Studies on molecular structures and oligosaccharide-binding specificities of algal lectins

研究结果表明，12种藻凝集素对某些特定结构的N-聚糖如高甘露糖型、复合型或两者兼有型、forssman抗原或唾液酸刘易斯X均具有较强的结合特异性。高甘露糖型或复合型N-聚糖特异性凝集素可根据所识别的分支结构的不同进一步分为几类。因此，凝集素识别N-聚糖的分支部分。然而，有趣的是，N-聚糖的还原末端N-乙酰壳二糖对于这些凝集素与聚糖的结合是必不可少的，因为它们本身不与任何支链寡糖结合。在高甘露糖型N-聚糖特异性凝集素中，红色麒麟菜和蓝绿色颤藻凝集素的完整一级结构均为类甘露糖型，而红色麒麟菜和蓝绿色颤藻凝集素的完整一级结构均为类甘露糖型。 ...更多信息 HII是确定的。两种凝集素具有非常相似的序列，包括N-末端67个氨基酸的同源序列的串联重复结构。锯齿埃立克体凝集素（267个氨基酸，4个重复序列）和阿加德奥氏体凝集素（132个氨基酸，2个重复序列）的重复序列数目不同。另一方面，两种凝集素的重复序列的数目与每单体分子的寡糖结合位点的数目一致。结果表明，一个重复单元对应于一个寡糖识别结构域和单体凝集素凝集细胞具有多个碳水化合物结合位点上的每一个单一的多肽链。在同源性搜索中，令人惊讶的是，两种藻凝集素的序列显示出与细菌粘球菌凝集素的非常高的相似性，包括N-末端67个氨基酸的四个串联重复。因此，它发现了一个新的凝集素家族具有结构相似性之间存在的较低的生物体的红球藻，蓝绿球藻（蓝藻）和细菌。这是第一个在原核生物和真核生物之间发现凝集素分子结构相似性的例子。少

The research results showed that the lectins from twelve algal species examined have the highly binding specificity to some definite structures of oligosaccharides such as high-mannose type, complex type, or both type of N-glycans, forssman antigen, or sialyl Lewis X, respectively. The high-mannose or complex type N-glycan specific lectins were further divided into several groups by the difference of the branched structures recognized. The lectins thus recognize the branched moiety of the N-glycans. Interestingly, however, the reducing terminal N-acetylchitobiose of the N-glycans was essential for the binding of these lectins to the glycans, because they did not bind to any of the branched oligosaccharides themselves. Thus these algal lectins had the rigid binding specificity for some oligosaccharide structures.Among the high-mannose type N-glycan specific lectins, the complete primary structures of the lectins from the red alga Eucheuma serra and the blue-green alga Oscillatoria agard … More hii were determined. Both lectins had the very similar sequences to each other including the tandem repeat structures of homologous sequences of the N-terminal 67 amino acids. The number of the repeats was different between E.serra lectin (267 amino acids of 4 repeats) and O.agardhii lectin (132 amino acids of 2 repeats). On the other hand, the number of the repeats was well agreement with that of oligosaccharide-binding sites per a monomeric molecule for both lectins. The results indicate that a repeating unit corresponds to an oligosaccharide-recognition domain and the monomeric lectins agglutinate cells by having the multiple carbohydrate-binding sites on each single polypeptide chain. In homology search, surprisingly, the sequences of both algal lectins showed the very high similarity with that of a bacterium Myxococcus xanthus agglutinin including the four tandem repeats of the N-terminal 67 amino acids. Thus it found that a new lectin family having structural similarity was present among the lower organisms of the red alga, the blue-green alga (cyanobacterium) and the bacterium. This is the first example that the structural similarity of lectin molecules was found between prokaryote and eukaryote organisms. Less