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Publication : Xylosyl- and glucuronyltransferase functions of LARGE in α-dystroglycan modification are conserved in LARGE2.

First Author  Inamori K Year  2013
Journal  Glycobiology Volume  23
Issue  3 Pages  295-302
PubMed ID  23125099 Mgi Jnum  J:215860
Mgi Id  MGI:5607213 Doi  10.1093/glycob/cws152
Citation  Inamori K, et al. (2013) Xylosyl- and glucuronyltransferase functions of LARGE in alpha-dystroglycan modification are conserved in LARGE2. Glycobiology 23(3):295-302
abstractText  LARGE-dependent modification enables alpha-dystroglycan (alpha-DG) to bind to its extracellular matrix ligands. Mutations in the LARGE gene and several others involved in O-mannosyl glycan synthesis have been identified in congenital and limb-girdle muscular dystrophies that are characterized by perturbed glycosylation and reduced ligand-binding affinity of alpha-DG. LARGE is a bifunctional glycosyltransferase that alternately transfers xylose and glucuronic acid, thereby generating the heteropolysaccharides on alpha-DG that confer its ligand binding. Although the LARGE paralog LARGE2 (also referred to as GYLTL1B) has likewise been shown to enhance the functional modification of alpha-DG in cultured cells, its enzymatic activities have not been identified. Here, we report that LARGE2 is also a bifunctional glycosyltransferase and compare its properties with those of LARGE. By means of a high-performance liquid chromatography-based enzymatic assay, we demonstrate that like LARGE, LARGE2 has xylosyltransferase (Xyl-T) and glucuronyltransferase (GlcA-T) activities, as well as polymerizing activity. Notably, however, the pH optima of the Xyl-T and GlcA-T of LARGE2 are distinct from one another and also from those of LARGE. Our results suggest that LARGE and LARGE2 catalyze the same glycosylation reactions for the functional modification of alpha-DG, but that they have different biochemical properties.
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