title: Xylosyl- and glucuronyltransferase functions of LARGE in α-dystroglycan modification are conserved in LARGE2.
abstract: LARGE-dependent modification enables α-dystroglycan (α-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 α-DG. LARGE is a bifunctional glycosyltransferase that alternately transfers xylose and glucuronic acid, thereby generating the heteropolysaccharides on α-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 α-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 α-DG, but that they have different biochemical properties.
authors.affiliation: Howard Hughes Medical Institute, University of Iowa Roy J. and Lucille A. Carver College of Medicine, Iowa City, IA 52242-1101, USA.
authors.forename: Kei-ichiro
authors.initials: K
authors.lastname: Inamori
authors.forename: Yuji
authors.initials: Y
authors.lastname: Hara
authors.forename: Tobias
authors.initials: T
authors.lastname: Willer
authors.forename: Mary E
authors.initials: ME
authors.lastname: Anderson
authors.forename: Zihan
authors.initials: Z
authors.lastname: Zhu
authors.forename: Takako
authors.initials: T
authors.lastname: Yoshida-Moriguchi
authors.forename: Kevin P
authors.initials: KP
authors.lastname: Campbell
mesh_terms: D000818:Animals; D016466:CHO Cells; D020134:Catalytic Domain; D006224:Cricetinae; D003412:Cricetulus; D049030:Dystroglycans / Q000378:metabolism*; D020723:Glucuronic Acid / Q000378:metabolism; D016695:Glycosyltransferases / Q000737:chemistry / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D051379:Mice; D017351:N-Acetylglucosaminyltransferases / Q000737:chemistry / Q000378:metabolism*; D055503:Protein Multimerization; D014994:Xylose / Q000378:metabolism
chemical_list: D049030:Dystroglycans; D020723:Glucuronic Acid; D014994:Xylose; D016695:Glycosyltransferases; C502747:Large1 protein, mouse; C507407:Large2 protein, mouse; D017351:N-Acetylglucosaminyltransferases