Difference in the binding mode of two mannose-binding proteins: demonstration of a selective minicluster effect.
Difference in the binding mode of two mannose-binding proteins: demonstration of a selective minicluster effect.
复制标题
两种甘露糖结合蛋白的结合模式的差异：选择性微簇效应的证明。
作者：
Quesenberry,MS;Lee,RT;Lee,YC
血清型和肝型甘露糖结合蛋白（MBP）均存在于高等动物中，均由碳水化合物识别结构域（CRD）和胶原结构域组成。虽然被称为甘露糖结合蛋白，这些蛋白质结合N-乙酰葡糖胺和其他相关的糖相当好。使用来自大鼠的两种类型MBP的克隆CRD部分的早期特异性研究[查尔兹，R. A.、Feizi，T.，Yuen，C.- T.，Drickamer，K.，& Quesenberry，M.（1990）J.Biol.Chem.265，20770 - 20777]揭示了肝MBP CRD结合N-糖苷的三甘露糖基核心结构，而血清MBP CRD不结合。我们研究了这些CRD使用固相和液相分析，测试单糖，糖蛋白和合成簇配体的基板的偏好。虽然有两个CRD的单糖结合特异性没有显着差异，他们表现出非常不同的天然糖蛋白和含甘露糖的簇糖苷的亲和力。最有趣的是，具有两个末端GlcNAc部分的合成簇配体对两种CRD具有与单价GlcNAc配体相等的亲和力，而一系列结构相似的Man封端的二价配体仅对肝CRD显示约20倍增强的亲和力。一个合理的解释是，肝脏MBP CRD每个亚基有两个糖结合位点，其中一个仅结合甘露糖，另一个结合甘露糖和N-乙酰葡糖胺。相反，血清MBP CRD只有一个后一种类型的网站。等温滴定量热法的结果支持这一假设。
Serum-type and liver-type mannose-binding proteins (MBP) are both present in higher animals and both are composed of a carbohydrate-recognition domain (CRD) and a collagenous domain. Although known as mannose-binding proteins, these proteins bindN-acetylglucosamine and other related sugars quite well. An earlier specificity study using cloned CRD portions of both types of MBP from rat [Childs, R. A., Feizi, T., Yuen, C.-T., Drickamer, K., & Quesenberry, M. (1990)J. Biol. Chem.265, 20770−20777] revealed that the liver MBP CRD binds the trimannosyl core structure ofN-glycosides, whereas the serum MBP CRD does not. We studied the substrate preferences of these CRDs using both solid and solution phase assays, testing monosaccharides, glycoproteins, and synthetic cluster ligands. While there was no significant difference in the monosaccharide binding specificities of the two CRDs, they displayed very different affinities for natural glycoproteins and mannose-containing cluster glycosides. Most interestingly, synthetic cluster ligands with two terminal GlcNAc moieties have affinity equal to monovalent GlcNAc ligands toward both CRDs, whereas a series of structurally similar Man-terminated divalent ligand displays about 20-fold enhanced affinity toward liver CRD only. A plausible explanation is that the liver MBP CRD has two sugar binding sites per subunit, one of which binds only mannose, and the other, both mannose andN-acetylglucosamine. In contrast, the serum MBP CRD has only one site of the latter type. Results of isothermal titration calorimetry support this hypothesis.