Gourlet P, Vandermeers A, Vandermeers-Piret M C, De Neef P, Waelbroeck M, Robberecht P
Department of Biochemistry and Nutrition, Faculty of Medicine, Université Libre de Bruxelles, Belgium.
Biochim Biophys Acta. 1996 Dec 12;1314(3):267-73. doi: 10.1016/s0167-4889(96)00106-1.
Rabbit secretin, which differs from all other mammalian secretins in having a Leu residue in position 6 (instead of Phe) and a basic residue (Arg) in position 16, had a lower affinity than porcine secretion on recombinant rat secretin receptors but had a greater affinity than porcine secretin on recombinant rat VIP1 and PACAP I receptors. Synthetic [L6] porcine secretin had a reduced potency on secretin and VIP1 receptors whereas [R16] porcine secretin had a similar binding profile as rabbit secretin. Thus, an arginine residue in position 16 reduced 3-fold the affinity of secretin for secretin receptors but increased 30-fold its affinity for the VIP1 and PACAP I receptors. The introduction of an arginine residue in position 16, instead of glutamine, in VIP and PACAP had a similar effect: [R16] VIP and [R16] PACAP had 3- to 10-fold higher affinities than VIP and PACAP for VIP1 and PACAP I receptors, and 3-fold lower affinities for the secretin receptors. The three [R16] peptides also had a reduced potency on the chimeric receptor consisting of the N-terminal part of the secretin receptor grafted on the VIP1 receptor, and an enhanced potency on the chimeric receptor consisting of the N-terminal part of VIP1 receptor grafted on the secretin receptor, indicating that position 16 of each ligand interacted with the N-terminal extracellular domain of the receptors.
兔促胰液素在第6位氨基酸残基为亮氨酸（而非苯丙氨酸），第16位为碱性氨基酸残基（精氨酸），这与所有其他哺乳动物促胰液素不同。在重组大鼠促胰液素受体上，兔促胰液素的亲和力低于猪促胰液素，但在重组大鼠VIP1和PACAP I受体上，其亲和力高于猪促胰液素。合成的[L6]猪促胰液素对促胰液素和VIP1受体的效力降低，而[R16]猪促胰液素的结合特征与兔促胰液素相似。因此，第16位的精氨酸残基使促胰液素对促胰液素受体的亲和力降低了3倍，但使其对VIP1和PACAP I受体的亲和力增加了30倍。在VIP和PACAP的第16位引入精氨酸残基（而非谷氨酰胺）有类似效果：[R16] VIP和[R16] PACAP对VIP1和PACAP I受体的亲和力比VIP和PACAP高3至10倍，对促胰液素受体的亲和力低3倍。这三种[R16]肽对由嫁接到VIP1受体上的促胰液素受体N端部分组成的嵌合受体的效力也降低，而对由嫁接到促胰液素受体上的VIP1受体N端部分组成的嵌合受体的效力增强，表明每个配体的第16位与受体的N端细胞外结构域相互作用。
