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.

中文翻译：

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HOIL-1 泛素连接酶活性靶向无支链葡糖，是防止聚葡聚糖积累所必需的。

HOIL-1 是线性泛素链组装复合体 (LUBAC) 的一个组成部分，通过酯化作用泛素化蛋白质中的丝氨酸和苏氨酸残基。在这里，我们报告说，表达 E3 连接酶失活 HOIL-1[C458S] 突变体的小鼠会在大脑、心脏和其他器官中积累聚葡聚糖，这表明 HOIL-1 的 E3 连接酶活性对于防止这些有毒多糖沉积物积累至关重要。我们发现 HOIL-1 在体外单泛素化糖原和 α1:4 连接的麦芽七糖，并将葡萄糖的 C6 羟基部分鉴定为酯连接的泛素化位点。通过 Met1 连接或 Lys63 连接的泛素寡聚体与 HOIL-1 的 RBR 结构域的相互作用，麦芽七糖的单泛素化加速了 > 100 倍。HOIL-1 还将预先形成的泛素低聚物整体转移到麦芽七糖中，在一个催化步骤中生产聚泛素化麦芽七糖。LUBAC 的 Sharpin 和 HOIP 成分，但不是 HOIL-1，在体外与无支链和不常支链的葡萄糖聚合物结合，但不与高度支化的哺乳动物糖原结合，表明 HOIL-1 靶向细胞中无支链葡萄糖的潜在功能。我们认为无支链葡糖的单泛素化可能会启动它们从细胞中去除，从而防止沉淀为聚葡聚糖。