<scp>RNF13</scp> is a previously undescribed interactor of iduronate 2‐sulfatase that modifies its glycosylation and maturation

Mucopolysaccharidosis type II, also known as Hunter syndrome, is a rare and fatal disease caused by mutations in the iduronate 2-sulfatase (IDS) encoding gene. Enzymatically inactive IDS variants lead to pathological accumulation of glycosaminoglycans in lysosomes, resulting in dysfunction of multiple organs. IDS is expressed as a precursor protein, and its proper processing and lysosomal targeting are crucial for enzymatic activity. However, the intracellular dynamics of IDS remain poorly understood, and a better understanding of its processing mechanisms would benefit the development of new therapeutic strategies. alphafold 3 predicted an interaction between IDS and the E3 ubiquitin ligase RNF13. Co-immunoprecipitation assays confirmed this interaction and further revealed that RNF13 preferentially interacts with a predominantly underglycosylated immature form of IDS, leading to altered IDS glycosylation and maturation. The results demonstrate that IDS glycosylation site Asn246 is important for lysosomal targeting, although its glycosylation is not altered by RNF13. Importantly, this study demonstrates that RNF13 forms a heterodimer with the E3 ubiquitin ligase RNF167, which modulates the lysosomal trafficking of both proteins. In addition, the heterodimer interacts and alters IDS processing differently than RNF13 or RNF167 alone. RNF13 catalytic E3 ligase activity is required to generate an underglycosylated form, but not that of RNF167. This study shows that the proteasome rapidly degrades IDS underglycosylated forms, and RNF13 exerts a protective effect. Overall, this study reveals a previously undescribed and dual role of RNF13 in IDS maturation and degradation, providing mechanistic insights into IDS trafficking.