Sugar ubiquitylation; a new surveillance mechanism recognising and eliminating misfolded macromolecules?

Human HOIL-1 deficiency leads to the accumulation of unbranched glucosaccharides in muscles and other tissues that lack the alpha1:6 branch points present in normally branched glycogen. These molecules precipitate in cells as insoluble deposits termed Polyglucosan Bodies (PB), causing cardiomyopathy and heart failure in young adults. We discovered that HOIL-1 is an atypical E3 ubiquitin ligase that ubiquitylates the hydroxyl side chains of serine and threonine residues in proteins forming ester bonds (Kelsall et al, 2019, Proc Natl. Acad Sci USA mice 116, 13293-13298). More recently, we found that micein which HOIL-1 had been replaced by an E3-ligase inactive mutant accumulate PB in the heart, brain and other tissues. We also found HOIL-1 can ubiquitylate unbranched glucosaccharides at the C6 hydroxyl group of glucose in vitro and that the ubiquitylation of this sugar was greatly enhanced by HOIP (HOIL-1-interacting protein) (Kelsall et al, 2022, EMBO J. 41:e109700). These findings led us to propose the hypothesis that one of the roles of HOIL-1 in mammalian cells is to ubiquitylate unbranched glucosaccharides formed by errors of metabolism, marking them for elimination by glycophagy, a process analogous to autophagy in which the ubiquitylated glucosaccharides are taken up into lysosomes where they are hydrolysed by the lysosomal alpha1:4 glucosidase, before they precipitate in the cytosol as toxic PB. If this hypothesis is correct, The aim of the project is to establish whether this hypothesis is correct, which would establish sugar ubiquitylation as a novel quality control mechanism and open-up a new aspect of ubiquitin biology.

We have been awarded one of the inaugural UKRI Pioneer Awards to test our hypothesis. The initial goals of the project are to develop cell lines in which the formation of unbranched glucosaccharides is accelerated but glycophagy is inhibited, leading to the accumulation of ubiquitylated unbranched glycogen, which can then be isolated and analysed to establish whether ubiquitylation of glycogen does indeed take place in cells. In the longer term, the goal will be to identify further examples of sugar ubiquitylation and their functions in other biological systems.

The position is for one year and would be suitable for scientists with research experience in one or more of the following:- protein chemistry, protein ubiquitylation, autophagy, glycogen metabolism or glycogen storage diseases.

Candidates must have a PhD and experience of biochemical techniques used in the study of either protein ubiquitylation, autophagy or glycogen metabolism. The position will be an opportunity for candidates to broaden their skillset by working in a well-funded lab using state-of-the-art technologies. Many of the scientists trained in this lab have subsequently gained international reputations in the field of cell regulation.

Your priorities will include:

• developing cell lines in which the formation of unbranched glycogen is accelerated and glycophagy is inhibited, and then exploiting them to isolate and identify ubiquitylated unbranched glycogen
• Preparation of results for publication
• Interacting with other lab members and collaborators
• Maintenance of meticulous lab records

Who we’re looking for:

Enthusiastic candidates who must have completed a PhD in a relevant area

• A passion for research on ubiquitylation and cellular quality control mechanisms
• Experience in biochemical methods involved in studying one or more of the following:- proteins, ubiquitylation, autophagy, glycogen metabolism
• Experience in immunoblotting and proteomics.

This contract is for a fixed term period of one year.