title: HNK-1 sulfotransferase-dependent sulfation regulating laminin-binding glycans occurs in the post-phosphoryl moiety on α-dystroglycan.
abstract: Dystroglycan (DG) is a cell surface glycoprotein that connects extracellular matrix molecules to the intracellular cytoskeleton, functioning as mechanical and signaling axes in various physiological events. Since the ligand-binding activity of DG strictly depends on O-mannosyl glycans attached to its extracellular α-DG subunit, aberrant glycosylation causes dystroglycanopathy, a subclass of congenital muscular dystrophy. Accumulating evidence shows that like-acetylglucosaminyltransferase (LARGE), a glycosyltransferase involved in the biosynthesis of a phosphodiester-linked modification on O-mannose, is essential for α-DG to gain the ligand-binding activity. We previously reported that human natural killer-1 sulfotransferase (HNK-1ST), which was originally reported as one of the enzymes responsible for HNK-1 glycoepitope, had an ability to suppress the glycosylation and the function of α-DG. In this study, we investigated how HNK-1ST regulates the glycosylation of α-DG using deletion and mutation analyses. We generated an α-DG mutant which has only one threonine residue capable of being modified by LARGE. Focusing on the single post-phosphoryl modification site, we found that HNK-1ST showed an almost complete inhibition of the LARGE-dependent modification and transferred a sulfate group to the phosphodiester-linked moiety on O-mannose. Furthermore, using an in vitro enzymatic assay system, we demonstrated that the sulfated α-DG by HNK-1ST is no longer glycosylated by LARGE. These results illustrate one possible glycosylation pathway where α-DG function is regulated by opposing actions of HNK-1ST and LARGE.
authors.affiliation: Department of Biological Chemistry, Human Health Sciences, Graduate School of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Nakagawa
authors.forename: Hiromu
authors.initials: H
authors.lastname: Takematsu
authors.forename: Shogo
authors.initials: S
authors.lastname: Oka
mesh_terms: D001665:Binding Sites; D049030:Dystroglycans / Q000378:metabolism*; D006801:Humans; D007797:Laminin / Q000378:metabolism*; D011134:Polysaccharides / Q000378:metabolism*; D015238:Sulfotransferases / Q000378:metabolism*
chemical_list: D007797:Laminin; D011134:Polysaccharides; D049030:Dystroglycans; C109318:HNK-1 sulfotransferase; D015238:Sulfotransferases
keywords: HNK-1ST; LARGE; laminin-binding glycan; sulfation; α-dystroglycan