N-terminal domain on dystroglycan enables LARGE1 to extend matriglycan on α-dystroglycan and prevents muscular dystrophy

Abstract

Dystroglycan (DG) requires extensive post-translational processing and O-glycosylation to function as a receptor for extracellular matrix (ECM) proteins containing laminin-G-like (LG) domains. Matriglycan is an elongated polysaccharide of alternating xylose (Xyl) and glucuronic acid (GlcA) that binds with high-affinity to ECM proteins with LG-domains and is uniquely synthesized on α-dystroglycan (α-DG) by like-acetylglucosaminyltransferase-1 (LARGE1). Defects in the post-translational processing or O-glycosylation of α-DG that result in a shorter form of matriglycan reduce the size of α-DG and decrease laminin binding, leading to various forms of muscular dystrophy. Previously, we demonstrated that Protein O-Mannose Kinase (POMK) is required for LARGE1 to generate full-length matriglycan on α-DG (~150-250 kDa) (Walimbe et al., 2020). Here, we show that LARGE1 can only synthesize a short, non-elongated form of matriglycan in mouse skeletal muscle that lacks the DG N-terminus (α-DGN), resulting in a ~100-125 kDa α-DG. This smaller form of α-DG binds laminin and maintains specific force but does not prevent muscle pathophysiology, including reduced force production after eccentric contractions or abnormalities in the neuromuscular junctions. Collectively, our study demonstrates that α-DGN, like POMK, is required for LARGE1 to extend matriglycan to its full mature length on α-DG and thus prevent muscle pathophysiology.

Identification of a short, single site matriglycan that maintains neuromuscular function in the mouse

“…LARGE1 activity may be increased by molecular recognition of DG-Nt and the phosphate on coreM3, thereby explaining the existence of very long matriglycans ( 11 , 48 , 49 ). If the observed 80 Da modification corresponds to a phosphate on an O -mannose (see Fig.2 ), it is likely the extra mannose-phosphate can further boost LARGE activity.…”

The underlying mechanisms of arenaviral entry through matriglycan

“…There seems to be preferential binding of certain laminin isoforms, like laminin 10/11, to shorter lengths of matriglycan ( McDearmon et al, 2006 ). The ECM binding partners of matriglycan are effectively determined by their affinity to a specific polysaccharide length, where K D values range between 1–100 nM ( Goddeeris et al, 2013 ; Sciandra et al, 2013 ; Okuma et al, 2023 ). Thus, α-DG in particular tissues will have its preferred LG-domain containing ECM receptors.…”

“…The synthesis of full-length matriglycan is dependent upon LARGE1 recognition of the phosphorylation of the M3 glycan ( Walimbe et al, 2020 ). LARGE1 must also be properly oriented through specific binding to the N-terminal domain of α-DG ( Kanagawa et al, 2004 ; Fujimura et al, 2005 ; Okuma et al, 2023 ). Upon the sequential addition of β1,4-Xyl and β1,4-GlcA, by priming enzymes TMEM5 ( Manya et al, 2016 ; Praissman et al, 2016 ) and B4GAT1 ( Praissman et al, 2014 ; Willer et al, 2014 ), respectively, to the M3 core substrate, LARGE1 can initiate matriglycan synthesis ( Sheikh et al, 2017 ; Endo, 2019 ).…”

Identification of Matriglycan by Dual Exoglycosidase Digestion of α-Dystroglycan

“…We have routinely used this method to identify matriglycan and found it to be robust and reproducible ( Okuma et al, 2023 ; Briggs et al, 2016 ; Sheikh et al, 2020 ; Walimbe et al, 2020 ). Additional data validating our method is provided in Figure 1 and Figure 2 .…”