Vilardaga J P, di Paolo E, de Neef P, Waelbroeck M, Bollen A, Robberecht P
Department of Biochemistry and Nutrition, School of Medicine, Université Libre de Bruxelles, Belgium.
Biochem Biophys Res Commun. 1996 Jan 26;218(3):842-6. doi: 10.1006/bbrc.1996.0150.
The contribution of the extracellular loops of the secretin receptor to the recognition of secretin was investigated by transfection in CHO cells of chimeric receptors, in which the three loops of the secretin recombinant receptor were replaced by the corresponding sequences of the glucagon receptor. The role of the third loop could not be evaluated as the transfected cells did not respond to secretin. Replacement of extracellular loop 2 reduced markedly the capability of secretin to occupy the receptor but did not alter the capacity of the receptor to discriminate between peptide analogues modified in position 3. Replacement of the first extracellular loop not only reduced the potency of secretin but also decreased the capacity of the receptor to discriminate between ligands having in position 3 an aspartate (as in secretin), an asparagine, or a glutamic acid. This change in receptor properties was reproduced by a single mutation of lysine 173 of the receptor into isoleucine. Thus, the basic amino acid in position 173 is likely to interact with aspartate 3 of secretin. As an aspartate is also present in position 3 of VIP and PACAP, two peptides related to secretin, and a lysine residue is conserved in the first extracellular loop of the VIP and PACAP receptors, this interaction may be a key element of peptide recognition by this receptor family.
通过在CHO细胞中对嵌合受体进行转染，研究了促胰液素受体细胞外环对促胰液素识别的贡献。在这些嵌合受体中，促胰液素重组受体的三个环被胰高血糖素受体的相应序列所取代。由于转染细胞对促胰液素无反应，因此无法评估第三环的作用。细胞外环2的替换显著降低了促胰液素占据受体的能力，但并未改变受体区分在第3位修饰的肽类似物的能力。第一细胞外环的替换不仅降低了促胰液素的效力，还降低了受体区分在第3位具有天冬氨酸（如促胰液素中）、天冬酰胺或谷氨酸的配体的能力。受体性质的这种变化可通过将受体的赖氨酸173单突变为异亮氨酸来重现。因此，第173位的碱性氨基酸可能与促胰液素的天冬氨酸3相互作用。由于与促胰液素相关的两种肽——血管活性肠肽（VIP）和垂体腺苷酸环化酶激活肽（PACAP）在第3位也存在天冬氨酸，并且VIP和PACAP受体的第一细胞外环中保守有一个赖氨酸残基，这种相互作用可能是该受体家族识别肽的关键因素。
