Wada J, Kanwar Y S
Department of Pathology, Northwestern University Medical School, Chicago, Illinois 60611, USA.
J Biol Chem. 1997 Feb 28;272(9):6078-86. doi: 10.1074/jbc.272.9.6078.
A 36-kDa beta-galactoside mammalian lectin protein, designated as galectin-9, was isolated from mouse embryonic kidney by using a degenerate primer polymerase chain reaction and cloning strategy. Its deduced amino acid sequence had the characteristic conserved sequence motif of galectins. Endogenous galectin-9, extracted from liver and thymus, as well as recombinant galectin-9 exhibited specific binding activity for the lactosyl group. It had two distinct N- and C-terminal carbohydrate-binding domains connected by a link peptide, with no homology to any other protein. Galectin-9 had an alternate splicing isoform, exclusively expressed in the small intestine with a 31-amino acid insertion between the N-terminal domain and link peptide. Sequence homology analysis revealed that the C-terminal carbohydrate-binding domain of mouse galectin-9 had extensive similarity to that of monomeric rat galectin-5. The presence of galectin-5 in the mouse could not be demonstrated by polymerase chain reaction or by Northern or Southern blot genomic DNA analyses. Sequence comparison of rat galectin-5 and rat galectin-9 cDNA did not reveal identical nucleotide sequences in the overlapping C-terminal carbohydrate-binding domain, indicating that galectin-9 is not an alternative splicing isoform of galectin-5. However, galectin-9 had a sequence identical with that of its intestinal isoform in the overlapping regions in both species. Southern blot genomic DNA analyses, using the galectin-9 specific probe derived from the N-terminal carbohydrate-binding domain, indicated the presence of a novel gene encoding galectin-9 in both mice and rats. In contrast to galectin-5, which is mainly expressed in erythrocytes, galectin-9 was found to be widely distributed, i.e. in liver, small intestine, thymus > kidney, spleen, lung, cardiac and skeletal muscle > reticulocyte, brain. Collectively, these data indicate that galectin-9 is a new member of the galectin gene family and has a unique intestinal isoform.
一种分子量为36 kDa的β-半乳糖苷哺乳动物凝集素蛋白，命名为半乳糖凝集素-9，通过简并引物聚合酶链反应和克隆策略从小鼠胚胎肾中分离得到。其推导的氨基酸序列具有半乳糖凝集素特有的保守序列基序。从肝脏和胸腺中提取的内源性半乳糖凝集素-9以及重组半乳糖凝集素-9对乳糖基具有特异性结合活性。它有两个由连接肽连接的不同的N端和C端碳水化合物结合结构域，与其他任何蛋白质均无同源性。半乳糖凝集素-9有一个可变剪接异构体，仅在小肠中表达，在N端结构域和连接肽之间有一个31个氨基酸的插入序列。序列同源性分析表明，小鼠半乳糖凝集素-9的C端碳水化合物结合结构域与单体大鼠半乳糖凝集素-5的该结构域有广泛的相似性。通过聚合酶链反应、Northern或Southern印迹基因组DNA分析均未证实小鼠中存在半乳糖凝集素-5。大鼠半乳糖凝集素-5和大鼠半乳糖凝集素-9 cDNA的序列比较未发现重叠的C端碳水化合物结合结构域中有相同的核苷酸序列，这表明半乳糖凝集素-9不是半乳糖凝集素-5的可变剪接异构体。然而，在两个物种的重叠区域中，半乳糖凝集素-9与其肠道异构体的序列相同。使用源自N端碳水化合物结合结构域的半乳糖凝集素-9特异性探针进行的Southern印迹基因组DNA分析表明，小鼠和大鼠中均存在一个编码半乳糖凝集素-9的新基因。与主要在红细胞中表达的半乳糖凝集素-5不同，半乳糖凝集素-9分布广泛，即在肝脏、小肠、胸腺>肾脏、脾脏、肺、心肌和骨骼肌>网织红细胞、脑。总体而言，这些数据表明半乳糖凝集素-9是半乳糖凝集素基因家族的一个新成员，并且有一个独特的肠道异构体。
