Structure, Function and Role of Vertebrate -Galactoside-binding Lectin

由于半乳糖苷结合凝集素在大多数脊椎动物中都有发现，并且在胚胎和肿瘤组织中都有显著的表达，因此它被认为参与了迄今为止尚未阐明的基本生物控制机制。我们从多个角度对其进行了研究，以阐明其生理功能，为其在医学上的应用开辟道路。首先，我们利用蛋白质测序仪完成了人胎盘凝集素的氨基酸序列测定。我们还成功地分离了它的cDNA克隆，并测定了它的核苷酸序列。同时还克隆了鸡16K凝集素的全长基因，并对其蛋白质编码区进行了序列分析。比较了以前确定的鸡14K的一级结构，发现它们彼此高度同源(例如人Placente/鸡14K，50%相同)，因此很明显它们来自共同的祖先蛋白。尽管它们位于细胞外，但它们的N端不包含任何可切割的信号序列也是它们之间的共同特征。将上述人凝集素基因插入到表达载体中，获得产生人凝集素的大肠杆菌细胞。他们有望提供足够数量的凝集素来研究其在医学上的应用。用电子显微镜和抗鸡14K凝集素抗体进行组织化学观察，发现其分布于表皮细胞桥粒及其周围，提示其参与了细胞间的相互作用。此外，对肿瘤组织的研究表明，这种凝集素也以自由分子的形式存在，这与正常组织中的凝集素有很大不同，正常组织中的凝集素大多与其他分子结合。这是非常有趣的，因为它表明凝集素的状态随着变化而变化。

Since -galactoside-binding lectin is found in most vertebrates and seen to be expressed in embryonic as well as tumor tissues remarkably, it is thought to participate in fundamental biological control mechanisms not elucidated so far. We have studied it from various points of view to clarify its physiological function as well as to open the way to apply it to medical use. Firstly, we completely determined the amino acid sequence of human placenta lectin using a protein sequencer. We also succeeded in the isolation of a cDNA clone for it and determined its nucleotide sequence. A cDNA for chick 16K lectin was also cloned and most of the protein-coding region was sequenced. The primary structures including that of chick 14K type determined before were compared and shown to be highly homologous one ANO ther (e.g. human placente/chick 14K, 50% identical), and thus it is obvious that they were originated from a common ancestor protein.The property that they do not contain any cleavable signal sequence at their N-terminus in spite of their extracellular localization is also common among them. The above human lectin cDNA was inserted into an expression vector to obtain E. coli cells that produce human lectin. They are expected to supply large amount of lectin enough to study the medical application of it. Histochemical observation using electron microscopy and anti-chick 14K lectin antibody has shown that it is distributed in and around the desmosome of epidermal cells suggesting its participation to the cell-to-cell interaction. Furthermore, studies on tumor tissues have shown that this kind of lectin also exists as a free molecule, which quite differs from that in normal tissue where most of it binds to other molecules. It is very interesting since it is suggested that the state of the lectin changes in accordance with transformation.