LARGE2-dependent glycosylation confers laminin-binding ability on proteoglycans

• Published in: Glycobiology (Oxford) Vol. 26; no. 12; pp. 1284 - 1296
• Main Authors: Inamori, Kei-Ichiro, Beedle, Aaron M, de Bernabé, Daniel Beltrán-Valero, Wright, Michael E, Campbell, Kevin P
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01-12-2016
• Subjects: Animals; Binding Sites; Embryonic Stem Cells - metabolism; Glycosylation; Glycosyltransferases - chemistry; Glycosyltransferases - metabolism; Laminin - chemistry; Laminin - metabolism; Mice; Mice, Knockout; Original articles; Proteoglycans - chemistry; Proteoglycans - metabolism; dystroglycan, glycosaminoglycan, laminin binding, LARGE2, proteoglycan
• ISSN: 0959-6658; 1460-2423
• DOI: 10.1093/glycob/cww075

Both LARGE1 (formerly LARGE) and its paralog LARGE2 are bifunctional glycosyltransferases with xylosy- and glucuronyltransferase activities, and are capable of synthesizing polymers composed of a repeating disaccharide [-3Xylα1,3GlcAβ1-]. Post-translational modification of the O-mannosyl glycan of α-dystroglycan (α-DG) with the polysaccharide is essential for it to act as a receptor for ligands in the extracellular matrix (ECM), and both LARGE paralogs contribute to the modification in vivo. LARGE1 and LARGE2 have different tissue distribution profiles and enzymatic properties; however, the functional difference of the homologs remains to be determined, and α-DG is the only known substrate for the modification by LARGE1 or LARGE2. Here we show that LARGE2 can modify proteoglycans (PGs) with the laminin-binding glycan. We found that overexpression of LARGE2, but not LARGE1, mediates the functional modification on the surface of DG
, Pomt1
and Fktn
embryonic stem cells. We identified a heparan sulfate-PG glypican-4 as a substrate for the LARGE2-dependent modification by affinity purification and subsequent mass spectrometric analysis. Furthermore, we showed that LARGE2 could modify several additional PGs with the laminin-binding glycan, most likely within the glycosaminoglycan (GAG)-protein linkage region. Our results indicate that LARGE2 can modify PGs with the GAG-like polysaccharide composed of xylose and glucuronic acid to confer laminin binding. Thus, LARGE2 may play a differential role in stabilizing the basement membrane and modifying its functions by augmenting the interactions between laminin globular domain-containing ECM proteins and PGs.