Functional characterization of structural alterations in the sequence of the vasodilatory peptide maxadilan yields a pituitary adenylate cyclase-activating peptide type 1 receptor-specific antagonist

Maxadilan is a vasodilatory peptide derived from sand flies that is an agon ist at the pituitary adenylate cyclase-activating peptide (PACAP) type 1 re ceptor. Surprisingly, maxadilan does not share significant sequence homolog y with PACAP, To examine the relationship between structure and activity of maxadilan, several amino acid substitutions and deletions were made in the peptide. These peptides were examined in vitro for binding to crude membra nes derived from rabbit brain, a tissue that expresses PACAP type 1 recepto rs; and induction of cAMP was determined in PC12 cells, a line that express es these receptors, The peptides were examined in vivo for their ability to induce erythema in rabbit skin. Substitution of the individual cysteines a t positions 1 and 5 or deletion of this ring structure had little effect on activity. Substitution of either cysteine at position 14 or 51 eliminated activity. Deletion of the 19 amino acids between positions 24 and 42 result ed in a peptide with binding, but no functional activity. The capacity of t his deletion mutant to interact with COS cells transfected with the PACAP t ype 1 receptor revealed that this peptide was a specific antagonist to the PACAP type 1 receptor.