A chondroitin synthase-1 (ChSy-1) missense mutation in a patient with neuropathy impairs the elongation of chondroitin sulfate chains initiated by chondroitin N-acetylgalactosaminyltransferase-1

Background

Previously, we identified two missense mutations in the chondroitin N-acetylgalactosaminyltransferase-1 gene in patients with neuropathy. These mutations are associated with a profound decrease in chondroitin N-acetylgalactosaminyltransferase-1 enzyme activity. Here, we describe a patient with neuropathy who is heterozygous for a chondroitin synthase-1 mutation. Chondroitin synthase-1 has two glycosyltransferase activities: it acts as a GlcUA and a GalNAc transferase and is responsible for adding repeated disaccharide units to growing chondroitin sulfate chains.

Methods

Recombinant wild-type chondroitin synthase-1 enzyme and the F362S mutant were expressed. These enzymes and cells expressing them were then characterized.

Results

The mutant chondroitin synthase-1 protein retained approximately 50% of each glycosyltransferase activity relative to the wild-type chondroitin synthase-1 protein. Furthermore, unlike chondroitin polymerase comprised of wild-type chondroitin synthase-1 protein, the non-reducing terminal 4-O-sulfation of GalNAc residues synthesized by chondroitin N-acetylgalactosaminyltransferase-1 did not facilitate the elongation of chondroitin sulfate chains when chondroitin polymerase that consists of the mutant chondroitin synthase-1 protein was used as the enzyme source.

Conclusions

The chondroitin synthase-1 F362S mutation in a patient with neuropathy resulted in a decrease in chondroitin polymerization activity and the mutant protein was defective in regulating the number of chondroitin sulfate chains via chondroitin N-acetylgalactosaminyltransferase-1. Thus, the progression of peripheral neuropathies may result from defects in these regulatory systems.

General significance

The elongation of chondroitin sulfate chains may be tightly regulated by the cooperative expression of chondroitin synthase-1 and chondroitin N-acetylgalactosaminyltransferase-1 in peripheral neurons and peripheral neuropathies may result from synthesis of abnormally truncated chondroitin sulfate chains.     

Substrate-mediated proton relay mechanism for the religation reaction in topoisomerase II

The DNA religation reaction of yeast type II topoisomerase (topo II) was investigated to elucidate its metal-dependent general acid/base catalysis. Quantum mechanical/molecular mechanical calculations were performed for the topo II religation reaction, and the proton transfer pathway was examined. We found a substrate-mediated proton transfer of the topo II religation reaction, which involves the 3′ OH nucleophile, the reactive phosphate, water, Arg781, and Tyr782. Metal A stabilizes the transition states, which is consistent with a two-metal mechanism in topo II. This pathway may be required for the cleavage/religation reaction of topo IA and II and will provide a general explanation for the catalytic mechanism in the topo IA and II.     

RNAi suppression of β-N-acetylglucosaminidase (BmFDL) for complex-type N-linked glycan synthesis in cultured silkworm cells

Glycoproteins have various biological functions including enzymatic activity, protein stability and others. Due to the presence of paucimannosidic N-linked glycans, recombinant proteins from an insect cell expression system may not be suitable for therapeutic use. Because baculovirus expression systems (BESs) are used to produce recombinant proteins, it is of interest to modify the endogenous N-glycosylation pathway in insects to mimic that of mammals. Using a soaking RNAi sensitive cell line, BmN4-SID1, has enabled us to suppress Bombyx mori FDL (BmFDL), an N-linked glycan-specific β-N-acetylglucosaminidase. Western blotting and MALDI-TOF MS demonstrated that the BmFDL depletion almost completely converted the paucimannosidic structures of the recombinant proteins produced by BES into a complex-type structure. This highly efficient, simple and low-cost method can be used for mass production of secretion proteins with complex-type N-linked glycans.     

Induction of Anti-influenza Immunity by Modified Green Fluorescent Protein (GFP) Carrying Hemagglutinin-derived Epitope Structure

The development of vaccination methods that can overcome the emergence of new types of influenza strains caused by escape mutations is desirable to avoid future pandemics. Here, a novel type of immunogen was designed that targeted the conformation of a highly conserved region of influenza A virus hemagglutinin (HA) composed of two separate sequences that associate to form an anti-parallel β-sheet structure. Our previous study identified this β-sheet region as the structural core in the epitope of a characteristic antibody (B-1) that strongly neutralizes a wide variety of strains within the H3N2 serotype, and therefore this β-sheet region was considered a good target to induce broadly reactive immunity against the influenza A virus. To design the immunogen, residues derived from the B-1 epitope were introduced directly onto a part of enhanced green fluorescent protein (EGFP), whose surface is mostly composed of β-sheets. Through site-directed mutagenesis, several modified EGFPs with an epitope-mimicking structure embedded in their surface were prepared. Two EGFP variants, differing from wild-type (parental) EGFP by only five and nine residues, induced mice to produce antibodies that specifically bind to H3-type HA and neutralize H3N2 virus. Moreover, three of five mice immunized with each of these EGFP variants followed by a booster with equivalent mCherry variants acquired anti-viral immunity against challenge with H3N2 virus at a lethal dosage. In contrast to conventional methods, such as split HA vaccine, preparation of this type of immunogen requires less time and is therefore expected to be quickly responsive to newly emerged influenza viral strains.     

An Exopolygalacturonase from a Strain of Acrocylindrium

An exopolygalacturonase was partially purified from mycelial extracts of a strain of Acrocylindrium. The enzyme was most active at pH 4.5 and showed a higher affinity for polygalac turo nic acid than for oligogalacturonic acids. The enzyme was found to hydrolyze glycosidic linkages at the non-reducing end of polygalacturonic acid molecules, giving only monogalacturonic acid as the reaction product.     

Studies on Respiratory Enzymes in Rice Kernel

Rice embryo peroxidase 556 was purified to the extent as indicated by the absorbance ratio, RZ greater than 4.0. The enzyme was found to be major basic component among isoenzymes of rice embryo. The preparation was homogeneous as examined by sedimentation analysis, and the sedimentation coefficient, s°_20,w, was 3.76 S. The prosthetic group of the enzyme was identified as protohematin and its content was 1.36%. The minimum molecular weight was calculated to be 46,700. From the typical spectra of ligand-enzyme compounds, peroxidase 556 was found to react with carbon monoxide, cyanide, fluoride, and azide. However, at neutral pH, neither fluoride nor azide reacted with the enzyme. The high affinity of the enzyme to ammonia was one of the most remarkable characteristics of the enzyme. The hydrogen peroxide compounds I and II have been observed in the enzymic reaction, and therefore rice embryo peroxidase 556 is also concluded to follow the common reaction mechanism of plant peroxidases. Overall results show the close resemblance of rice embryo peroxidase 556 with wheat germ peroxidase 556 and hemoprotein 550.     

Polylysine Produced by Streptomyces

The xylitol dehydrogenase gene (xdh) of Bacillus pallidus was cloned and overexpressed in Escherichia coli using pQE60 vector, for the first time. The open reading frame of 759 bp encoded a 253 amino acid protein with a calculated molecular mass of 27,333 Da. The recombinant xylitol dehydrogenase (XDH) was purified to homogeneity by three-step column chromatography, producing a single SDS–PAGE band of 28 kDa apparent molecular mass. The enzyme exhibited maximal activity at 55 °C in glycine-NaOH buffer pH 11.0, with 66% of initial enzyme activity retained after incubation at 40 °C for 1 h. In further application of the recombinant bacterium to L-xylulose production from xylitol (initial concentration 5%) using a resting cell reaction, 35% L-xylulose was produced within 24 h. This result indicates that this recombinant XDH is applicable in the large-scale production of L-xylulose.