Conformations of End-Capped Melanocortin Agonists RCO-X-Z-Arg-Trp-NH2 by 2D-NMR, CD and Computations

摘要

Natural agonists of melanocortin receptors (MCR) α-, β- and y-melanocyte stimulating hormones (MSH) share the common melanocortin core sequence His~6-Phe~7-Arg -Trp~9 (HFRW) existing in a P-turn conformation [1]. Stabilization of the (3-turn conformation in MSH synthetic analogs (NDP-MSH, MT-II) with the His~6-D-Phe~7-Arg~8-Trp~9 (HfRW) core is believed to be responsible for their increased potency [1,2]. Despite high potency, these peptide agonists are non-selective at MCI, MC3, MC4 and MC5Rs. Recently, we have reported [3] a superpotent hMClR selective agonist LK-184 Ph(CH2)3CO-HfRW-NH2 (1) with an EC_950) of 0.01 nM and ca. 500-fold selectivity for hMClR compared to hMC3 and hMC4Rs and LK-394 Ph(CH2)3COHfR-NH2 (2) - a full hMCl agonist with an EC_(50) of 5 nM and weak partial agonism at hMC3/4Rs. In order to understand the origin of melanocortin activity of short linear peptides, conformations of 1, 2, the core tetrapeptide Ac-HfRW-NH2 (3), and analogs of 1 with (3-turn stabilizing AAs (4-8) were studied by 2D-NMR in CD3OH, circular dichroism (CD), NMR constrained MD (Insight II, CVFF force field) and conformational analysis (Macromodel, OPLS_2005 in water, MCMM).