Sakakura Masayoshi, Oo-Puthinan Sarawut, Moriyama Chifumi, Kimura Tomomi, Moriya Jun, Irimura Tatsuro, Shimada Ichio
Laboratories of Physical Chemistry, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Hongo 7-3-1, Tokyo 113-0033, Japan.
J Biol Chem. 2008 Nov 28;283(48):33665-73. doi: 10.1074/jbc.M804067200. Epub 2008 Sep 12.
Macrophage galactose-type C-type lectins 1 and 2 (MGL1/2) are expressed on the surfaces of macrophages and immature dendritic cells. Despite the high similarity between the primary sequences of MGL1 and MGL2, they display different ligand specificities. MGL1 shows high affinity for the LewisX trisaccharide, whereas MGL2 shows affinity for N-acetylgalactosamine. To elucidate the structural basis for the ligand specificities of the MGLs, we performed NMR analyses of the MGL1-LewisX complex. To identify the LewisX binding site on MGL1, a saturation transfer experiment for the MGL1-LewisX complex where sugar-CH/CH2-selective saturation was applied was carried out. To obtain sugar moiety-specific information on the interface between MGL1 and the LewisX trisaccharide, saturation transfer experiments where each of galactose-H5-, fucose-CH3-, and N-acetylglucosamine-CH3-selective saturations was applied to the MGL1-LewisX complex were performed. Based on these results, we present a LewisX binding mode on MGL1 where the galactose moiety is bound to the primary sugar binding site, including Asp-94, Trp-96, and Asp-118, and the fucose moiety interacts with the secondary sugar binding site, including Ala-89 and Thr-111. Ala-89 and Thr-111 in MGL1 are replaced with arginine and serine in MGL2, respectively. The hydrophobic environment formed by a small side chain of Ala-89 and a methyl group of Thr-111 is a requisite for the accommodation of the fucose moiety of the LewisX trisaccharide within the sugar binding site of MGL1.
巨噬细胞半乳糖型C型凝集素1和2（MGL1/2）表达于巨噬细胞和未成熟树突状细胞表面。尽管MGL1和MGL2的一级序列高度相似，但它们表现出不同的配体特异性。MGL1对LewisX三糖具有高亲和力，而MGL2对N-乙酰半乳糖胺具有亲和力。为了阐明MGLs配体特异性的结构基础，我们对MGL1-LewisX复合物进行了核磁共振分析。为了确定MGL1上的LewisX结合位点，对MGL1-LewisX复合物进行了糖-CH/CH2选择性饱和的饱和转移实验。为了获得关于MGL1与LewisX三糖之间界面的糖部分特异性信息，对MGL1-LewisX复合物进行了半乳糖-H5-、岩藻糖-CH3-和N-乙酰葡糖胺-CH3-选择性饱和的饱和转移实验。基于这些结果，我们提出了MGL1上的LewisX结合模式，其中半乳糖部分与主要糖结合位点结合，包括Asp-94、Trp-96和Asp-118，岩藻糖部分与次要糖结合位点相互作用，包括Ala-89和Thr-111。MGL1中的Ala-89和Thr-111在MGL2中分别被精氨酸和丝氨酸取代。由Ala-89的小侧链和Thr-111的甲基形成的疏水环境是LewisX三糖的岩藻糖部分在MGL1的糖结合位点内得以容纳的必要条件。
