Structural determinants for binding to CGRP receptors expressed by human SK-N-MC and Col 29 cells: studies with chimeric and other peptides

1 Structure-activity relationships for the binding of human alpha-calcitonin gene-related peptide 8-37 (h alpha CGRP(8-37)) have been investigated at the CORP receptors expressed by human SK-N-MC (neuroblastoma) and Col 29 (colonic epithelia) cells by radioligand binding assays and functional assays (h alpha CGRP stimulation of adenylate cyclase). 2 On SK-N-MC cells the potency order was h alpha CGRP(8-37) > h alpha CGRP(19-37) = AC187 > rat amylins(8-37) > h alpha[Tyr(0)]-CGRP(28-37) (apparent pKBS of 7.49+/-0.25, 5.89+/-0.20, 6.18+/-0.19, 5.85+/-0.19 and 5.25+/-0.07). The SK-N-MC receptor appeared CGRP(1)-like. 3 On Col 29 cells, only h alpha CGRP(8-37) of the above compounds was able to antagonize the actions of h alpha CGRP (apparent pKB = 6.48+/-0.28). Its receptor appeared CGRP(2)-like. 4 h alpha[Ala(11,18)]-CGRP(8-37), where the amphipathic nature of the N-terminal alpha-helix has been reduced, bound to SK-N-MC cells a 100 fold less strongly than h alpha CGRP(8-37). 5 On SK-N-MC cells, h alpha CGRP(8-18), (28-37) (M433) and mastoparan-h alpha CGRP(28-37) (M432) had apparent pKBS of 6.64+/-0.16 and 6.42+/-0.26, suggesting that residues 19-27 play a minor role in binding. The physico-chemical properties of residues 8-18 may be more important than any specific side-chain interactions. 6 M433 was almost as potent as h alpha CGRP(8-37) on Co129 cells (apparent pKB=6.17+/-0.20). Other antagonists were inactive.