micromolar concentrations). The significant dro
p of potency of the retro, enantio, and retro-enantio analogs of MT-II, dem
onstrated a crucial role of side-chain topology, and to a lesser degree, of
peptide backbone in interactions of MT-II with the melanocortin receptors.
The nuclear magnetic resonance analysis of MT-II suggested involvement of
Phe and Arg residues in H-bonds stabilizing the bent conformations of the p
eptide backbone. (C) 1999 Elsevier Science Inc. All rights reserved.