Nehring R B, Richter D, Meyerhof W
Institut für Zellbiochemie und klinische Neurobiologie, UKE, Hamburg, Germany.
J Physiol Paris. 2000 May-Aug;94(3-4):185-92. doi: 10.1016/s0928-4257(00)00203-5.
The somatostatin receptor subtypes, sst1-sst5, bind their natural ligands, somatostatin-14, somatostatin-28 and cortistatin-17, with high affinity but do not much discriminate between them. Detailed understanding of the interactions between these receptors and their peptide ligands may facilitate the development of selective compounds which are needed to identify the biological functions of individual receptor subtypes. The influence of the amino-terminal domain and of the two putative N-linked glycosylation sites located in this region of rat sst3 was analysed. Biochemical studies in transfected cell lines suggested that the amino-terminus of sst3 is glycosylated at both sites. Mutation of the N-linked glycosylation site, Asn18Thr, had only a small effect on binding properties and inhibition of adenylyl cyclase. The double mutant Asn18Thr/Asn31Thr lacking both glycosylation sites showed a significant reduction in high affinity binding and inhibition of adenylyl cyclase while peptide selectivity was not affected. Truncation of the amino-terminal region by 32 amino acid residues including the two glycosylation sites caused similar but much stronger effects. Immunocytochemical analysis of receptor localisation revealed that the amino-terminal domain but not the carbohydrates appear to be involved in the transport of the receptor polypeptide to the cell surface.
生长抑素受体亚型sst1 - sst5以高亲和力结合其天然配体——生长抑素 - 14、生长抑素 - 28和可体松素 - 17，但对它们的区分能力不强。深入了解这些受体与其肽类配体之间的相互作用，可能有助于开发出选择性化合物，而这些化合物是确定各个受体亚型生物学功能所必需的。分析了大鼠sst3这一区域的氨基末端结构域以及两个假定的N - 连接糖基化位点的影响。在转染细胞系中进行的生化研究表明，sst3的氨基末端在这两个位点均被糖基化。N - 连接糖基化位点Asn18突变为Thr，对结合特性和腺苷酸环化酶的抑制作用仅有微小影响。缺乏两个糖基化位点的双突变体Asn18Thr/Asn31Thr在高亲和力结合和腺苷酸环化酶抑制方面显著降低，而肽选择性不受影响。包括两个糖基化位点在内的32个氨基酸残基对氨基末端区域的截短产生了类似但更强的影响。受体定位的免疫细胞化学分析表明，氨基末端结构域而非碳水化合物似乎参与了受体多肽向细胞表面的转运。
