Holthuis J C, Martens G J
Department of Animal Physiology, University of Nijmegen, The Netherlands.
J Neurochem. 1996 Jun;66(6):2248-56. doi: 10.1046/j.1471-4159.1996.66062248.x.
Chromogranins and secretogranins are acidic secretory proteins of unknown function that represent major constituents of neuroendocrine secretary granules. Using a differential screening strategy designed to identify genes involved in peptide hormone biosynthesis and secretion, we have isolated cDNA clones encoding the first nonmammalian homologues of secretogranin II (SgII) and secretogranin III (SgIII) from a Xenopus intermediate pituitary cDNA library. A comparative analysis of the Xenopus and mammalian proteins revealed a striking regional conservation with an overall sequence identity of 48% for SgII and 61% for SgIII. One of the highly conserved and thus potentially functional domains in SgII corresponds to the bioactive peptide secretoneurin. However, in SgII and especially in SgIII, a substantial portion of the potential dibasic cleavage sites is not conserved, arguing against the idea that these granins serve solely as peptide precursors. Moreover, SgIII contains a conserved and repeated motif (DSTK) that is reminiscent of a repeat present in the trans-Golgi network integral membrane proteins TGN38 and TGN41, a finding more consistent with an intracellular function for this protein. When Xenopus intermediate pituitary cells were stimulated in vivo, the mRNA levels of SgII and SgIII increased dramatically (15- and 35-fold, respectively) and in parallel with that of the prohormone proopiomelanocortin (30-fold increase). Our results indicate that the process of peptide hormone production and release in a neuroendocrine cell involves multiple members of the granin family.
嗜铬粒蛋白和分泌粒蛋白是功能未知的酸性分泌蛋白，是神经内分泌分泌颗粒的主要成分。利用一种旨在鉴定参与肽激素生物合成和分泌的基因的差异筛选策略，我们从非洲爪蟾中间垂体cDNA文库中分离出了编码分泌粒蛋白II（SgII）和分泌粒蛋白III（SgIII）首个非哺乳动物同源物的cDNA克隆。对非洲爪蟾和哺乳动物蛋白的比较分析显示出显著的区域保守性，SgII的总体序列同一性为48%，SgIII为61%。SgII中一个高度保守因而可能具有功能的结构域对应于生物活性肽分泌神经肽。然而，在SgII尤其是SgIII中，相当一部分潜在的双碱性裂解位点并不保守，这与这些颗粒蛋白仅作为肽前体的观点相悖。此外，SgIII含有一个保守且重复的基序（DSTK），这让人联想到反式高尔基体网络整合膜蛋白TGN38和TGN41中存在的一个重复序列，这一发现与该蛋白的细胞内功能更为一致。当在体内刺激非洲爪蟾中间垂体细胞时，SgII和SgIII的mRNA水平显著增加（分别增加15倍和35倍），且与激素原阿黑皮素原的mRNA水平增加（增加30倍）同步。我们的结果表明，神经内分泌细胞中肽激素的产生和释放过程涉及颗粒蛋白家族的多个成员。
