HOIL‐1 ubiquitin ligase activity targets unbranched glucosaccharides and is required to prevent polyglucosan accumulation

• Published in: The EMBO journal Vol. 41; no. 8; pp. e109700 - n/a
• Main Authors: Kelsall, Ian R, McCrory, Elisha H, Xu, Yingqi, Scudamore, Cheryl L, Nanda, Sambit K, Mancebo‐Gamella, Paula, Wood, Nicola T, Knebel, Axel, Matthews, Stephen J, Cohen, Philip
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 19.04.2022; Blackwell Publishing Ltd; John Wiley and Sons Inc
• Subjects: Accumulation; Animals; Assembly; Brain; EMBO21; EMBO24; EMBO31; Esterification; Glucans; Glucose; Glycogen; Glycogen - metabolism; Glycogens; Mammals; Mice; Mutants; Mutation; NF-kappa B - metabolism; Oligomers; Organs; polyglucosan; Polymers; Polypeptides; Polysaccharides; Quality control; RBCK1; RBR E3 ligase; Threonine; Ubiquitin; Ubiquitin - metabolism; Ubiquitin-protein ligase; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism; Ubiquitination; RBR E3 ligase; glycogen; RBCK1; ubiquitination; polyglucosan
• ISSN: 0261-4189; 1460-2075
• DOI: 10.15252/embj.2021109700

HOIL‐1, a component of the linear ubiquitin chain assembly complex (LUBAC), ubiquitylates serine and threonine residues in proteins by esterification. Here, we report that mice expressing an E3 ligase‐inactive HOIL‐1[C458S] mutant accumulate polyglucosan in brain, heart and other organs, indicating that HOIL‐1’s E3 ligase activity is essential to prevent these toxic polysaccharide deposits from accumulating. We found that HOIL‐1 monoubiquitylates glycogen and α1:4‐linked maltoheptaose in vitro and identify the C6 hydroxyl moiety of glucose as the site of ester‐linked ubiquitylation. The monoubiquitylation of maltoheptaose was accelerated > 100‐fold by the interaction of Met1‐linked or Lys63‐linked ubiquitin oligomers with the RBR domain of HOIL‐1. HOIL‐1 also transferred pre‐formed ubiquitin oligomers to maltoheptaose en bloc , producing polyubiquitylated maltoheptaose in one catalytic step. The Sharpin and HOIP components of LUBAC, but not HOIL‐1, bound to unbranched and infrequently branched glucose polymers in vitro, but not to highly branched mammalian glycogen, suggesting a potential function in targeting HOIL‐1 to unbranched glucosaccharides in cells. We suggest that monoubiquitylation of unbranched glucosaccharides may initiate their removal from cells, preventing precipitation as polyglucosan. Synopsis Mutations in the linear ubiquitin chain assembly complex (LUBAC) component HOIL‐1, which can ubiquitylate hydroxyl side chains in polypeptides, are linked to toxic polyglucosan accumulation. Demonstration of glucosaccharide ubiquitylation by the HOIL‐1 E3 ligase suggests its involvement in a quality control mechanism that removes unbranched glycogen to prevent its precipitation as toxic polyglucosan deposits. HOIL‐1 in vitro monoubiquitylates the unbranched α1:4‐linked glucosaccharide maltoheptaose at the C6‐hydroxyl moiety of glucose. HOIL‐1‐catalysed monoubiquitylation of maltoheptaose is accelerated > 100‐fold by Met1‐linked or Lys63‐linked ubiquitin oligomers, which interact with the RBR domain of HOIL‐1. LUBAC components Sharpin and HOIP bind to unbranched and infrequently branched glucose polymers in vitro , but not to highly branched mammalian glycogen. Mice expressing an E3 ligase‐inactive mutant of HOIL‐1 accumulate polyglucosan in brain and other organs. Graphical Abstract Linear ubiquitin chain assembly complex (LUBAC) targeting and ubiquitin attachment to unbranched glucose polymers may prevent formation of toxic polyglucosan deposits in cells.