Gaidamashvili Mariam, Ohizumi Yuki, Iijima Shinichiro, Takayama Tomo, Ogawa Tomohisa, Muramoto Koji
Department of Biomolecular Science, Graduate School of Life Sciences, Tohoku University, Sendai 981-8555, Japan.
J Biol Chem. 2004 Jun 18;279(25):26028-35. doi: 10.1074/jbc.M402139200. Epub 2004 Mar 26.
Four major proteins designated DB1, DB2, DB3, and DB4 were isolated and characterized from the yam tuber Dioscorea batatas. The ratios of their yields were 20:50:20:10. DB1 was a mannose-binding lectin (20 kDa) consisting of 10-kDa subunits and was classified as the monocot mannose-binding lectin family. DB2, accounting for 50% of the total protein, was the storage protein, commonly called dioscorins consisting of a 31-kDa subunit. On the basis of amino acid sequence, DB2 was classified to be dioscorin A. DB3 was a maltose-binding lectin, having an apparent molecular mass of 120 kDa and composed of a 66-kDa subunit and two 31-kDa subunits (DB3S). The 66-kDa subunit was further composed of two 31-kDa subunits (DB3L) cross-linked by disulfide bonds. DB3L and DB3S (242 and 241 amino acid residues, respectively) were homologous with each other with 72% sequence identity. They showed a sequence homology to dioscorin B and dioscorin A from Dioscorea alata, with 90 and 93% identity, respectively, and to carbonic anhydrase from Arabidopsis thaliana with about 45% identity. DB3S had one intrachain disulfide bond located at Cys(28)-Cys(187), whereas DB3L had one interchain disulfide bond (Cys(40)-Cys(40)') in addition to the intrachain disulfide bond (Cys(28)-Cys(188)) to form a 66-kDa subunit. DB1 and DB3 agglutinated rabbit erythrocytes at 2.7 and 3.9 microg/ml, respectively. Despite the structural homology between DB2 and DB3, DB2 had no lectin activity. The 66-kDa subunit itself revealed the full hemagglutinating activity of DB3, indicating that DB3L but not DB3S was responsible for the activity. The hemagglutinating activity of DB3 required Ca(2+) ions and was exclusively inhibited by maltose and oligomaltoses (e.g. maltopentaose and maltohexaose) but not by d-glucose. DB3 could not be classified into any known plant lectin family. DB4 was a chitinase, homologous to an acidic chitinase from Dioscorea japonica. DB1, DB2, and DB3 did not show any activity of carbonic anhydrase, amylase, or trypsin inhibitor activity. These results show that two of the four major proteins isolated from the yam tubers D. batatas have unique lectin activities.
从薯蓣科植物甘薯的块茎中分离并鉴定出了四种主要蛋白质，分别命名为DB1、DB2、DB3和DB4。它们的产量比为20:50:20:10。DB1是一种甘露糖结合凝集素（20 kDa），由10 kDa的亚基组成，属于单子叶甘露糖结合凝集素家族。占总蛋白50%的DB2是储存蛋白，通常称为薯蓣球蛋白，由一个31 kDa的亚基组成。根据氨基酸序列，DB2被归类为薯蓣球蛋白A。DB3是一种麦芽糖结合凝集素，表观分子量为120 kDa，由一个66 kDa的亚基和两个31 kDa的亚基（DB3S）组成。66 kDa的亚基进一步由两个通过二硫键交联的31 kDa的亚基（DB3L）组成。DB3L和DB3S（分别有242和241个氨基酸残基）彼此同源，序列同一性为72%。它们与来自参薯的薯蓣球蛋白B和薯蓣球蛋白A的序列同源性分别为90%和93%，与拟南芥的碳酸酐酶的序列同源性约为45%。DB3S在Cys(28)-Cys(187)处有一个链内二硫键，而DB3L除了在Cys(28)-Cys(188)处有一个链内二硫键外，还有一个链间二硫键（Cys(40)-Cys(40)'）以形成一个66 kDa的亚基。DB1和DB3分别在2.7和3.9 μg/ml时凝集兔红细胞。尽管DB2和DB3在结构上有同源性，但DB2没有凝集素活性。6 kDa的亚基本身显示出DB3的全部血凝活性，表明负责该活性的是DB3L而不是DB3S。DB3的血凝活性需要Ca(2+)离子，并且仅被麦芽糖和低聚麦芽糖（如麦芽五糖和麦芽六糖）抑制，而不被d-葡萄糖抑制。DB3不能被归类到任何已知的植物凝集素家族中。DB4是一种几丁质酶，与来自日本薯蓣的酸性几丁质酶同源。DB1、DB2和DB3没有显示出任何碳酸酐酶、淀粉酶或胰蛋白酶抑制剂活性。这些结果表明，从甘薯块茎中分离出的四种主要蛋白质中的两种具有独特的凝集素活性。
