Identification of novel bioactive glycans on dystroglycan

描述(由申请人提供)：营养不良多糖是一种细胞黏附分子，在神经肌肉和皮质发育以及肌肉营养不良症中发挥重要作用。营养不良多糖(ADG)的糖基化是其功能所必需的；已鉴定出六个基因，当突变时，会导致ADG糖基化不足，导致包括层粘连蛋白在内的细胞外基质蛋白结合减少或缺失。这些基因的缺陷也会导致各种形式的先天性肌营养不良症(CMD)，其中ADG糖基化不足是导致分子缺陷的原因。其中几个基因(POMT1、POMT2、POMGNT1)是糖基转移酶，参与ADG蛋白上O-连接甘露糖结构的合成。在哺乳动物中，O-连接的甘露糖只存在于ADG上。因此，这些碳水化合物结构对这一种蛋白质是高度特异的。另外三个已知的改变ADG糖基化的CMD基因的功能尚不清楚，尽管许多研究人员进行了大量的努力。其中一个是大的，在肌营养不良症(LARGEmyd)小鼠中缺失的基因。大基因之所以重要，不仅是因为该基因的缺陷会导致人类疾病，还因为它的过度表达已被证明可以刺激ADG的糖基化，并挽救CMD患者细胞中的层粘连蛋白结合。因此，了解大功能可能是发展治疗多种形式的CMD的关键，也是了解肌营养不良蛋白聚糖在神经肌肉发育中的作用的关键。在这里，我们提供的证据表明，大分子合成一种新的碳水化合物结构。这种结构，就像O-甘露糖一样，在哺乳动物中极其罕见，但在低等生物中很常见。这项提议将最终确定Dystroglan上这种碳水化合物结构的存在，定义它在配体结合中的作用，并将Large的功能定义为创建它的酶。因此，这一提议不仅定义了一种具有重要治疗意义的酶的新功能，而且可能识别出一种尚未在哺乳动物中描述的多糖结构。

DESCRIPTION (provided by applicant): Dystroglycan is a cell adhesion molecule that plays important roles in neuromuscular and cortical development and in muscular dystrophy. The glycosylation of a dystroglycan (aDG) is essential for its function; Six genes have been identified that, when mutated, cause the underglycosylation of aDG leading to diminished or absent binding of extracellular matrix proteins, including laminin. Defects in these genes also cause forms of congenital muscular dystrophy (CMD) where underglycosylation of aDG is causative molecular defect. Several of these genes (POMT1, POMT2, POMGnT1) are known to be glycosyltransferases involved in the synthesis of O-linked mannose structures on the aDG protein. In mammals, O-linked mannose has only been shown to exist on aDG. Thus, these carbohydrate structures are highly specific to this one protein. The functions of the three other known CMD genes that alter aDG glycosylation are unknown, despite intense efforts by numerous investigators. One of these is LARGE, the gene deleted in the myodystrophy (LARGEmyd) mouse. LARGE is important not only because defects in this gene cause human disease, but also because its overexpression has been shown to stimulate glycosylation of aDG and rescue laminin binding in cells from CMD patients. Thus, understanding LARGE function may be a key to the development of therapeutics for multiple forms of CMD as well as to understanding the role of dystroglycan in neuromuscular development. Here we provide evidence that suggests that LARGE synthesizes a novel carbohydrate structure. This structure, like O-mannose, appears to be extremely rare in mammals but common in lower organisms. This proposal will conclusively identify the presence of this carbohydrate structure on dystroglycan, define its role in ligand binding, and define the function of LARGE as the enzyme that creates it. This proposal, therefore, will not only define a novel function for a therapeutically important enzyme, but likely identify a glycan structure not yet described in mammals.