Identification of Orthosteric and Allosteric Pharmacological Chaperones for Mucopolysaccharidosis Type IIIB.

Mucopolysaccharidosis type IIIB (MPS IIIB) is an autosomal inherited disease caused by mutations in gene encoding the lysosomal enzyme N-acetyl-alpha-glucosaminidase (NAGLU). These mutations result in reduced NAGLU activity, preventing it from catalyzing the hydrolysis of the glycosaminoglycan heparan sulfate (HS). There are currently no approved treatments for MPS IIIB. A novel approach in the treatment of lysosomal storage diseases is the use of pharmacological chaperones (PC). In this study, we used a drug repurposing approach to identify and characterize novel potential PCs for NAGLU enzyme. We modeled the interaction of natural and artificial substrates within the active cavity of NAGLU (orthosteric site) and predicted potential allosteric sites. We performed a virtual screening for both the orthosteric and the predicted allosteric site against a curated database of human tested molecules. Considering the binding affinity and predicted blood-brain barrier permeability and gastrointestinal absorption, we selected atovaquone and piperaquine as orthosteric and allosteric PCs. The PCs were evaluated by their capacity to bind NAGLU and the ability to restore the enzymatic activity in human MPS IIIB fibroblasts These results represent novel PCs described for MPS IIIB and demonstrate the potential to develop novel therapeutic alternatives for this and other protein deficiency diseases.

Polymorphic variants (p.Ser141Ser and p.Arg737Gly) at the NAGLU gene are really indicative of pseudodeficiency alleles?

Filocamo et al. recently published a paper describing the presence of a pseudodeficiency allele, constituted by p.Ser141Ser and p.Arg737Gly polymorphisms at the NAGLU gene, which leads to a reduced level of the alpha-N-acetyl-D-glucosaminidase activity. Based on analysis performed in Brazilian patients, using a customized gene panel containing SGSH, NAGLU, HGSNAT and GNS we observed that p.Ser141Ser (rs659497) and p.Arg737Gly (rs86312) variants were present in homozygosis in all of our MPS IIIB patients and in the majority of MPS IIIA, IIIC and IIID patients, and there was no significant decrease of the alpha-N-acetyl-D-glucosaminidase enzyme activity in this group when compared with those without the "pseudodeficiency allele". Thus, we suggest that these two variants are not producing a pseudodeficiency allele.

Cloning and Characterization of a Novel N-acetylglucosaminidase (AtlD) from Enterococcus faecalis.

The atlD gene from an Enterococcus faecalis strain isolated from a Mexican artisanal cheese was cloned, sequenced and expressed in Escherichia coli in order to perform a biochemical characterization. A partial amino acid sequence of the heterologous protein was obtained by LC-MS/MS, and it corresponded to a novel peptidoglycan hydrolase designated AtlD. Its molecular mass was 62-75 kDa, as determined by SDS-PAGE, zymography, Western blot, and exclusion chromatography. Electrofocusing rendered an isoelectric point (pI) of 4.8. It exhibited N-acetylglucosaminidase activity, with an optimal pH and temperature between 6-7 and 50°C, respectively. It retained 85% activity with NaCl at 1,000 mM, but it was susceptible to divalent ions, particularly Zn2+. It showed antibacterial activity against Listeria monocytogenes, Staphylococcus aureus, and enterococcal strains of clinical origin. Due to the fact that it showed activity versus pathogenic bacteria, and because of its capabilities under ionic strength, temperature, and pH values present in food matrices, it could be applied as an additive in the food industry. This study will aid in the design of new antibacterial agents of natural origin to combat food-borne diseases, and it could be used as an industrial or hospital hygiene agent as well.

Molecular defects identified by whole exome sequencing in a child with atypical mucopolysaccharidosis IIIB.

BACKGROUND: Mucopolysaccharidosis IIIB (MPS IIIB) is a genetic disease characterized by mutations in the NAGLU gene, deficiency of α-N-acetylglucosaminidase, multiple congenital malformations and an increased susceptibility to malignancy. Because of the slow progressive nature of this disease and its atypical symptoms, the misdiagnosis of MPS IIIB is not rare in clinical practice. This misdiagnosis could be avoided by using next-generation sequencing (NGS) techniques, which have been shown to have superior performance for detecting mutations underlying rare inherited disorders in previous studies. CASE PRESENTATION: Whole exome sequencing (WES) was conducted and the putative pathogenic variants were validated by Sanger sequencing. The activity of MPS IIIB related enzyme in the patient's blood serum was assayed. A heterozygous, non-synonymous mutation (c.1562C>T, p.P521L) as well as a novel mutation (c.1705C>A, p.Q569K) were found in the NAGLU gene of the patient. The two mutations were validated by Sanger sequencing. Our data showed that this patient's c.1562C>T, p.P521L mutation in the NAGLU gene was inherited from his father and c.1705C>A, p.Q569K was from his mother. The diagnosis was further confirmed by an enzymatic activity assay after patient recall and follow-up. CONCLUSIONS: Our results describe an atypical form of MPS IIIB and illustrate the diagnostic potential of targeted WES in Mendelian disease with unknown etiology. WES could become a powerful tool for molecular diagnosis of MPS IIIB in clinical setting.

On the phosphorylase activity of GH3 enzymes: A ß-N-acetylglucosaminidase from Herbaspirillum seropedicae SmR1 and a glucosidase from Saccharopolyspora erythraea.

A phosphorolytic activity has been reported for beta-N-acetylglucosaminidases from glycoside hydrolase family 3 (GH3) giving an interesting explanation for an unusual histidine as catalytic acid/base residue and suggesting that members from this family may be phosphorylases [J. Biol. Chem. 2015, 290, 4887]. Here, we describe the characterization of Hsero1941, a GH3 beta-N-acetylglucosaminidase from the endophytic nitrogen-fixing bacterium Herbaspirillum seropedicae SmR1. The enzyme has significantly higher activity against pNP-beta-D-GlcNAcp (Km = 0.24 mM, kcat = 1.2 s-1, kcat/Km = 5.0 mM-1s-1) than pNP-beta-D-Glcp (Km = 33 mM, kcat = 3.3 × 10-3 s-1, kcat/Km = 9 × 10-4 mM-1s-1). The presence of phosphate failed to significantly modify the kinetic parameters of the reaction. The enzyme showed a broad aglycone site specificity, being able to hydrolyze sugar phosphates beta-D-GlcNAc 1P and beta-D-Glc 1P, albeit at a fraction of the rate of hydrolysis of aryl glycosides. GH3 beta-glucosidase EryBI, that does not have a histidine as the general acid/base residue, also hydrolyzed beta-D-Glc 1P, at comparable rates to Hsero1941. These data indicate that Hsero1941 functions primarily as a hydrolase and that phosphorolytic activity is likely adventitious. The prevalence of histidine as a general acid/base residue is not predictive, nor correlative, with GH3 beta-N-acetylglucosaminidases having phosphorolytic activity.

Role for high-glucose-induced protein O-GlcNAcylation in stimulating cardiac fibroblast collagen synthesis.

Excess enzyme-mediated protein O-GlcNAcylation is known to occur with diabetes mellitus. A characteristic of diabetic cardiomyopathy is the development of myocardial fibrosis. The role that enhanced protein O-GlcNAcylation plays in modulating the phenotype of cardiac fibroblasts (CF) is unknown. To address this issue, rat CF were cultured in normal glucose (NG; 5 mM glucose) or high-glucose (HG; 25 mM) media for 48 h. Results demonstrate that CF cultured in HG have higher levels (~50%) of overall protein O-GlcNAcylation vs. NG cells. Key regulators of collagen synthesis such as transforming-growth factor-ß1 (TGF-ß1), SMADs 2/3, and SMAD 7 protein levels, including those of arginase I and II, were altered, leading to increases in collagen levels. The nuclear transcription factor Sp1 and arginase II evidence excess O-GlcNAcylation in HG cells. Expression in CF of an adenovirus coding for the enzyme N-acetylglucosaminidase, which removes O-GlcNAc moieties from proteins, decreased Sp1 and arginase II O-GlcNAcylation and restored HG-induced perturbations in CF back to NG levels. These findings may have important pathophysiological implications for the development of diabetes-induced cardiac fibrosis.

Potentiation of the synergistic activities of chitinases ChiA, ChiB and ChiC from Serratia marcescens CFFSUR-B2 by chitobiase (Chb) and chitin binding protein (CBP).

With the goal of understanding the chitinolytic mechanism of the potential biological control strain Serratia marcescens CFFSUR-B2, genes encoding chitinases ChiA, ChiB and ChiC, chitobiase (Chb) and chitin binding protein (CBP) were cloned, the protein products overexpressed in Escherichia coli as 6His-Sumo fusion proteins and purified by affinity chromatography. Following affinity tag removal, the chitinolytic activity of the recombinant proteins was evaluated individually and in combination using colloidal chitin as substrate. ChiB and ChiC were highly active while ChiA was inactive. Reactions containing both ChiB and ChiC showed significantly increased N-acetylglucosamine trimer and dimer formation, but decreased monomer formation, compared to reactions with either enzyme alone. This suggests that while both ChiB and ChiC have a general affinity for the same substrate, they attack different sites and together degrade chitin more efficiently than either enzyme separately. Chb and CBP in combination with ChiB and ChiC (individually or together) increased their chitinase activity. We report for the first time the potentiating effect of Chb on the activity of the chitinases and the synergistic activity of a mixture of all five proteins (the three chitinases, Chb and CBP). These results contribute to our understanding of the mechanism of action of the chitinases produced by strain CFFSUR-B2 and provide a molecular basis for its high potential as a biocontrol agent against fungal pathogens.

RNA interference of endochitinases in the sugarcane endophyte Trichoderma virens 223 reduces its fitness as a biocontrol agent of pineapple disease.

The sugarcane root endophyte Trichoderma virens 223 holds enormous potential as a sustainable alternative to chemical pesticides in the control of sugarcane diseases. Its efficacy as a biocontrol agent is thought to be associated with its production of chitinase enzymes, including N-acetyl-ß-D-glucosaminidases, chitobiosidases and endochitinases. We used targeted gene deletion and RNA-dependent gene silencing strategies to disrupt N-acetyl-ß-D-glucosaminidase and endochitinase activities of the fungus, and to determine their roles in the biocontrol of soil-borne plant pathogens. The loss of N-acetyl-ß-D-glucosaminidase activities was dispensable for biocontrol of the plurivorous damping-off pathogens Rhizoctonia solani and Sclerotinia sclerotiorum, and of the sugarcane pathogen Ceratocystis paradoxa, the causal agent of pineapple disease. Similarly, suppression of endochitinase activities had no effect on R. solani and S. sclerotiorum disease control, but had a pronounced effect on the ability of T. virens 223 to control pineapple disease. Our work demonstrates a critical requirement for T. virens 223 endochitinase activity in the biocontrol of C. paradoxa sugarcane disease, but not for general antagonism of other soil pathogens. This may reflect its lifestyle as a sugarcane root endophyte.

ß-hexosaminidase from Xenopus laevis eggs and oocytes: from gene to immunochemical characterization.

Glycosidases are present both in sperm and eggs in vertebrates and have been associated with different fertilization steps as gamete binding, egg coat penetration, and polyspermy prevention. In this manuscript, we have analyzed the activity of different glycosidases of Xenopus laevis eggs. The main activity corresponded to N-acetyl-ß-D-glucosaminidase (Hex), which was reported to participate both in gamete binding and polyspermy prevention among phylogenetically distant animals. We have raised homologous antibodies against a recombinant N-terminal fragment of a X. laevis Hex, and characterized egg's Hex both by Western blot and immunohistochemical assays. Noteworthy, Hex was mainly localized to the cortex of animal hemisphere of full-grown oocytes and oviposited eggs, and remained unaltered after fertilization. Hex is constituted by different pair arrangements of two subunits (α and ß), giving rise to three possible Hex isoforms: A (αß), B (ßß), and S (αα). However, no information was available regarding molecular identity of Hex in amphibians. We present for the first time the primary sequences of two isoforms of X. laevis Hex. Interestingly, our results suggest that α- and ß-like subunits that constitute Hex isoforms could be synthesized from a same gene in Xenopus, by alternative exon use. This finding denotes an evolutionary divergence with mammals, where α and ß Hex subunits are synthesized from different genes on different chromosomes.

A single nucleotide polymorphism in MGEA5 encoding O-GlcNAc-selective N-acetyl-beta-D glucosaminidase is associated with type 2 diabetes in Mexican Americans.

Excess O-glycosylation of proteins by O-linked beta-N-acetylglucosamine (O-GlcNAc) may be involved in the pathogenesis of type 2 diabetes. The enzyme O-GlcNAc-selective N-acetyl-beta-d glucosaminidase (O-GlcNAcase) encoded by MGEA5 on 10q24.1-q24.3 reverses this modification by catalyzing the removal of O-GlcNAc. We have previously reported the linkage of type 2 diabetes and age at diabetes onset to an overlapping region on chromosome 10q in the San Antonio Family Diabetes Study (SAFADS). In this study, we investigated menangioma-expressed antigen-5 (MGEA5) as a positional candidate gene. Twenty-four single nucleotide polymorphisms (SNPs), identified by sequencing 44 SAFADS subjects, were genotyped in 436 individuals from 27 families whose data were used in the original linkage report. Association tests indicated significant association of a novel SNP with the traits diabetes (P = 0.0128, relative risk = 2.77) and age at diabetes onset (P = 0.0017). The associated SNP is located in intron 10, which contains an alternate stop codon and may lead to decreased expression of the 130-kDa isoform, the isoform predicted to contain the O-GlcNAcase activity. We investigated whether this variant was responsible for the original linkage signal. The variance attributed to this SNP accounted for approximately 25% of the logarithm of odds. These results suggest that this variant within the MGEA5 gene may increase diabetes risk in Mexican Americans.

Regulation of N-acetyl-beta-D-glucosaminidase produced by Trichoderma harzianum: evidence that cAMP controls its expression.

Trichoderma harzianum is a filamentous fungus reported to be a producer of extracellular N-acetyl-beta-D-glucosaminidase (NAGase) when grown in chitin-containing medium. An approximately 64-kDa protein with NAGase activity was purified by gel filtration and ion exchange chromatography. The involvement of cyclic AMP (cAMP) in the synthesis of NAGase from T. harzianum in chitin-containing medium was also investigated. Molecules that increase the intracellular levels of cAMP, including caffeine, aluminium tetrafluoride and dinitrophenol, were used. Western blot analysis showed that NAGase synthesis was repressed by increasing the levels of intracellular cAMP. Using specific nag primers in a reverse transcription-polymerase chain reaction-based approach, NAGase synthesis was shown to be regulated at the level of gene transcription.

Molecular cloning and characterization of a cDNA encoding the N-acetyl-beta-D-glucosaminidase homologue of Paracoccidioides brasiliensis.

A cDNA encoding the N-acetyl-beta-D-glucosaminidase (NAG) protein of Paracoccidioides brasiliensis, Pb NAG1, was cloned and characterized. The 2663-nucleotide sequence of the cDNA consisted of a single open reading frame encoding a protein with a predicted molecular mass of 64.73 kDa and an isoeletric point of 6.35. The predicted protein includes a putative 30-amino-acid signal peptide. The protein as a whole shares considerable sequence similarity with 'classic' NAG. The primary sequence of Pb NAG1 was used to infer phylogenetic relationships. The amino acid sequence of Pb NAG1 has 45, 31 and 30% identity, respectively, with homologous sequences from Trichoderma harzianum, Aspergillus nidulans and Candida albicans. In particular, striking homology was observed with the active site regions of the glycosyl hydrolase group of proteins (family 20). The expected active site consensus motif G X D E and catalytic Asp and Glu residues at positions 373 and 374 were found, reinforcing that Pb NAG1 belongs to glycosyl hydrolase family 20. The nucleotide sequence of Pb nag1 and its flanking regions have been deposited, along with the amino acid sequence of the deduced protein, in GenBank under accession number AF419158.

Enhanced glomerular permeability to macromolecules in the Nagase analbuminemic rat.

Plasma albumin restricts capillary water filtration. Accordingly, the glomerular ultrafiltration coefficient is higher in Nagase analbuminemic rats (NAR) than in Sprague-Dawley controls. We investigated whether the glomerular permeability to macromolecules is also enhanced in NAR. SDS-PAGE fractionation of urine proteins showed several bands with molecular masses between 60 and 90 kDa in NAR only. Acute administration of BSA to NAR led to nearly complete disappearance of these proteins from urine, an effect partially reversed when most of the exogenous albumin was cleared from circulation. The fractional clearance of 70-kDa dextran was increased in NAR, indicating a size defect. Binding of cationized ferritin to the glomerular basement membrane was decreased in NAR, suggesting associated depletion of fixed anions. The magnitude of cationic ferritin binding correlated negatively with the fractional clearance of 70-kDa dextran, suggesting that the two abnormalities may share a common pathogenic mechanism. Collectively, these results suggest enhanced glomerular permeability to macromolecules in NAR. Albumin may be necessary to maintain the normal glomerular permselectivity properties.