Takako Hirano

Multicolor Imaging of Endoplasmic Reticulum-Located Esterase As a Prodrug Activation Enzyme

The carboxylesterase families of enzymes are key participants in phase I drug metabolism processes. Carboxylesterase families 1 and 2 are of particular clinical relevance. These enzymes produce endoplasmic reticulum localization signals, are primarily localized in the endoplasmic reticulum, and hydrolyze a wide range of ester-containing prodrugs into an activated form. In order to detect enzymes belonging to both families, we developed an optical multicolor imaging technique, which provides a distinct color window for multicolor imaging. This technique required the design and synthesis of three new mechanistic colored probes that fluoresce red, green, or blue and are based on the quinone methide cleavage process. These activity-based probes allow rapid and clear visualization with high specificity against the endoplasmic reticulum in cultured cells based on endoplasmic reticulum localized esterases including both families of carboxylesterase enzymes.

Heterodisaccharide 4-O-(N-acetyl-β-D-glucosaminyl)-D-glucosamine is a specific inducer of chitinolytic enzyme production in Vibrios harboring chitin oligosaccharide deacetylase genes

Vibrio parahaemolyticus KN1699 produces 4-O-(N-acetyl-beta-d-glucosaminyl)-d-glucosamine (GlcNAc-GlcN) as a major end product from chitin using two extracellular hydrolases: glycoside hydrolase family 18 chitinase, which produces (GlcNAc)(2) from chitin, and carbohydrate esterase (CE) family 4 chitin oligosaccharide deacetylase (COD), which hydrolyzes the N-acetyl group at the reducing-end GlcNAc residue of (GlcNAc)(2). In this study, we clarified that this heterodisaccharide functions as an inducer of the production of the two above-mentioned chitinolytic enzymes, particularly chitinase. Similar results for chitinase production were obtained with other chitin-decomposing Vibrio strains harboring the CE family 4 COD gene; however, such an increase in chitinase production was not observed in chitinolytic Vibrio strains that did not harbor the COD gene. These results suggest that GlcNAc-GlcN is a unique inducer of chitinase production in Vibrio bacteria that have the COD-producing ability and that the COD involved in the synthesis of this signal compound is one of the key enzymes in the chitin catabolic cascade of these bacteria.

Crystal structure of oxidized cytochrome c6A from Arabidopsis thaliana

Compared with algal and cyanobacterial cytochrome c 6, cytochrome c 6A from higher plants contains an additional loop of 12 amino acid residues. We have determined the first crystal structure of cytochrome c 6A from Arabidopsis thaliana at 1.5 Å resolution in order to help elucidate its function. The overall structure of cytochrome c 6A follows the topology of class I c‐type cytochromes in which the heme prosthetic group covalently binds to Cys16 and Cys19, and the iron has octahedral coordination with His20 and Met60 as the axial ligands. Two cysteine residues (Cys67 and Cys73) within the characteristic 12 amino acids loop form a disulfide bond, contributing to the structural stability of cytochrome c 6A. Our model provides a chemical basis for the known low redox potential of cytochrome c 6A which makes it an unsuitable electron carrier between cytochrome b 6 f and PSI.

Synthesis of β-D-fructofuranosyl-(2→1)-2-acetamido-2-deoxy-α-D-glucopyranoside (N-acetylsucrosamine) using β-fructofuranosidase-containing Aspergillus oryzae mycelia as a whole-cell catalyst.

Using soft granules consisting of Celite 535 and dried Aspergillus oryzae NBRC100959 mycelia containing β-fructofuranosidase as a whole-cell catalyst, N-acetylsucrosamine [β-D-fructofuranosyl-(2→1)-2-acetamido-2-deoxy-α-D-glucopyranoside] was produced from sucrose and 2-acetamido-2-deoxy-D-glucose by enzymatic transfructosylation. The isolated yield of N-acetylsucrosamine from the reaction mixture was 22.1% (from sucrose). The result of N-terminal amino acid sequence analysis indicated that the enzyme involved in the synthesis of N-acetylsucrosamine is a product from gene (NCBI accession number; NW_001884675, locus tag; AOR_1_1114084) encoding putative β-fructofuranosidase on chromosome 6 of strain NBRC100959. The N-acetylsucrosamine we produced is highly soluble in water and is more stable in acidic solution than sucrose. The disaccharide was also produced using dried mycelia prepared from another A. oryzae strains.

Structure-based analysis of domain function of chitin oligosaccharide deacetylase from Vibrio parahaemolyticus

The X‐ray crystal structure of chitin oligosaccharide deacetylase from Vibrio parahaemolyticus (Vp‐COD) was determined at an 1.35 Å resolution. The amino acid sequence and structure of Vp‐COD show that the enzyme comprises one polysaccharide deacetylase domain (PDD) and two carbohydrate‐binding domains (CBDs). On the basis of a chitin‐binding assay with Vp‐COD and its CBDs‐deleted mutant, it was confirmed that CBDs can adhere to chitin. The catalytic activity of the CBDs‐deleted mutant was only mildly depressed compared with that of Vp‐COD, indicating that CBDs are unlikely to affect the configuration of the active center residues in active site of PDD.

Heterodisaccharide 4‐O‐(N‐acetyl‐β‐d‐glucosaminyl)‐d‐glucosamine is an effective chemotactic attractant for Vibrio bacteria that produce chitin oligosaccharide deacetylase

Aims:  To investigate the attractant effect of 4‐O‐(N‐acetyl‐β‐d‐glucosaminyl)‐d‐glucosamine (GlcNAc‐GlcN) in the chemotaxis of Vibrio bacteria that produce carbohydrate esterase (CE) family 4 chitin oligosaccharide deacetylase (COD), an enzyme that catalyzes the production of GlcNAc‐GlcN from N,N′‐diacetylchitobiose (GlcNAc)2.

Production and Secretion of a Recombinant Vibrio parahaemolyticus Chitinase by Escherichia coli and Its Purification from the Culture Medium

An open reading frame encoding the chitinase gene and its signal sequence was cloned from the Vibrio parahaemolyticus KN1699 genome. An expression plasmid containing the gene was introduced into Escherichia coli cells, and recombinant chitinase (Pa-rChi) was produced and secreted into the culture medium with the aid of the signal peptide. Pa-rChi was purified and its substrate specificity was determined.

Enzymatic synthesis of novel oligosaccharides from N-acetylsucrosamine and melibiose using Aspergillus niger α-galactosidase, and properties of the products

Two kinds of oligosaccharides, N-acetylraffinosamine (RafNAc) and N-acetylplanteosamine (PlaNAc), were synthesized from N-acetylsucrosamine and melibiose using the transgalactosylation activity of Aspergillus niger α-galactosidase. RafNAc and PlaNAc are novel trisaccharides in which d-glucopyranose residues in raffinose (Raf) and planteose are replaced with N-acetyl-d-glucosamine. These trisaccharides were more stable in acidic solution than Raf. RafNAc was hydrolyzed more rapidly than Raf by α-galactosidase of green coffee bean. In contrast, RafNAc was not hydrolyzed by Saccharomyces cerevisiae invertase, although Raf was hydrolyzed well by this enzyme. These results indicate that the physicochemical properties and steric structure of RafNAc differ considerably from those of Raf. Graphical Abstract Two kinds of novel trisaccharides were synthesized from N-acetylsucrosamine and melibiose, using transgalactosylation action of Aspergillus niger α-galactosidase.

Enzymatic synthesis of novel oligosaccharides from N-acetylsucrosamine using β-fructofuranosidase from Aspergillus oryzae.

Mycelia of Aspergillus oryzae NBRC100959 contain 2 types of β-fructofuranosidases, transfructosylation-catalyzing enzyme (βFFaseI), and hydrolysis-catalyzing enzyme (βFFaseII). Using βFFaseI extracted from the mycelia of strain NBRC100959, two novel oligosaccharides consisting of GlcNAc and fructose, β-d-fructofuranosyl-(2→1)-β-d-fructofuranosyl-(2↔1)-2-acetamido-2-deoxy-α-d-glucopyranoside (N-acetyl-1-kestosamine, 1-KesNAc) and β-d-fructofuranosyl-(2→1)-β-d-fructofuranosyl-(2→1)-β-d-fructofuranosyl-(2↔1)-2-acetamido-2-deoxy-α-d-glucopyranoside (N-acetylnystosamine, NysNAc), were synthesized from β-d-fructofuranosyl-(2↔1)-2-acetamido-2-deoxy-α-d-glucopyranoside (N-acetylsucrosamine, SucNAc). We next planned to synthesize 1-KesNAc and NysNAc using A. oryzae mycelia. However, it was thought that the presence of βFFaseII is disadvantageous for the production of these oligosaccharides by βFFaseI, because βFFaseII hydrolyzed 1-KesNAc and NysNAc. We succeeded to produce A. oryzae mycelia containing βFFaseI as the major β-fructofuranosidase, by increasing sucrose concentration in the culture medium. Then, using a dried sample of these A. oryzae mycelia, reaction for the oligosaccharide production was performed. As the results, 190mg of 1-KesNAc and 60mg of NysNAc were obtained from 0.6g of SucNAc. This whole-cell catalysis method facilitates the synthesis of 1-KesNAc and NysNAc because extraction and purification of βFFaseI from mycelia are unnecessary.

Crystallization and Structural Analysis of Cytochrome c 6 from the Diatom Phaeodactylum tricornutum at 1.5 Å Resolution

We determined for the first time the crystal structure of diatom cytochrome c 6 from Phaeodactylum tricornutum at 1.5 Å resolution. The overall structure of the protein was classified as a class I c-type cytochrome. The physicochemical properties of the protein were examined by denaturation with guanidine hydrochloride and urea, and compared with those of other algal cytochrome c 6.