X-RAY CRYSTAL-STRUCTURE OF THE SOYBEAN AGGLUTININ CROSS-LINKED WITH A BIANTENNARY ANALOG OF THE BLOOD-GROUP-I CARBOHYDRATE ANTIGEN
X-RAY CRYSTAL-STRUCTURE OF THE SOYBEAN AGGLUTININ CROSS-LINKED WITH A BIANTENNARY ANALOG OF THE BLOOD-GROUP-I CARBOHYDRATE ANTIGEN
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DOI：
10.1021/bi00015a004
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发表时间：
1995-04-18
期刊：
影响因子：
2.9
通讯作者：
SACCHETTINI, JC
中科院分区：
文献类型：
--
作者：
DESSEN, A;GUPTA, D;SACCHETTINI, JC
大豆凝集素 (SBA) (Glycine max) 是一种四聚体 GalNAc/Gal 特异性凝集素，最近据报道与一系列天然存在和合成的多触角碳水化合物（末端有 GalNAc 或 Gal 残基）形成独特的、高度组织化的交联复合物 [Gupta, D.、Bhattacharyya, L.、Fant, J.、Macaluso, F.、Sabesan, S. 和Brewer, C. F. (1994) 生物化学 33, 7495-7504]。为了阐明这些复合物的性质，报道了与 I 型血碳水化合物抗原的双触角类似物交联的 SBA 的 X 射线晶体结构。该结构表明，二价五糖 (β-LacNAc)(2)Gal-β-R 的桥联作用独特地促进了晶格形成，其中 R 是 -O(CH2)(5)COOCH3，β-LacNAc 部分连接到核心 Gal 的 2 和 6 位。因此，通过分子置换技术确定了与合成双触角五糖复合的 SBA 结构，并以 2.6 埃分辨率精修至 R 值为 20.1%。晶体呈六角形，具有 P6(4)22 空间群，与游离蛋白质的晶体显着不同。在结构中，每个单体不对称单元在 Asn 75 处包含一条 Man(9) 寡甘露糖型链，仅前两个 GlcNAc 残基可见。 SBA 亚基的整体三级结构与其他豆类凝集素以及某些动物凝集素相似。然而，SBA 四聚体中的二聚体界面是不寻常的，因为空间上仅允许一条完整的肽链，因此需要将一个 C 端片段化亚基与完整亚基并置。 SBA 四聚体之间的结合涉及五糖末端 Gal 残基在每个单体中相同位点的结合，其中糖与对称相关的相邻分子交联。交联五糖处于具有伪2重对称轴的构象，该伪2重对称轴位于晶格的晶体学2重对称轴上。因此，二价寡糖和凝集素的对称性是晶格的结构决定因素。从多维碳水化合物-凝集素交联复合物以及多价凝集素的信号转导特性方面讨论了结果。
Soybean agglutinin (SBA) (Glycine max), which is a tetrameric GalNAc/Gal-specific lectin, has recently been reported to form: unique, highly organized cross-linked complexes with a series of naturally occurring and synthetic multiantennary carbohydrates with terminal GalNAc or Gal residues [Gupta, D., Bhattacharyya, L., Fant, J., Macaluso, F., Sabesan, S., and Brewer, C. F. (1994) Biochemistry 33, 7495-7504]. In order to elucidate the nature of these complexes, the X-ray crystallographic structure of SBA cross-linked with a biantennary analog of the blood group I carbohydrate antigen is reported. The structure reveals that lattice formation is promoted uniquely by the bridging action of the bivalent pentasaccharide (beta-LacNAc)(2)Gal-beta-R, where R is -O(CH2)(5)COOCH3 and the beta-LacNAc moieties are linked to the 2 and 6 positions of the core Gal. The structure of SBA complexed with the synthetic biantennary pentasaccharide has thus been determined by molecular replacement techniques and refined at 2.6 Angstrom resolution to an R value of 20.1%. The crystals are hexagonal with a P6(4)22 space group, which differs significantly from that of crystals of the free protein. In the structure, each monomeric asymmetric unit contains a Man(9) oligomannose-type chain at Asn 75, with only the first two GlcNAc residues visible. The overall tertiary structure of the SBA subunit is similar to that of other legume lectins as well as certain animal lectins. However, the dimer interface in the SBA tetramer is unusual in that only one complete peptide chain is sterically permitted, thus requiring juxtapositioning of one C-terminal fragmented subunit together with an intact subunit. Association between SBA tetramers involves binding of the terminal Gal residues of the pentasaccharide at identical sites in each monomer, with the sugar cross-linking to a symmetry-related neighbor molecule. The cross-linking pentasaccharide is in a conformation that possesses a pseudo-2-fold axis of symmetry which lies on a crystallographic 2-fold axis of symmetry of the lattice. Hence, the symmetry properties of the bivalent oligosaccharide as well as the lectin are structural determinants of the lattice. The results are discussed in terms of multidimensional carbohydrate-lectin cross-linked complexes, as well as the signal transduction properties of multivalent lectins.