Structure-activity studies of vasoactive intestinal polypeptide.

This report explores the potential side-chain functional groups required for interaction of the bronchodilator neuropeptide, vasoactive intestinal peptide (VIP), with its receptor. The binding affinity and biological activity of native VIP have been found to be sensitive to the removal of amino- and carboxyl-terminal residues. This data suggests that elements within the entire primary sequence of the VIP molecule appear to be necessary for recognition by VIP receptors. The introduction of alanine residues substituted into the VIP molecule is utilized to probe for side-chain functional groups that are crucial for eliciting high receptor binding affinity in vitro and high biological potency in vivo. The VIP pharmacophore appears to be identical in guinea pig lung and human lung and consists of multiple binding sites most likely involving positions Asp3, Phe6, Thr7, Tyr10, Tyr22, and Leu23. These findings could be exploited to enhance the biological potency of VIP by increasing the binding energy at these positions.