Science Independently confirmed 2 publishers 2 min read Published Sep 17, 2026, 11:19 PM PDT

A ubiquitin ligase tags malformed glycogen for disposal in the mouse brain

Researchers at Cambridge and the MRC Laboratory of Molecular Biology report in Nature that the enzyme RNF213 ubiquitylates poorly branched glycogen directly, and that mice without that ligase activity accumulate polyglucosan in three brain regions.

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Illustration accompanying A ubiquitin ligase tags malformed glycogen for disposal in the mouse brain — Generated illustration

What happened

Glycogen stays soluble because it is heavily branched, and when cells build it badly the sugar collapses into dense polyglucosan bodies that pile up inside brain cells and cause irreversible damage.
A Nature paper from Cambridge and the MRC Laboratory of Molecular Biology reports that the enzyme RNF213 attaches ubiquitin directly to defective glycogen, which triggers autophagy to break it down.
Mice whose RNF213 lacks ligase activity accumulated polyglucosan in the cerebellum, pons and hippocampus.
Cryo-EM of RNF213 bound to glycogen-derived maltoheptaose showed that the enzyme's CBM20 domain binds linear oligosaccharides.

Why it matters

What it limits constraint A drug here would have to raise the activity of a destructive enzyme without aiming it at the glucose store cells depend on, and the one manipulation that raised activity in this study did exactly that.
What's now possible capability The study's flow cytometry separates polyglucosan already inside lysosomes from polyglucosan still in the cytosol. A screen for compounds that speed clearance now has something quantitative to read.
What it sets up precedent Ubiquitin has been treated as a tag on proteins. A sugar substrate makes it reasonable to go looking for other non-protein targets and the ligases that mark them.

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Confirmed2 publishers

The CBM20 domain works as a limit. When the authors disrupted its carbohydrate binding, RNF213 gained ligase activity toward physiological glycogen ^[11]. The domain that lets the enzyme recognise abnormal sugar is also what keeps it off the cell's working glucose store. Anyone designing an activator inherits that arrangement.

"A few years ago, we found RNF213 ubiquitylates LPS on intracellular bacteria, marking them for destruction. It is remarkable to see the same enzyme fighting bacteria and policing glycogen," said senior author Felix Randow, director of research at the University of Cambridge's Department of Medicine and a group leader at the MRC Laboratory of Molecular Biology ^[15].

RNF213 is not alone on the job. Epistasis analysis places it upstream of LUBAC, which the authors read as a hierarchical network of several E3 ligases surveying glycogen quality ^[12]. Downstream, ubiquitylated polyglucosan recruits the autophagy receptors SQSTM1, TAX1BP1 and optineurin, and the deposits are then taken up into autophagosomes ^[13]. The paper places this quality control in astrocytes ^[14].

The broader claim is about ubiquitin itself, which has been studied mainly as a regulator of proteins and is here shown labelling a carbohydrate directly ^[8]. "We are beginning to realize that ubiquitylation extends far beyond proteins. It is exciting to see what new biological roles emerge in the future," said first author Matthew Yip, a postdoc in the Protein and Nucleic Acid Chemistry Division of the MRC Laboratory of Molecular Biology ^[4].

The animal evidence comes from mice, and the abnormal sugar in the cell experiments came from cells engineered to produce polyglucosan ^[3]. The published abstract does not report a human carrying an RNF213 variant alongside disease. Cambridge names Lafora disease and polyglucosan body myopathy as the conditions this pathway speaks to ^[19].

Lafora disease was identified in 1911 by the Spanish neurologist Gonzalo Rodríguez Lafora ^[6], which is 115 years before this paper appeared ^[17]. It typically begins in adolescence and progresses through severe seizures, rapid cognitive decline and loss of motor control, and it is ultimately fatal ^[16]. It remains incurable, and existing options only manage symptoms ^[6].

What to watch

Whether anyone reports human RNF213 loss-of-function variants in patients with polyglucosan body disease.
Whether raising RNF213 activity in mice clears deposits that have already formed, and whether it spares normal glycogen.
Whether LUBAC or another ligase in the hierarchy compensates when RNF213 ligase activity is removed.

Clarity's read

What the record supports and how the coverage leans. The claims behind it follow.

Reality

Evidence72
Adoption: Not scored
Hype gap+18
Incentives55
Confidence68

Why these scores

Claim ledger

Ranked by verification strength, evidence, and original report placement.

[1]
Researchers at the University of Cambridge and the MRC Laboratory of Molecular Biology, led by senior author Professor Felix Randow, reported the finding in Nature this week.
Reported SupportedView cited source
[2]
RNF213 attaches ubiquitin directly to defective glycogen molecules, and the tag acts as a disposal signal that triggers autophagy to break down the damaged energy stores.
Reported SupportedView cited source
[3]
Using cells engineered to produce polyglucosan, the authors show that RNF213 selectively ubiquitylates abnormal glycogen.
Reported SupportedView cited source
[4]
"We are beginning to realize that ubiquitylation extends far beyond proteins. It is exciting to see what new biological roles emerge in the future," said first author Matthew Yip, a postdoc in the Protein and Nucleic Acid Chemistry Division of the MRC Laboratory of Molecular Biology.
Reported SupportedView cited source
[5]
Glycogen is the main form in which cells store glucose, and its highly branched structure keeps it soluble; when cells assemble it incorrectly or quality control fails, the sugar becomes poorly branched and settles into dense insoluble clumps called polyglucosan bodies, which accumulate inside brain cells and cause irreversible tissue damage.
Reported SupportedView cited source
[6]
Lafora disease was first identified in 1911 by the Spanish neurologist Gonzalo Rodriguez Lafora, and the condition remains incurable, with existing options only managing symptoms.
Reported SupportedView cited source
[7]
The paper is Yip, M.C.J., Naydenova, K., Otten, E.G. et al., 'Quality control of glycogen through direct ubiquitylation by RNF213', Nature (2026), DOI 10.1038/s41586-026-11139-6.
Reported SupportedView cited source
[8]
The findings reveal that ubiquitin, previously known mainly for regulating proteins, can directly label carbohydrates such as glycogen.
Reported SupportedView cited source
[9]
Mice lacking ligase activity in RNF213 accumulate polyglucosan in the cerebellum, pons and hippocampus.
Reported SupportedView cited source
[10]
Cryo-EM analysis of RNF213 bound to glycogen-derived maltoheptaose revealed that its CBM20 domain binds linear oligosaccharides.
Reported SupportedView cited source
[11]
Disrupting carbohydrate binding results in gain of E3 ligase activity towards physiological glycogen, indicating that the CBM20 domain limits RNF213 activity towards physiological glycogen.
Reported SupportedView cited source
[12]
Epistasis analysis places RNF213 upstream of LUBAC, suggesting a hierarchical network of multiple E3 ligases surveying glycogen quality.
Reported SupportedView cited source
[13]
Ubiquitylated polyglucosan recruits the autophagy receptors SQSTM1, TAX1BP1 and optineurin, thereby triggering uptake into autophagosomes.
Reported SupportedView cited source
[14]
The findings identify RNF213 as a quality control factor preventing polyglucosan accumulation in astrocytes.
Reported SupportedView cited source
[15]
"A few years ago, we found RNF213 ubiquitylates LPS on intracellular bacteria, marking them for destruction. It is remarkable to see the same enzyme fighting bacteria and policing glycogen," said senior author Professor Randow, director of research at the Department of Medicine at the University of Cambridge and group leader at the MRC Laboratory of Molecular Biology.
Reported SupportedView cited source
[16]
Lafora disease typically begins in adolescence and triggers progressively severe seizures, rapid cognitive decline and loss of motor control, and is ultimately fatal.
Reported SupportedView cited source
[17]
The 1911 identification of Lafora disease preceded this Nature paper by 115 years.
Derived Supported
[18]
The study's supplementary material describes a flow cytometry gating strategy to distinguish lysosomal from cytosolic polyglucosan: cells positive for a Cy5-labelled glycogen probe are gated and Halo-TMR labelling efficiency is then analysed, and because TMR labelling is inefficient in acidified autophagosomes, signal intensity per cell reflects the amount of cytosolic polyglucosan.
Reported SupportedView cited source
[19]
Understanding this cleanup pathway is described as important for addressing rare genetic disorders such as Lafora disease and polyglucosan body myopathy.
Reported InsufficientView cited source

Sources

2 independent publishers whose own reporting we read for this story.

nature.com
1 article · September 14, 2026
Quality control of glycogen through direct ubiquitylation by RNF213
phys.org
1 article · September 17, 2026
Ubiquitin marks abnormal glycogen for destruction to protect the brain, study finds

Clarity analysis

How the coverage leans and what the record actually supports. Read the methodology

Perspective Coverage

How much of the coverage speaks to builders, operators and investors. It measures emphasis, not whether the story is right.

Builder

Nature's abstract carries the whole mechanism in six sentences. Mice with the ligase activity knocked out accumulate polyglucosan in cerebellum, pons and hippocampus. In cells engineered to make polyglucosan, RNF213 tags the abnormal sugar and leaves normal glycogen alone. A cryo-EM structure with a seven-sugar glycogen fragment puts the binding on the CBM20 domain, and breaking that binding makes the enzyme start ubiquitylating healthy glycogen too. The last result is the informative one for anyone building on this: the sugar-binding domain works as a brake on the ligase. Everything past the abstract is behind Nature's subscription page, so the one piece of method on view is the supplementary caption explaining how Halo-TMR labelling efficiency separates cytosolic polyglucosan from the acidified autophagosome pool. Phys.org describes the same finding without the domain names or the LUBAC ordering.

Operator

The evidence stops at a mouse brain and cultured astrocytes, and neither account describes a compound, a dose or a trial. Phys.org supplies the clinical stakes: Lafora disease typically begins in adolescence, brings progressively severe seizures, rapid cognitive decline and loss of motor control, and is ultimately fatal. What Randow's group adds is a reason the deposits form and a named set of autophagy receptors that recognise the tag. For a rare-disease programme that is a target and a readout, both several steps short of a patient.

Investor

Nature and Phys.org both skip any mention of a funder, a licence holder or a company working on polyglucosan clearance. What is on offer is a target with a structural handle: the CBM20 domain decides whether RNF213 attacks abnormal glycogen or all of it, and the diseases in question, Lafora disease and polyglucosan body myopathy, have no approved treatment after more than a century. Anything past that, including who owns the chemistry, would have to come from outside this reporting.