Determination of the structure of human α-l-iduronidase and structural basis of mucopolysaccharidosis type Ι

Abstract

In this study, we tried to determine the crystal structure of human α-l-iduronidase (hIDUA) and elucidate the structural basis of mucopolysaccharidosis type I (MPS I). We crystallized and solved the structure of hIDUA by the single isomorphous replacement with anomalous scattering method. A deglycosylation study was performed to examine the involvement of N-glycan in the substrate interaction. Then, we built structural models of mutant hIDUA due to 57 amino acid substitutions that had been identified in 27 severe, 1 severeintermediate, 13 intermediate, 1 attenuated-intermediate and 15 attenuated type MPS I patients by means of homology modeling using the crystal hIDUA structure as a template. The structural changes were examined by calculating the root-mean-square distances (RMSDs) and the number of atoms influenced by the amino acid replacements. We solved the crystal structures of apoand iduronic acid -bound hIDUA consisting of three domains: a triosephosphate isomerase barrel fold, a β-sandwich domain and an immunoglobulin-like domain. The mannose residue of the N-glycan attached to N372 constituted a part of the substrate-binding pocket and interacted directly with a substrate. The result of deglycosylation study showed that the hIDUA enzyme activity was highly correlated with the N-glycan attached to N372. Structural analysis revealed that W306 interacts with the N-glycan at N372 and the W306L mutation may cause MPS I through the effect on the conformation of theN-glycan atN372. Further structural study revealed that the RMSD values and the numbers of atoms influenced by amino acid substitutions found in severeMPS I patients were larger than those in intermediate and attenuated MPS I ones, suggesting that the structural changes of hIDUA tended to be correlated with the severity of the disease. Coloring of atoms influenced by an amino acid substitution was performed in each case. On the basis of these results, we constructed a database and disclosed the structural information involving MPS I. Structural investigation is useful for elucidating the basis of MPS I.