Japanese Encephalitis Virus Core Protein Inhibits Stress Granule Formation through an Interaction with Caprin-1 and Facilitates Viral Propagation

Stress granules (SGs) are cytoplasmic foci composed of stalled translation preinitiation complexes induced by environmental stress stimuli, including viral infection. Since viral propagation completely depends on the host translational machinery, many viruses have evolved to circumvent the induction of SGs or co-opt SG components. In this study, we found that expression of Japanese encephalitis virus (JEV) core protein inhibits SG formation. Caprin-1 was identified as a binding partner of the core protein by an affinity capture mass spectrometry analysis. Alanine scanning mutagenesis revealed that Lys⁹⁷ and Arg⁹⁸ in the α-helix of the JEV core protein play a crucial role in the interaction with Caprin-1. In cells infected with a mutant JEV in which Lys⁹⁷ and Arg⁹⁸ were replaced with alanines in the core protein, the inhibition of SG formation was abrogated, and viral propagation was impaired. Furthermore, the mutant JEV exhibited attenuated virulence in mice. These results suggest that the JEV core protein circumvents translational shutoff by inhibiting SG formation through an interaction with Caprin-1 and facilitates viral propagation in vitro and in vivo.     

Discovery of β-1,4-d-Mannosyl-N-acetyl-d-glucosamine Phosphorylase Involved in the Metabolism of N-Glycans

A gene cluster involved in N-glycan metabolism was identified in the genome of Bacteroides thetaiotaomicron VPI-5482. This gene cluster encodes a major facilitator superfamily transporter, a starch utilization system-like transporter consisting of a TonB-dependent oligosaccharide transporter and an outer membrane lipoprotein, four glycoside hydrolases (α-mannosidase, β-N-acetylhexosaminidase, exo-α-sialidase, and endo-β-N-acetylglucosaminidase), and a phosphorylase (BT1033) with unknown function. It was demonstrated that BT1033 catalyzed the reversible phosphorolysis of β-1,4-d-mannosyl-N-acetyl-d-glucosamine in a typical sequential Bi Bi mechanism. These results indicate that BT1033 plays a crucial role as a key enzyme in the N-glycan catabolism where β-1,4-d-mannosyl-N-acetyl-d-glucosamine is liberated from N-glycans by sequential glycoside hydrolase-catalyzed reactions, transported into the cell, and intracellularly converted into α-d-mannose 1-phosphate and N-acetyl-d-glucosamine. In addition, intestinal anaerobic bacteria such as Bacteroides fragilis, Bacteroides helcogenes, Bacteroides salanitronis, Bacteroides vulgatus, Prevotella denticola, Prevotella dentalis, Prevotella melaninogenica, Parabacteroides distasonis, and Alistipes finegoldii were also suggested to possess the similar metabolic pathway for N-glycans. A notable feature of the new metabolic pathway for N-glycans is the more efficient use of ATP-stored energy, in comparison with the conventional pathway where β-mannosidase and ATP-dependent hexokinase participate, because it is possible to directly phosphorylate the d-mannose residue of β-1,4-d-mannosyl-N-acetyl-d-glucosamine to enter glycolysis. This is the first report of a metabolic pathway for N-glycans that includes a phosphorylase. We propose 4-O-β-d-mannopyranosyl-N-acetyl-d-glucosamine:phosphate α-d-mannosyltransferase as the systematic name and β-1,4-d-mannosyl-N-acetyl-d-glucosamine phosphorylase as the short name for BT1033.     

Aberrant Assembly of RNA Recognition Motif 1 Links to Pathogenic Conversion of TAR DNA-binding Protein of 43 kDa (TDP-43)

Aggregation of TAR DNA-binding protein of 43 kDa (TDP-43) is a pathological signature of amyotrophic lateral sclerosis (ALS). Although accumulating evidence suggests the involvement of RNA recognition motifs (RRMs) in TDP-43 proteinopathy, it remains unclear how native TDP-43 is converted to pathogenic forms. To elucidate the role of homeostasis of RRM1 structure in ALS pathogenesis, conformations of RRM1 under high pressure were monitored by NMR. We first found that RRM1 was prone to aggregation and had three regions showing stable chemical shifts during misfolding. Moreover, mass spectrometric analysis of aggregated RRM1 revealed that one of the regions was located on protease-resistant β-strands containing two cysteines (Cys-173 and Cys-175), indicating that this region served as a core assembly interface in RRM1 aggregation. Although a fraction of RRM1 aggregates comprised disulfide-bonded oligomers, the substitution of cysteine(s) to serine(s) (C/S) resulted in unexpected acceleration of amyloid fibrils of RRM1 and disulfide-independent aggregate formation of full-length TDP-43. Notably, TDP-43 aggregates with RRM1-C/S required the C terminus, and replicated cytopathologies of ALS, including mislocalization, impaired RNA splicing, ubiquitination, phosphorylation, and motor neuron toxicity. Furthermore, RRM1-C/S accentuated inclusions of familial ALS-linked TDP-43 mutants in the C terminus. The relevance of RRM1-C/S-induced TDP-43 aggregates in ALS pathogenesis was verified by immunolabeling of inclusions of ALS patients and cultured cells overexpressing the RRM1-C/S TDP-43 with antibody targeting misfolding-relevant regions. Our results indicate that cysteines in RRM1 crucially govern the conformation of TDP-43, and aberrant self-assembly of RRM1 at amyloidogenic regions contributes to pathogenic conversion of TDP-43 in ALS.     

Physiological Characterization of an Anaerobic Ammonium-Oxidizing Bacterium Belonging to the “Candidatus Scalindua” Group

The phylogenetic affiliation and physiological characteristics (e.g., K_s and maximum specific growth rate [μ_max]) of an anaerobic ammonium oxidation (anammox) bacterium, “Candidatus Scalindua sp.,” enriched from the marine sediment of Hiroshima Bay, Japan, were investigated. “Candidatus Scalindua sp.” exhibits higher affinity for nitrite and a lower growth rate and yield than the known anammox species.     

Purification and Properties of the Trypsin Inhibitors from Buckwheat Seed

The trypsin inhibitors in buckwheat seeds were isolated by affinity chromatography on trypsin-Sepharose 4B, and the components were fractionated by chromatography on DEAE-Sepharose CL-6B. The major components, inhibitors I, II and III, were found to be homogeneous proteins with molecular weight of about 8,000. Trypsin inhibitory activity was more pronounced than the chymotrypsin inhibitory activity in all the inhibitor preparation obtained. The three major inhibitors had similar amino acid compositions and had no detectable amounts of tryptophan and carbohydrate. A high level of acidic and basic amino acid residues and a low level of methionine, tyrosine and phenylalanine residues characterized the inhibitors. Although the inhibitors I and II were particularly thermostable, inhibitor III, the most abundant component, was shown to be relatively heat-labile.     

N-Carboxymethyl-l-serine,a New Acidic Amino Acid from Asparagus (Asparagus officinalis) Shoots

A strongly acidic amino acid—N-carboxymethyl-L-serine—, not previously known in nature, has been isolated from asparagus (Asparagus officinalis) shoots. Some unique properties of this amino acid, such as a much bigger mobility to anode on high voltage paper electrophoresis (pH 3.6) than aspartic acid and characteristic changes of NMR spectra in aqueous solution with various pD, were discussed in relation to its structure.     

Purification and Properties of an S-PI(Pepstatin Ac)-insensitive Carboxyl Proteinase from a Xanthomonas sp. Bacterium

A S-PI(Pepstatin Ac)-insensitive carboxyl proteinase was found in culture filtrate of a Xanthomonas sp. bacterium. The carboxyl proteinase was highly purified and about 100 mg of the enzyme was obtained from 601 of culture filtrate, with a recovery of 25%. The optimum condition for the action of the purified enzyme toward casein was approx. pH 2.7 and its activity was not inhibited by any of such carboxyl proteinase inhibitors as Pepstatin, S-PI, and DAN but EPNP inhibited it. Such behavior of the enzyme against inhibitors resembles that of Pseudomonas sp. carboxyl proteinase, the first found from a bacterium. Some differences were observed, however, in their properties such as optimum pH, isoelectric point, and amino acid composition.     

Effect of Heavy Metal Ions on the Growth and Iron-oxidizing Activity of Thiobacillus ferrooxidans

Effect of heavy metal ions on the growth and the iron-oxidizing activity of Thiobacillus ferrooxidans were investigated.

Cupric, zinc, cadmium, and chromium ions had no effect on the growth and the iron-oxidizing activity of cell suspensions or cell-free extracts of the bacterium in high concentrations (10^?3~10^?2M). Lead ion delayed the start of the growth slightly in 10^?3 M, but it did not inhibit the iron-oxidizing activity of the cells in the concentration. Tin and molybdenum oxide ions inhibited both of them in the concentration above 10^?3 M.

Mercuric mercurous, and silver ions had the most harmful effect. In the concentration of 10^?3 .M, each of the cations inhibited almost completely both the growth and the iron-oxidizing activity of the cells.

In the experiments with cell-free extracts it was observed that the activity of cytochrome oxidase (cytochrome a₅₉₇) operating in the iron-oxidizing system of the bacterium was specifically inhibited with mercuric ion in the concentration above 5 × 10^?4 M.     

δ-Hydroxylysine,Canavanine and Three α-Amino Acid Amides from Ladino Clover Seed (Trifolium repens L. var. giganteum)

The antibacterial effects of salivary nitrate/nitrite on the growth of three Desulfovibrio species were examined. The bacteria did not grow on plates with ≥0.2 mM nitrate or ≥1.0 mM nitrite. They were also incubated in filter-sterilized saliva. D. desulfuricans was reduced on the order of >10² compared with the control solution (phosphate-buffered saline) in nine out of the 10 participants.