Contributions of phenylalanine 335 to ligand recognition by human surfactant protein D - Ring interactions with SP-D ligands
Contributions of phenylalanine 335 to ligand recognition by human surfactant protein D - Ring interactions with SP-D ligands
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DOI：
10.1074/jbc.m601749200
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发表时间：
2006-06-30
影响因子：
4.8
通讯作者：
Head, James
中科院分区：
文献类型：
--
作者：
Crouch, Erika;McDonald, Barbara;Head, James
表面活性蛋白D（SP-D）是一种先天性免疫效应子，有助于抗微生物宿主防御和免疫调节。SP-D与微生物和有机抗原的相互作用涉及糖缀合物与C型凝集素碳水化合物识别结构域（CRD）的结合。编码人颈+ CRD的三聚体融合蛋白以比麦芽糖（原型竞争者）高近对数倍的亲和力结合至芳香糖苷对硝基苯基-α-D-麦芽糖苷。麦芽三糖，其具有与麦芽糖苷相同的键合模式，以中等亲和力结合。亮氨酸对苯丙氨酸335（Phe-335）的定点取代降低了对麦芽糖苷和麦芽三糖的亲和力，而不显著改变对麦芽糖或葡萄糖的亲和力，并且酪氨酸或色氨酸对亮氨酸的取代恢复了对麦芽三糖和麦芽糖苷的优先结合。在该位置具有丙氨酸的突变体不能结合甘露聚糖或麦芽糖取代的固体支持物。与麦芽三糖或对硝基苯基-麦芽糖苷复合的人颈+ CRD的晶体学分析显示末端葡萄糖或硝基苯基环与Phe-335的芳环的堆叠。我们的研究表明，Phe-335，这是进化上保守的所有已知的SP-D，发挥重要的，如果不是关键的，SP-D功能。
Surfactant protein D (SP-D) is an innate immune effector that contributes to antimicrobial host defense and immune regulation. Interactions of SP-D with microorganisms and organic antigens involve binding of glycoconjugates to the C-type lectin carbohydrate recognition domain (CRD). A trimeric fusion protein encoding the human neck + CRD bound to the aromatic glycoside p-nitrophenyl-alpha-D-maltoside with nearly a log-fold higher affinity than maltose, the prototypical competitor. Maltotriose, which has the same linkage pattern as the maltoside, bound with intermediate affinity. Site-directed substitution of leucine for phenylalanine 335 (Phe-335) decreased affinities for the maltoside and maltotriose without significantly altering the affinity for maltose or glucose, and substitution of tyrosine or tryptophan for leucine restored preferential binding to maltotriose and the maltoside. A mutant with alanine at this position failed to bind to mannan or maltose-substituted solid supports. Crystallographic analysis of the human neck + CRD complexed with maltotriose or p-nitrophenyl-maltoside showed stacking of the terminal glucose or nitrophenyl ring with the aromatic ring of Phe-335. Our studies indicate that Phe-335, which is evolutionarily conserved in all known SP-Ds, plays important, if not critical, roles in SP-D function.