Synthesis of Uronic Acid 1-Azasugars as Putative Inhibitors of α-Iduronidase, ß-Glucuronidase and Heparanase.

1-Azasugar analogues of l-iduronic acid (l-IdoA) and d-glucuronic acid (d-GlcA) and their corresponding enantiomers have been synthesized as potential pharmacological chaperones for mucopolysaccharidosis I (MPS I), a lysosomal storage disease caused by mutations in the gene encoding α-iduronidase (IDUA). The compounds were efficiently synthesized in nine or ten steps from d- or l-arabinose, and the structures were confirmed by X-ray crystallographic analysis of key intermediates. All compounds were inactive against IDUA, although l-IdoA-configured 8 moderately inhibited ß-glucuronidase (ß-GLU). The d-GlcA-configured 9 was a potent inhibitor of ß-GLU and a moderate inhibitor of the endo-ß-glucuronidase heparanase. Co-crystallization of 9 with heparanase revealed that the endocyclic nitrogen of 9 forms close interactions with both the catalytic acid and catalytic nucleophile.

c.1898C>G/p.Ser633Trp Mutation in Alpha-L-Iduronidase: Clinical and Structural Implications.

Mucopolysaccharidosis type I is a rare autosomal recessive genetic disease caused by deficient activity of α-L-iduronidase. As a consequence of low or absent activity of this enzyme, glycosaminoglycans accumulate in the lysosomal compartments of multiple cell types throughout the body. Mucopolysaccharidosis type I has been classified into 3 clinical subtypes, ranging from a severe Hurler form to the more attenuated Hurler-Scheie and Scheie phenotypes. Over 200 gene variants causing the various forms of mucopolysaccharidosis type I have been reported. DNA isolated from dried blood spot was used to sequencing of all exons of the IDUA gene from a patient with a clinical phenotype of severe mucopolysaccharidosis type I syndrome. Enzyme activity of α-L-iduronidase was quantified by fluorimetric assay. Additionally, a molecular dynamics simulation approach was used to determine the effect of the Ser633Trp mutation on the structure and dynamics of the α-L-iduronidase. The DNA sequencing analysis and enzymatic activity shows a c.1898C>G mutation associated a patient with a homozygous state and α-L-iduronidase activity of 0.24 µmol/L/h, respectively. The molecular dynamics simulation analysis shows that the p.Ser633Trp mutation on the α-L-iduronidase affect significant the temporal and spatial properties of the different structural loops, the N-glycan attached to Asn372 and amino acid residues around the catalytic site of this enzyme. Low enzymatic activity observed for p.Ser633Trp variant of the α-L-iduronidase seems to lead to severe mucopolysaccharidosis type I phenotype, possibly associated with a perturbation of the structural dynamics in regions of the enzyme close to the active site.

Identification of a novel compound heterozygous IDUA mutation underlies Mucopolysaccharidoses type I in a Chinese pedigree.

BACKGROUND: Mucopolysaccharidosis type I (MPS I) is a rare autosomal storage disorder resulting from the defective alpha-L-iduronidase (encoded by IDUA) enzyme activity and accumulation of glycosaminoglycans (GAGs) in lysosomes. So far, more than 100 IDUA causative mutations have been identified leading to three MPS I phenotypic subtypes: Hurler syndrome (severe form), Hurler/Scheie syndrome (intermediate form), and Scheie syndrome (mild form). METHODS: Whole-exome sequencing (WES) was performed to identify the underlying genetic mutations. To verify the identified variations, Sanger sequencing was performed for all available family members following PCR amplification. The impact on IDUA protein was analyzed by sequential analysis and homology modeling. RESULTS: A novel IDUA heterozygous single base insertion (c.1815dupT, p.V606Cfs51* ) and a known missence mutation (c.T1037G, p.L346R) were detected in our patient diagnosed as congenital heart disease with heart valve abnormalities. The novel frameshift mutation results in a complete loss of 48 amino acids in the Ig-like domain and causes the formation of a putative protein product which might affect the IDUA enzyme activity. CONCLUSIONS: A novel compound heterozygous IDUA mutation (c.1815dupT, p.V606Cfs51* ) was found in a Chinese MPS I family. The identification of the mutation facilitated accurate genetic counseling and precise medical intervention for MPS I in China.

Brassica rapa hairy root based expression system leads to the production of highly homogenous and reproducible profiles of recombinant human alpha-L-iduronidase.

The Brassica rapa hairy root based expression platform, a turnip hairy root based expression system, is able to produce human complex glycoproteins such as the alpha-L-iduronidase (IDUA) with an activity similar to the one produced by Chinese Hamster Ovary (CHO) cells. In this article, a particular attention has been paid to the N- and O-glycosylation that characterize the alpha-L-iduronidase produced using this hairy root based system. This analysis showed that the recombinant protein is characterized by highly homogeneous post translational profiles enabling a strong batch to batch reproducibility. Indeed, on each of the 6 N-glycosylation sites of the IDUA, a single N-glycan composed of a core Man3 GlcNAc2 carrying one beta(1,2)-xylose and one alpha(1,3)-fucose epitope (M3XFGN2) was identified, highlighting the high homogeneity of the production system. Hydroxylation of proline residues and arabinosylation were identified during O-glycosylation analysis, still with a remarkable reproducibility. This platform is thus positioned as an effective and consistent expression system for the production of human complex therapeutic proteins.

N-glycan structures and downstream mannose-phosphorylation of plant recombinant human alpha-L-iduronidase: toward development of enzyme replacement therapy for mucopolysaccharidosis I.

KEY MESSAGE: Arabidopsis N-glycan processing mutants provide the basis for tailoring recombinant enzymes for use as replacement therapeutics to treat lysosomal storage diseases, including N-glycan mannose phosphorylation to ensure lysosomal trafficking and efficacy. Functional recombinant human alpha-L-iduronidase (IDUA; EC 3.2.1.76) enzymes were generated in seeds of the Arabidopsis thaliana complex-glycan-deficient (cgl) C5 background, which is deficient in the activity of N-acetylglucosaminyl transferase I, and in seeds of the Arabidopsis gm1 mutant, which lacks Golgi α-mannosidase I (GM1) activity. Both strategies effectively prevented N-glycan maturation and the resultant N-glycan structures on the consensus sites for N-glycosylation of the human enzyme revealed high-mannose N-glycans of predominantly Man5 (cgl-IDUA) or Man6-8 (gm1-IDUA) structures. Both forms of IDUA were equivalent with respect to their kinetic parameters characterized by cleavage of the artificial substrate 4-methylumbelliferyl-iduronide. Because recombinant lysosomal enzymes produced in plants require the addition of mannose-6-phosphate (M6P) in order to be suitable for lysosomal delivery in human cells, we characterized the two IDUA proteins for their amenability to downstream in vitro mannose phosphorylation mediated by a soluble form of the human phosphotransferase (UDP-GlcNAc: lysosomal enzyme N-acetylglucosamine [GlcNAc]-1-phosphotransferase). Gm1-IDUA exhibited a slight advantage over the cgl-IDUA in the in vitro M6P-tagging process, with respect to having a better affinity (i.e. lower K m) for the soluble phosphotransferase. This may be due to the greater number of mannose residues comprising the high-mannose N-glycans of gm1-IDUA. Our elite cgl- line produces IDUA at > 5.7% TSP (total soluble protein); screening of the gm1 lines showed a maximum yield of 1.5% TSP. Overall our findings demonstrate the relative advantages and disadvantages associated with the two platforms to create enzyme replacement therapeutics for lysosomal storage diseases.

Subcutaneous implantation of microencapsulated cells overexpressing α-L-iduronidase for mucopolysaccharidosis type I treatment.

Mucopolysaccharidosis type I (MPS I) is caused by a deficiency of α-L-iduronidase (IDUA), resulting in accumulation of glycosaminoglycans (GAG) in lysosomes. Microencapsulation of recombinant cells is a promising gene/cell therapy approach that could overcome the limitations of the current available treatments. In the present study we produced alginate-poly-L-lysine-alginate (APA) microcapsules containing recombinant cells overexpressing IDUA, which were implanted in the subcutaneous space of MPS I mice in order to evaluate their potential effect as a treatment for this disease. APA microcapsules enclosing genetically modified Baby Hamster Kidney cells overexpressing IDUA were produced and implanted in the subcutaneous space of 4-month-old MPS I mice (Idua -/-). Treatment was performed using two cell concentrations: 8.3 × 107 and 8.3 × 106 cells/mL. Untreated MPS I and normal mice were used as controls. Microcapsules were retrieved and analyzed after treatment. Increased IDUA in the liver, kidney and heart was detected 24 h postimplantation. After 120 days, higher IDUA activity was detected in the liver, kidney and heart, in both groups, whereas GAG accumulation was reduced only in the high cell concentration group. Microcapsules analysis showed blood vessels around them, as well as inflammatory cells and a fibrotic layer. Microencapsulated cells were able to ameliorate some aspects of the disease, indicating their potential as a treatment. To achieve better performance of the microcapsules, improvements such as the modulation of inflammatory response are suggested.

Identification and characterization of 20 novel pathogenic variants in 60 unrelated Indian patients with mucopolysaccharidoses type I and type II.

Mucopolysaccharidoses (MPS), a subgroup of lysosomal storage disorders, are caused due to deficiency of specific lysosomal enzyme involved in catabolism of glycosaminoglycans. To date more than 200 pathogenic variants in the alpha-l-iduronidase (IDUA) for MPS I and ∼500 pathogenic variants in the iduronate-2-sulphatase (IDS) for MPS II have been reported worldwide. The mutation spectrum of MPS type I and MPS type II disorders in Indian population is not characterized yet. In this study, we carried out clinical, biochemical, molecular and in silico analyses to establish the mutation spectrum of MPS I and MPS II in the Indian population. We conducted molecular analysis for 60 MPS-affected patients [MPS I (n = 30) (Hurler syndrome = 17, Hurler-Scheie syndrome = 13), and MPS II (n = 30) (severe = 18, attenuated = 12)] and identified a total of 44 [MPS I (n = 22) and MPS II (n = 22)] different pathogenic variants comprising missense, nonsense, frameshift, gross deletions and splice site variants. A total of 20 [MPS I (n = 14), and MPS II (n = 6)] novel pathogenic sequence variants were identified in our patient cohort. We found that 32% of pathogenic variants detected in IDUA were recurrent and 25% in MPS II. This is the first study revealing the mutation spectrum of MPS I and MPS II patients in the Indian population.

A method for measuring disease-specific iduronic acid from the non-reducing end of glycosaminoglycan in mucopolysaccharidosis type II mice.

Mucopolysaccharidosis type II (MPS II) is an X-linked lysosomal storage disorder arising from deficiency of iduronate-2-sulfatase (IDS), which results in progressive accumulation of glycosaminoglycans (GAGs) in multiple tissues. Accumulated GAGs are generally measured as the amount of total GAGs. However, we recently demonstrated that GAG accumulation in the brain of MPS II model mice cannot be reliably detected by conventional dye-binding assay measuring total GAGs. Here we developed a novel quantitative method for measurement of disease-specific GAGs based on the analysis of 2-sulfoiduronic acid levels derived from the non-reducing terminal end of the polysaccharides by using recombinant human IDS (rhIDS) and recombinant human iduronidase (rhIDUA). This method was evaluated on GAGs obtained from the liver and brain of MPS II mice. The GAGs were purified from tissue homogenates and then digested with rhIDS and rhIDUA to generate a desulfated iduronic acid from their non-reducing terminal end. HPLC analysis revealed that the generated iduronic acid levels were markedly increased in the liver and cerebrum of the MPS II mice, whereas the uronic acid was not detected in wild-type mice. These results indicate that this assay clearly detects the disease-specific GAGs in tissues from MPS II mice.

PEGylated cationic nanoemulsions can efficiently bind and transfect pIDUA in a mucopolysaccharidosis type I murine model.

Mucopolysaccharidosis type I (MPS I) is an autosomal disease caused by alpha-L-iduronidase deficiency. This study proposed the use of cationic nanoemulsions as non-viral vectors for a plasmid (pIDUA) containing the gene that codes for alpha-L-iduronidase. Nanoemulsions composed of medium chain triglycerides (MCT)/1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE)/1,2-dioleoyl-sn-glycero-3-trimethylammonium propane (DOTAP)/1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000] (DSPE-PEG) were prepared by high pressure homogenization. Formulations were prepared by the adsorption or encapsulation of preformed pIDUA-DOTAP complexes into the oil core of nanoemulsions at different charge ratios. pIDUA complexed was protected from enzymatic degradation by DNase I. The physicochemical characteristics of complexes in protein-containing medium were mainly influenced by the presence of DSPE-PEG. Bragg reflections corresponding to a lamellar organization were identified for blank formulations by energy dispersive X-ray diffraction, which could not be detected after pIDUA complexation. The intravenous injection of these formulations in MPS I knockout mice led to a significant increase in IDUA activity (fluorescence assay) and expression (RT-qPCR) in different organs, especially the lungs and liver. These findings were more significant for formulations prepared at higher charge ratios (+4/-), suggesting a correlation between charge ratio and transfection efficiency. The present preclinical results demonstrated that these nanocomplexes represent a potential therapeutic option for the treatment of MPS I.

Laronidase-functionalized multiple-wall lipid-core nanocapsules: promising formulation for a more effective treatment of mucopolysaccharidosis type I.

PURPOSE: Mucopolysaccharidosis I is a genetic disorder caused by alpha-L-iduronidase deficiency. Its primary treatment is enzyme replacement therapy (ERT), which has limitations such as a high cost and a need for repeated infusions over the patient's lifetime. Considering that nanotechnological approaches may enhance enzyme delivery to organs and can reduce the dosage thereby enhancing ERT efficiency and/or reducing its cost, we synthesized laronidase surface-functionalized lipid-core nanocapsules (L-MLNC). METHODS: L-MLNCs were synthesized by using a metal complex. Size distributions were evaluated by laser diffraction and dynamic light scattering. The kinetic properties, cytotoxicity, cell uptake mechanisms, clearance profile and biodistribution were evaluated. RESULTS: Size distributions showed a D[4,3] of 134 nm and a z-average diameter of 71 nm. L-MLNC enhanced the Vmax and Kcat in comparison with laronidase. L-MLNC is not cytotoxic, and nanocapsule uptake by active transport is not only mediated by mannose-6-phosphate receptors. The clearance profile is better for L-MLNC than for laronidase. A biodistribution analysis showed enhanced enzyme activity in different organs within 4 h and 24 h for L-MLNC. CONCLUSIONS: The use of lipid-core nanocapsules as building blocks to synthesize surface-functionalized nanocapsules represents a new platform for producing decorated soft nanoparticles that are able to modify drug biodistribution.

Lessons from molecular modeling human α-L-iduronidase.

Human α-L-iduronidase (IDUA) is a member of glycoside hydrolase family and is involved in the catabolism of glycosaminoglycans (GAGs), heparan sulfate (HS) and dermatan sulfate (DS). Mutations in this enzyme are responsible for mucopolysaccharidosis I (MPS I), an inherited lysosomal storage disorder. Despite great interest in determining and studying this enzyme structure, the lack of a high identity to templates and other technical issues have challenged both bioinformaticians and crystallographers, until the recent publication of an IDUA crystal structure (PDB: 4JXP). In the present work, four alternative IDUA models, generated and evaluated prior to crystallographic determination, were compared to the 4JXP structure. A combined analysis using several viability assessment tools and molecular dynamics simulations highlights the strengths and limitations of different comparative modeling protocols, all of which are based on the same low identity template (only 22%). Incorrect alignment between the target and template was confirmed to be a major bottleneck in homology modeling, regardless of the modeling software used. Moreover, secondary structure analysis during a 50ns simulation seems to be useful for indicating alignment errors and structural instabilities. The best model was achieved through the combined use of Phyre 2 and Modeller, suggesting the use of this protocol for the modeling of other proteins that still lack high identity templates.

Structural and clinical implications of amino acid substitutions in α-L-iduronidase: insight into the basis of mucopolysaccharidosis type I.

Allelic mutations, predominantly missense ones, of the α-l-iduronidase (IDUA) gene cause mucopolysaccharidosis type I (MPS I), which exhibits heterogeneous phenotypes. These phenotypes are basically classified into severe, intermediate, and attenuated types. We previously examined the structural changes in IDUA due to MPS I by homology modeling, but the reliability was limited because of the low sequence identity. In this study, we built new structural models of mutant IDUAs due to 57 amino acid substitutions that had been identified in 27 severe, 1 severe-intermediate, 13 intermediate, 1 attenuated-intermediate and 15 attenuated type MPS I patients based on the crystal structure of human IDUA, which was recently determined by us. The structural changes were examined by calculating the root-mean-square distances (RMSD) and the number of atoms influenced by the amino acid replacements. The results revealed that the structural changes of the enzyme protein tended to be correlated with the severity of the disease. Then we focused on the structural changes resulting from amino acid replacements in the immunoglobulin-like domain and adjacent region, of which the structure had been missing in the IDUA model previously built. Coloring of atoms influenced by an amino acid substitution was performed in each case and the results revealed that the structural changes occurred in a region far from the active site of IDUA, suggesting that they affected protein folding. Structural analysis is thus useful for elucidation of the basis of MPS I.

Identification of mucopolysaccharidosis I heterozygotes based on biochemical characteristics of L-iduronidase from dried blood spots.

BACKGROUND: Mucopolysaccharidosis I (MPS I) is a genetic disorder caused by deficiency of L-iduronidase (IDUA) activity. Heterozygote screening is a highly requested service by risk families; however, determination of IDUA activity alone is not sufficient to discriminate between heterozygotes and normal individuals because a significant overlap occurs between them. The aim of this study was to characterize the enzyme eluted from heterozygote's dried blood samples and determine if there are differences with that of normal individuals. METHODS: We determined Km, Vmax and the thermal stability of the enzyme at 50 °C. RESULTS: Vmax from heterozygotes (7.28 ± 2.72 µmol/l blood/h) was significantly different than the obtained in controls (10.52 ± 2.05 µmol/l blood/h), while their Km were similar: 0.633 ± 0.339 mmol/l and 0.672 ± 0.246 mmol/l, respectively. After a 12 h pre-incubation period, IDUA activity in controls was significantly lower compared to heterozygotes. CONCLUSIONS: IDUA eluted from dried blood spots of heterozygotes differs from that of controls in terms of Vmax and thermal stability. These parameters can be used as an important tool for the detection of carriers for MPS I. This is the first report describing a differential behavior of these parameters for a lysosomal enzyme obtained from dried blood.

Insights into mucopolysaccharidosis I from the structure and action of α-L-iduronidase.

Mucopolysaccharidosis type I (MPS I), caused by mutations in the gene encoding α-L-iduronidase (IDUA), is one of approximately 70 genetic disorders collectively known as the lysosomal storage diseases. To gain insight into the basis for MPS I, we crystallized human IDUA produced in an Arabidopsis thaliana cgl mutant. IDUA consists of a TIM barrel domain containing the catalytic site, a ß-sandwich domain and a fibronectin-like domain. Structures of IDUA bound to iduronate analogs illustrate the Michaelis complex and reveal a (2,5)B conformation in the glycosyl-enzyme intermediate, which suggest a retaining double displacement reaction involving the nucleophilic Glu299 and the general acid/base Glu182. Unexpectedly, the N-glycan attached to Asn372 interacts with iduronate analogs in the active site and is required for enzymatic activity. Finally, these IDUA structures and biochemical analysis of the disease-relevant P533R mutation have enabled us to correlate the effects of mutations in IDUA to clinical phenotypes.

Human α-L-iduronidase uses its own N-glycan as a substrate-binding and catalytic module.

N-glycosylation is a major posttranslational modification that endows proteins with various functions. It is established that N-glycans are essential for the correct folding and stability of some enzymes; however, the actual effects of N-glycans on their activities are poorly understood. Here, we show that human α-l-iduronidase (hIDUA), of which a dysfunction causes accumulation of dermatan/heparan sulfate leading to mucopolysaccharidosis type I, uses its own N-glycan as a substrate binding and catalytic module. Structural analysis revealed that the mannose residue of the N-glycan attached to N372 constituted a part of the substrate-binding pocket and interacted directly with a substrate. A deglycosylation study showed that enzyme activity was highly correlated with the N-glycan attached to N372. The kinetics of native and deglycosylated hIDUA suggested that the N-glycan is also involved in catalytic processes. Our study demonstrates a previously unrecognized function of N-glycans.

Characterization and downstream mannose phosphorylation of human recombinant α-L-iduronidase produced in Arabidopsis complex glycan-deficient (cgl) seeds.

Mucopolysaccharidosis (MPS) I is a lysosomal storage disease caused by a deficiency of α-L-iduronidase (IDUA) (EC 3.2.1.76); enzyme replacement therapy is the conventional treatment for this genetic disease. Arabidopsis cgl mutants are characterized by a deficiency of the activity of N-acetylglucosaminyl transferase I (EC 2.4.1.101), the first enzyme in the pathway of hybrid and complex N-glycan biosynthesis. To develop a seed-based platform for the production of recombinant IDUA for potential treatment of MPS I, cgl mutant seeds were generated to express human IDUA at high yields and to avoid maturation of the N-linked glycans on the recombinant human enzyme. Enzyme kinetic data showed that cgl-IDUA has similar enzymatic properties to the commercial recombinant IDUA derived from cultured Chinese hamster ovary (CHO) cells (Aldurazyme™). The N-glycan profile showed that cgl-derived IDUA contained predominantly high-mannose-type N-glycans (94.5%), and the residual complex/hybrid N-glycan-containing enzyme was efficiently removed by an additional affinity chromatography step. Furthermore, purified cgl-IDUA was amenable to sequential in vitro processing by soluble recombinant forms of the two enzymes that mediate the addition of the mannose-6-phosphate (M6P) tag in mammalian cells-UDP-GlcNAc:lysosomal enzyme N-acetylglucosamine (GlcNAc)-1-phosphotransferase-and GlcNAc-1-phosphodiester α-N-acetylglucosaminidase (the 'uncovering enzyme'). Arabidopsis seeds provide an alternative system for producing recombinant lysosomal enzymes for enzyme replacement therapy; the purified enzymes can be subjected to downstream processing to create the M6P, a recognition marker essential for efficient receptor-mediated uptake into lysosomes of human cells.

Screening of lysosomal storage disorders: application of the online trapping-and-cleanup liquid chromatography/mass spectrometry method for mucopolysaccharidosis I.

In recent years, new treatments have become available to treat some lysosomal storage disorders (LSDs) and many studies suggest that there is a benefit with starting therapy early. Newborn screening should detect diseases early enough for prompt treatment. Some countries include additional conditions, such as some LSDs, into their newborn screening panels. Mucopolysaccharidosis Type I (MPS I) is an autosomal recessive disorder caused by the deficiency of α-L-iduronidase (IDUA) activity. Currently, enzyme replacement therapy (ERT) or bone marrow transplantation is available and this has raised a growing interest for the development of a newborn screening test. In 2009, we reported a new fast and simplified tandem mass spectrometry-based method for quantifying five enzyme activities on dried blood spots. Here, we describe the inclusion of IDUA activity determination for the simultaneous detection of six lysosomal storage diseases. We have defined reference normal ranges by testing 680 healthy newborns and 240 adults. The assay was checked through three confirmed MPS I patients whose IDUA activity was below the normal range. Reproducibility of the assays has been established by assessing the intra-day and inter-day assay imprecisions. This quick assay has been devised to be implemented in newborn screening by liquid chromatography tandem mass spectrometry.

Characterization of α-l-Iduronidase (Aldurazyme®) and its complexes.

Alpha-l-Iduronidase(IDUA) was the first enzyme replacement therapy approved for mucopolysaccharidosis type I and the corresponding recombinant protein drug, Aldurazyme®, is commercially available. In the frame of gel-based mass spectrometrical characterization of protein drugs, we intended to identify protein sequence and possible protein modifications. Moreover, we were interested in which aggregation/complex form Aldurazyme® would exist, which complexes were enzymatically active and in which form the naturally occurring enzyme would be present in the brain. Aldurazyme® was run on 2DE gel electrophoresis, spots were excised, in-gel digested with several proteases and identified by nano-LC-ESI-MS/MS on an ion trap. IDUA-activity was determined by a fluorometric principle. Blue-native gel electrophoresis with subsequent immunoblotting was carried out to show the presence of protein complexes. The protein was unambiguously identified by 100% sequence coverage; several amino acid substitutions were detected and protein modifications were novel phosphorylations on S59 and S482, histidine methylation at H572 and provide evidence for already known N-glycosylations. Four Aldurazyme® complexes that all were enzymatically active, were observed while a single complex was observed for the physiologically occurring IDUA in the brain. The findings are relevant for understanding chemistry, physiology, pharmacology and medicine of IDUA, design of further and interpretation of previous work.

Crystallization, X-ray diffraction analysis and SIRAS phasing of human α-L-iduronidase.

Human lysosomal α-L-iduronidase, whose deficiency causes mucopolysaccharidosis type I, was crystallized using sodium/potassium tartrate and polyethylene glycol 3350 as a precipitant. Using synchrotron radiation, a native data set was collected from a single crystal at 100 K to 2.3 Šresolution. The crystal belonged to space group R3 with unit-cell dimensions of a=b=259.22, c=71.83 Å. To obtain the phase information, mercury-derivative crystals were prepared and a single-wavelength anomalous dispersion (SAD) data set was collected at the Hg peak wavelength. Phase calculation with the single isomorphous replacement with anomalous scattering (SIRAS) method successfully yielded an interpretable electron-density map.