Zupanc G K, Siehler S, Jones E M, Seuwen K, Furuta H, Hoyer D, Yano H
Department of Biochemistry, The University of Chicago, Chicago, Illinois, 60637, USA.
Gen Comp Endocrinol. 1999 Sep;115(3):333-45. doi: 10.1006/gcen.1999.7316.
The actions of the various forms of somatostatin (SRIF), including those of the tetradecapeptide SRIF(14), are mediated by specific receptors. In mammals, five subtypes of SRIF receptors, termed sst(1-5), have been cloned. Using a combination of reverse transcriptase-polymerase chain reaction and genomic library screening in the gymnotiform fish Apteronotus albifrons, a gene encoding the first-known nonmammalian SRIF receptor has been isolated. The deduced amino acid sequence displays 59% identity with the human sst(3) receptor protein; hence, the gene is termed "Apteronotus sst(3)." The predicted protein consists of 494 amino acid residues exhibiting a putative seven-transmembrane domain topology typical of G protein-coupled receptors. A signal corresponding to the Apteronotus sst(3) receptor was detected in brain after amplification of poly(A)(+)-RNA by reverse transcriptase-polymerase chain reaction, but not by Northern blot analysis or in situ hybridization, suggesting a low level of expression. Membranes prepared from CCL39 cells stably expressing the Apteronotus sst(3) receptor gene bound [(125)I][Leu(8),d-Trp(22), (125) I-Tyr(25)]SRIF(28) with high affinity and in a saturable manner (B(max) = 4470 fmol/mg protein; pK(D) = 10.5). SRIF(14) and various synthetic SRIF receptor agonists produced a dose-dependent inhibition of radioligand binding, with the following rank order of potency: SRIF(14) approximately SRIF(28) > BIM 23052 > octreotide > BIM 23056. Under low stringency conditions, an Apteronotus sst(3) probe hybridized to multiple DNA fragments in HindIII or EcoRI digests of A. albifrons DNA, indicating that the Apteronotus sst(3) receptor is a member of a larger family of Apteronotus SRIF receptors.
各种形式的生长抑素（SRIF），包括十四肽SRIF(14) 的作用，是由特定受体介导的。在哺乳动物中，已克隆出五种SRIF受体亚型，称为sst(1 - 5)。通过在裸背电鳗Apteronotus albifrons中结合使用逆转录聚合酶链反应和基因组文库筛选，已分离出编码首个已知非哺乳动物SRIF受体的基因。推导的氨基酸序列与人类sst(3) 受体蛋白具有59% 的同一性；因此，该基因被称为“Apteronotus sst(3)”。预测的蛋白质由494个氨基酸残基组成，呈现出G蛋白偶联受体典型的假定七跨膜结构域拓扑结构。通过逆转录聚合酶链反应扩增poly(A)(+) - RNA后，在脑中检测到与Apteronotus sst(3) 受体相对应的信号，但通过Northern印迹分析或原位杂交未检测到，表明表达水平较低。从稳定表达Apteronotus sst(3) 受体基因的CCL39细胞制备的膜以高亲和力和可饱和方式结合[(125)I][Leu(8),d-Trp(22),(125)I-Tyr(25)]SRIF(28)（B(max)=4470 fmol/mg蛋白质；pK(D)=10.5）。SRIF(14) 和各种合成的SRIF受体激动剂产生了放射性配体结合的剂量依赖性抑制，其效力顺序如下：SRIF(14) 约等于SRIF(28) > BIM 23052 > 奥曲肽 > BIM 23056。在低严格条件下，Apteronotus sst(3) 探针与Apteronotus albifrons DNA的HindIII或EcoRI消化物中的多个DNA片段杂交，表明Apteronotus sst(3) 受体是Apteronotus SRIF受体大家族的一员。
