Holbrook Joanna D, Danpure Christopher J
Department of Biology, University College London, Gower Street, London WC1E 6BT, United Kingdom.
J Biol Chem. 2002 Jan 18;277(3):2336-44. doi: 10.1074/jbc.M107047200. Epub 2001 Nov 2.
To gain further insights into the molecular basis of the evolution of alanine:glyoxylate aminotransferase (AGT) intracellular targeting in vertebrates, we have studied the molecular basis of its dual mitochondrial and cytosolic distribution in amphibian liver cells. The AGT gene in Xenopus laevis encodes a polypeptide of 415 amino acids, which includes a 24-residue N-terminal mitochondrial targeting sequence (MTS), at either end of which are located two in-frame potential translation start sites. This MTS is necessary to target Xenopus AGT and sufficient to target a green fluorescent fusion protein to mitochondria in transfected COS cells. The C-terminal tripeptide (KKM), despite being similar to the nonconsensus type 1 peroxisomal targeting sequence in human AGT (KKL), was unable to target Xenopus AGT or human AGT to peroxisomes. The Xenopus AGT gene produces two types of transcript. The longer form encodes a polypeptide that contains the MTS and is targeted to mitochondria. The shorter form encodes a polypeptide that does not contain the MTS and remains in the cytosol. These results are discussed not only in terms of the molecular evolution of AGT targeting but also in terms of the ancillary requirements for the peroxisomal targeting of human AGT.
乙醛酸转氨酶（AGT）细胞内靶向进化的分子基础，我们研究了其在两栖类肝细胞中双重线粒体和胞质分布的分子基础。非洲爪蟾的AGT基因编码一个由415个氨基酸组成的多肽，其中包括一个24个残基的N端线粒体靶向序列（MTS），在其两端各有两个符合读框的潜在翻译起始位点。这个MTS对于非洲爪蟾AGT的靶向定位是必需的，并且足以将绿色荧光融合蛋白靶向到转染的COS细胞中的线粒体。C端三肽（KKM），尽管与人AGT中的非一致性1型过氧化物酶体靶向序列（KKL）相似，但无法将非洲爪蟾AGT或人AGT靶向到过氧化物酶体。非洲爪蟾AGT基因产生两种类型的转录本。较长的形式编码一个包含MTS并靶向线粒体的多肽。较短的形式编码一个不包含MTS并留在胞质溶胶中的多肽。这些结果不仅从AGT靶向的分子进化角度进行了讨论，还从人AGT过氧化物酶体靶向的辅助要求角度进行了讨论。
