Smalheiser N R, Kim E
Department of Pediatrics, University of Chicago, Illinois 60637, USA.
J Biol Chem. 1995 Jun 23;270(25):15425-33. doi: 10.1074/jbc.270.25.15425.
Cranin was described in 1987 as a membrane glycoprotein expressed in brain and many other tissues, which binds laminin with high affinity in a calcium-dependent manner. Dystrophin-associated glycoprotein ("dystroglycan") is a laminin-binding protein cloned in 1992 whose relation to cranin has remained uncertain. Here we describe the purification of cranin to homogeneity from sheep brain, show cranin to be a form of dystroglycan, and localize the N terminus of beta-dystroglycan to amino acid residue 654. We find that brain alpha-dystroglycan is tightly associated with membranes, and localizes to regions of synaptic contact as assessed by immunocytochemistry of rat cerebellum. Brain alpha-dystroglycan expresses high mannose/hybrid N-linked saccharides, terminal GalNAc residues, and the HNK-1 epitope. Although dystroglycan has previously been presumed to be a proteoglycan, the amino acid sequence, pI, O-sialoglycoprotease susceptibility, lectin-binding profile, and laminin-binding properties of brain dystroglycan are more typical of mucin-like proteins. Furthermore, using CHO mutant cell lines deficient in xylosyltransferase and galactosyltransferase I, which are required for glycosaminoglycan biosynthesis, it is shown that chondroitin sulfate and heparan sulfate are not critical for laminin binding, and indeed are apparently not expressed at all in dystroglycan from CHO cells.
1987年，颅素被描述为一种在脑和许多其他组织中表达的膜糖蛋白，它以钙依赖的方式与层粘连蛋白高亲和力结合。抗肌萎缩蛋白相关糖蛋白（“抗肌萎缩蛋白聚糖”）是1992年克隆的一种层粘连蛋白结合蛋白，它与颅素的关系仍不确定。在此，我们描述了从羊脑中纯化出均一的颅素，证明颅素是抗肌萎缩蛋白聚糖的一种形式，并将β-抗肌萎缩蛋白聚糖的N端定位到氨基酸残基654。我们发现脑α-抗肌萎缩蛋白聚糖与膜紧密相关，并通过大鼠小脑的免疫细胞化学评估定位于突触接触区域。脑α-抗肌萎缩蛋白聚糖表达高甘露糖/杂合N-连接糖、末端N-乙酰半乳糖胺残基和HNK-1表位。尽管抗肌萎缩蛋白聚糖以前被认为是一种蛋白聚糖，但脑抗肌萎缩蛋白聚糖的氨基酸序列、pI、O-唾液酸糖蛋白酶敏感性、凝集素结合谱和层粘连蛋白结合特性更类似于粘蛋白样蛋白。此外，使用缺乏木糖基转移酶和半乳糖基转移酶I（糖胺聚糖生物合成所必需）的CHO突变细胞系，结果表明硫酸软骨素和硫酸乙酰肝素对层粘连蛋白结合并不关键，实际上在CHO细胞的抗肌萎缩蛋白聚糖中显然根本不表达。
