Molecular Dynamics Reveals a Glycan Conformation Underlying IDUA Dysfunction in Attenuated MPS I.

Mucopolysaccharidosis Type I (MPS I) is a rare autosomal recessive lysosomal storage disorder caused by mutations in α-ʟ-iduronidase (IDUA) enzyme, a glycosylated hydrolase responsible for glycosaminoglycan (GAG) degradation. Pathogenic variants are associated with a broad clinical spectrum, from severe Hurler syndrome to attenuated Scheie phenotype. The missense mutations L490P and P533R cause attenuated-intermediate MPS I, retaining residual enzyme activity. To investigate the structural mechanisms underlying these phenotypes, we performed all-atom molecular dynamics simulations -18 trajectories of 1.6 μs each- comparing wild type IDUA with L490P and P533R mutants at pH 7.5 and 4.5, mimicking the endoplasmic reticulum (ER) and lysosomal microenvironments, respectively. Backbone root-mean-square deviation and fluctuation analyses indicated that the overall protein fold was maintained across conditions; however, we identified a pH-dependent restricted conformational flexibility of the N372-linked glycan in both mutants. Cluster analysis performed on the obtained trajectories showed that both mutations affect the conformation of this glycan. Hydrogen bond analysis further revealed that P533R induces aberrant, persistent glycan-protein interactions, providing a possible structural explanation for reduced IDUA activity and, therefore, GAG processing. Our findings, supported by in vitro data, propose glycan conformational restriction as a possible new molecular mechanism that underpins enzymatic dysfunction in attenuated MPS I, opening new avenues for structure-informed therapeutic strategies.