9 research outputs found
O-mannosyl phosphorylation of alpha-dystroglycan is required for laminin binding.
Alpha-dystroglycan (alpha-DG) is a cell-surface glycoprotein that acts as a receptor for both extracellular matrix proteins containing laminin-G domains and certain arenaviruses. Receptor binding is thought to be mediated by a posttranslational modification, and defective binding with laminin underlies a subclass of congenital muscular dystrophy. Using mass spectrometry- and nuclear magnetic resonance (NMR)-based structural analyses, we identified a phosphorylated O-mannosyl glycan on the mucin-like domain of recombinant alpha-DG, which was required for laminin binding. We demonstrated that patients with muscle-eye-brain disease and Fukuyama congenital muscular dystrophy, as well as mice with myodystrophy, commonly have defects in a postphosphoryl modification of this phosphorylated O-linked mannose, and that this modification is mediated by the like-acetylglucosaminyltransferase (LARGE) protein. These findings expand our understanding of the mechanisms that underlie congenital muscular dystrophy
Structural basis of laminin binding to the LARGE glycans on dystroglycan
Dystroglycan is a highly glycosylated extracellular matrix receptor with essential functions in skeletal muscle and the nervous system. Reduced matrix binding by α-dystroglycan (α-DG) due to perturbed glycosylation is a pathological feature of several forms of muscular dystrophy. Like-acetylglucosaminyltransferase (LARGE) synthesizes the matrix-binding heteropolysaccharide [-glucuronic acid-β1,3-xylose- α1,3-]n. Using a dual exoglycosidase digestion, we confirm that this polysaccharide is present on native α-DG from skeletal muscle. The atomic details of matrix binding were revealed by a high-resolution crystal structure of laminin G-like (LG) domains 4-5 of laminin α2 bound to a LARGE-synthesized oligosaccharide. A single glucuronic acid- β1,3-xylose disaccharide repeat straddles a Ca2+ ion in the LG4 domain, with oxygen atoms from both sugars replacing Ca2+-bound water molecules. The chelating binding mode accounts for the high affinity of this protein-carbohydrate interaction. These results reveal a novel mechanism of carbohydrate recognition and provide a structural framework for elucidating the mechanisms underlying muscular dystrophy
Loss of α-Dystroglycan Laminin Binding in Epithelium-derived Cancers Is Caused by Silencing of LARGE*S⃞♦
The interaction between epithelial cells and the extracellular matrix is
crucial for tissue architecture and function and is compromised during cancer
progression. Dystroglycan is a membrane receptor that mediates interactions
between cells and basement membranes in various epithelia. In many
epithelium-derived cancers, β-dystroglycan is expressed, but
α-dystroglycan is not detected. Here we report that α-dystroglycan
is correctly expressed and trafficked to the cell membrane but lacks laminin
binding as a result of the silencing of the like-acetylglucosaminyltransferase
(LARGE) gene in a cohort of highly metastatic epithelial cell lines
derived from breast, cervical, and lung cancers. Exogenous expression of LARGE
in these cancer cells restores the normal glycosylation and laminin binding of
α-dystroglycan, leading to enhanced cell adhesion and reduced cell
migration in vitro. Our findings demonstrate that LARGE repression is
responsible for the defects in dystroglycan-mediated cell adhesion that are
observed in epithelium-derived cancer cells and point to a defect of
dystroglycan glycosylation as a factor in cancer progression