Structure activity relationship studies of MCH-related peptide ligands at SLC-1, the human melanin-concentrating hormone receptor.

Melanin-concentrating hormone(MCH) is a cyclic nonadecapeptide, involved in the regulation of feeding behavior, which acts through a G-protein coupled receptor (SLC-1) inhibiting adenylcyclase activity. In this study, fifty-seven analogues of MCH were investigated on the recently human clonedMCH receptor stably expressed in HEK293 cells, on both the inhibition of forskolin-stimulated cAMP production and [35S]-GTPγS binding. The dodecapeptide MCH6-17 [MCH ring between Cys 7 and Cys, with a single extra amino acid at the N-terminus (Arg) and at the C-terminus (Trp)] was found to be the minimal sequence required for a full and potent agonistic response on cAMP formation and [35S]-GTPγS binding. We Ala-scanned this dodecapeptide and found that only 3 out of 8 amino acids of the ring, namely Met, Arg and Tyr, were essential to elicit full and potent responses in both tests. Deletions inside the ring led either to inactivity or to poor antagonists with potencies in the μM range. Cys and Cys were substituted by Asp and Lys or one of their analogues, in an attempt to replace the disulfide bridge by an amide bond. However, those modifications were deleterious for agonistic activity. In [35S]-GTPγS binding, these compounds behaved as weak antagonists (KB 1-4 μM). Finally, substitution in MCH6-17 of 6 out of 12 amino acids by non natural residues and concomitant replacement of the disulfide bond by an amide bond led to three compounds with potent antagonistic properties (KB = 0.1-0.2 μM). Exploitation of these structure-activity relationships should open the way to the design of short and stable MCH peptide antagonists. by gest, on Jauary 8, 2013 w w w .jb.org D ow nladed fom