Victor Xylophone V, Nguyen Thao K N, Ethirajan Manivannan, Tran Vy M, Nguyen Khiem V, Kuberan Balagurunathan
Department of Medicinal Chemistry, University of Utah, Salt Lake City, Utah 84112, USA.
J Biol Chem. 2009 Sep 18;284(38):25842-53. doi: 10.1074/jbc.M109.043208. Epub 2009 Jul 23.
Glycosaminoglycan (GAG) biosynthesis requires numerous biosynthetic enzymes and activated sulfate and sugar donors. Although the sequence of biosynthetic events is resolved using reconstituted systems, little is known about the emergence of cell-specific GAG chains (heparan sulfate, chondroitin sulfate, and dermatan sulfate) with distinct sulfation patterns. We have utilized a library of click-xylosides that have various aglycones to decipher the mechanism of GAG biosynthesis in a cellular system. Earlier studies have shown that both the concentration of the primers and the structure of the aglycone moieties can affect the composition of the newly synthesized GAG chains. However, it is largely unknown whether structural features of aglycone affect the extent of sulfation, sulfation pattern, disaccharide composition, and chain length of GAG chains. In this study, we show that aglycones can switch not only the type of GAG chains, but also their fine structures. Our findings provide suggestive evidence for the presence of GAGOSOMES that have different combinations of enzymes and their isoforms regulating the synthesis of cell-specific combinatorial structures. We surmise that click-xylosides are differentially recognized by the GAGOSOMES to generate distinct GAG structures as observed in this study. These novel click-xylosides offer new avenues to profile the cell-specific GAG chains, elucidate the mechanism of GAG biosynthesis, and to decipher the biological actions of GAG chains in model organisms.
糖胺聚糖（GAG）生物合成需要多种生物合成酶以及活化的硫酸盐和糖供体。尽管使用重组系统已解析了生物合成事件的顺序，但对于具有不同硫酸化模式的细胞特异性GAG链（硫酸乙酰肝素、硫酸软骨素和硫酸皮肤素）的出现情况却知之甚少。我们利用了一系列具有不同苷元的点击木糖苷文库，来解读细胞系统中GAG生物合成的机制。早期研究表明，引物的浓度和苷元部分的结构都会影响新合成的GAG链的组成。然而，苷元的结构特征是否会影响GAG链的硫酸化程度、硫酸化模式、二糖组成和链长，在很大程度上尚不清楚。在本研究中，我们表明苷元不仅可以改变GAG链的类型，还能改变其精细结构。我们的研究结果为存在GAGOSOMES提供了暗示性证据，GAGOSOMES具有不同组合的酶及其同工型，可调节细胞特异性组合结构的合成。我们推测，如本研究中所观察到的，点击木糖苷被GAGOSOMES以不同方式识别，从而产生不同的GAG结构。这些新型点击木糖苷为分析细胞特异性GAG链、阐明GAG生物合成机制以及解读模型生物中GAG链的生物学作用提供了新途径。
