Martens G J, Civelli O, Herbert E
J Biol Chem. 1985 Nov 5;260(25):13685-9.
The function of alpha-melanocyte-stimulating hormone (alpha-MSH) is not known in mammals. It is well-established in the amphibian Xenopus laevis in which alpha-MSH mediates the process of adaptation to a dark background. The amino acid sequence of this hormone is, however, not known in amphibians. In order to determine the primary structure of the precursor protein for alpha-MSH, which in mammals has been called pro-opiomelancortin (POMC), we constructed a cDNA library from Xenopus pituitary mRNA. A pool of synthetic oligodeoxyribonucleotide tetradecamers corresponding to part of the mammalian alpha-MSH sequence was used to screen the library. The nucleotide sequence of a 1050-base pair hybridization-positive cDNA clone was determined and the deduced amino acid sequence of Xenopus POMC revealed the sequences of Xenopus gamma-MSH, alpha-MSH, corticotropin-like intermediate lobe peptide, beta-MSH, and beta-endorphin. Interestingly, the N-terminal amino acid of Xenopus alpha-MSH, which is N alpha-acetylated in the biologically active form of the hormone, is different from that of mammalian alpha-MSH. The distribution of the bioactive domains within Xenopus POMC is remarkably similar to that in other known POMC molecules and as in mammals the domains in the amphibian prohormone are flanked on both sides by pairs of basic amino acids.
α-黑素细胞刺激素（α-MSH）在哺乳动物中的功能尚不清楚。在两栖动物非洲爪蟾中，α-MSH介导对深色背景的适应过程，这一点已得到充分证实。然而，这种激素在两栖动物中的氨基酸序列尚不清楚。为了确定α-MSH前体蛋白的一级结构，在哺乳动物中该前体蛋白被称为阿黑皮素原（POMC），我们从非洲爪蟾垂体mRNA构建了一个cDNA文库。使用一组与哺乳动物α-MSH序列部分相对应的合成寡脱氧核糖核苷酸十四聚体来筛选该文库。测定了一个1050碱基对的杂交阳性cDNA克隆的核苷酸序列，非洲爪蟾POMC推导的氨基酸序列揭示了非洲爪蟾γ-MSH、α-MSH、促肾上腺皮质激素样中叶肽、β-MSH和β-内啡肽的序列。有趣的是，非洲爪蟾α-MSH的N端氨基酸在激素的生物活性形式中是Nα-乙酰化的，与哺乳动物α-MSH的N端氨基酸不同。非洲爪蟾POMC中生物活性结构域的分布与其他已知的POMC分子非常相似，并且与哺乳动物一样，两栖动物前体激素中的结构域两侧都有一对碱性氨基酸。
