Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602, USA.
Department of Molecular Physiology and Biophysics, Department of Neurology, Howard Hughes Medical Institute, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, IA 52242, USA.
Glycobiology. 2020 Sep 28;30(10):817-829. doi: 10.1093/glycob/cwaa024.
Mutations in multiple genes required for proper O-mannosylation of α-dystroglycan are causal for congenital/limb-girdle muscular dystrophies and abnormal brain development in mammals. Previously, we and others further elucidated the functional O-mannose glycan structure that is terminated by matriglycan, [(-GlcA-β3-Xyl-α3-)n]. This repeating disaccharide serves as a receptor for proteins in the extracellular matrix. Here, we demonstrate in vitro that HNK-1 sulfotransferase (HNK-1ST/carbohydrate sulfotransferase) sulfates terminal glucuronyl residues of matriglycan at the 3-hydroxyl and prevents further matriglycan polymerization by the LARGE1 glycosyltransferase. While α-dystroglycan isolated from mouse heart and kidney is susceptible to exoglycosidase digestion of matriglycan, the functional, lower molecular weight α-dystroglycan detected in brain, where HNK-1ST expression is elevated, is resistant. Removal of the sulfate cap by a sulfatase facilitated dual-glycosidase digestion. Our data strongly support a tissue specific mechanism in which HNK-1ST regulates polymer length by competing with LARGE for the 3-position on the nonreducing GlcA of matriglycan.
多种基因的突变是导致α- 肌营养不良聚糖正确 O- 甘露糖化所必需的，这些突变是先天性/肢体带肌营养不良症和哺乳动物大脑发育异常的原因。以前，我们和其他人进一步阐明了功能 O-甘露糖聚糖结构，其末端是基质聚糖，[（-GlcA-β3-Xyl-α3-）n]。这个重复的二糖作为细胞外基质中蛋白质的受体。在这里，我们在体外证明 HNK-1 唾液酸转移酶（HNK-1ST/碳水化合物唾液酸转移酶）在基质聚糖的 3- 羟基硫酸化末端葡萄糖醛酸残基，并通过 LARGE1 糖基转移酶防止进一步的基质聚糖聚合。虽然从小鼠心脏和肾脏中分离的α- 肌营养不良聚糖容易受到基质聚糖外糖苷酶的消化，但在大脑中检测到的功能性、低分子量的α- 肌营养不良聚糖是有抵抗力的，而大脑中 HNK-1ST 的表达水平升高。用硫酸酯酶去除硫酸盐帽可促进双糖苷酶消化。我们的数据强烈支持一种组织特异性机制，即 HNK-1ST 通过与 LARGE 竞争基质聚糖非还原 GlcA 的 3- 位来调节聚合物长度。
