Yoshimitsu Takakura

Tamavidins – novel avidin‐like biotin‐binding proteins from the Tamogitake mushroom

Novel biotin‐binding proteins, referred to herein as tamavidin 1 and tamavidin 2, were found in a basidiomycete fungus, Pleurotus cornucopiae, known as the Tamogitake mushroom. These are the first avidin‐like proteins to be discovered in organisms other than birds and bacteria. Tamavidin 1 and tamavidin 2 have amino acid sequences with 31% and 36% identity, respectively, to avidin, and 47% and 48% identity, respectively, to streptavidin. Unlike any other biotin‐binding proteins, tamavidin 1 and tamavidin 2 are expressed as soluble proteins at a high level in Escherichia coli. Recombinant tamavidin 2 was purified as a tetrameric protein in a single step by 2‐iminobiotin affinity chromatography, with a yield of 5 mg per 100 mL culture of E. coli. The kinetic parameters measured by a BIAcore biosensor indicated that recombinant tamavidin 2 binds biotin with high affinity, in a similar manner to binding by avidin and streptavidin. The overall crystal structure of recombinant tamavidin 2 is similar to that of avidin and streptavidin. However, recombinant tamavidin 2 is immunologically distinct from avidin and streptavidin. Tamavidin 2 and streptavidin are very similar in terms of the arrangement of the residues interacting with biotin, but different with regard to the number of hydrogen bonds to biotin carboxylate. Recombinant tamavidin 2 is more stable than avidin and streptavidin at high temperature, and nonspecific binding to DNA and human serum by recombinant tamavidin 2 is lower than that for avidin. These findings highlight tamavidin 2 as a probable powerful tool, in addition to avidin and streptavidin, in numerous applications of biotin‐binding proteins.

Expression of a bacterial flagellin gene triggers plant immune responses and confers disease resistance in transgenic rice plants.

Flagellin is a component of bacterial flagella and acts as a proteinaceous elicitor of defence responses in organisms. Flagellin from a phytopathogenic bacterium, Acidovorax avenae strain N1141, induces immune responses in suspension-cultured rice cells. To analyse the function of flagellin in rice, we fused the N1141 flagellin gene to the cauliflower mosaic virus 35S promoter and introduced it into rice. Many of the resulting transgenic rice plants accumulated flagellin at various levels. The transgenic rice developed pale spots in the leaves. The expression of a defence-related gene for phenylalanine ammonia-lyase was induced in the transgenic plants, and H(2)O(2) production and cell death were observed in some plants with high levels of gene expression, suggesting that the flagellin triggers immune responses in the transgenic rice. Transgenic plants inoculated with Magnaporthe grisea, the causal agent of rice blast, showed enhanced resistance to blast, suggesting that the flagellin production confers disease resistance in the transgenic rice.

Purification, Cloning, and Expression of an α/β-Galactoside α-2,3-Sialyltransferase from a Luminous Marine Bacterium, Photobacterium phosphoreum

A novel sialyltransferase, α/β-galactoside α-2,3-sialyltransferase, was purified from the cell lysate of a luminous marine bacterium, Photobacterium phosphoreum JT-ISH-467, isolated from the Japanese common squid (Todarodes pacificus). The gene encoding the enzyme was cloned from the genomic library of the bacterium using probes derived from the NH2-terminal and internal amino acid sequences. An open reading frame of 409 amino acids was identified, and the sequence had 32% identity with that of β-galactoside α-2,6-sialyltrasferase in Photobacterium damselae JT0160. DNA fragments that encoded the full-length protein and a protein that lacked the sequence between the 2nd and 24th residues at the NH2 terminus were amplified by polymerase chain reactions and cloned into an expression vector. The full-length and truncated proteins were expressed in Escherichia coli, producing active enzymes of 0.25 and 305 milliunits, respectively, per milliliter of the medium in the lysate of E. coli. The truncated enzyme was much more soluble without detergent than the full-length enzyme. The enzyme catalyzed the transfer of N-acetylneuraminic acid from CMP-N-acetylneuraminic acid to disaccharides, such as lactose and N-acetyllactosamine, with low apparent Km and to monosaccharides, such as α-methyl-galactopyranoside and β-methyl-galactopyranoside, with much lower apparent Km. Thus, this sialyltransferase is unique and should be very useful for achieving high productivity in E. coli with a wide substrate range.

Binary Vectors and Super-binary Vectors

A binary vector is a standard tool in the transformation of higher plants mediated by Agrobacterium tumefaciens. It is composed of the borders of T-DNA, multiple cloning sites, replication functions for Escherichia coli and A. tumefaciens, selectable marker genes, reporter genes, and other accessory elements that can improve the efficiency of and/or give further capability to the system. A super-binary vector carries additional virulence genes from a Ti plasmid, and exhibits very high frequency of transformation, which is valuable for recalcitrant plants such as cereals. A number of useful vectors are widely circulated. Whereas vectors with compatible selectable markers and convenient cloning sites are usually the top criteria when inserting gene fragments shorter than 15 kb, the capability of maintaining a large DNA piece is more important for consideration when introducing DNA fragments larger than 15 kb. Because no vector is perfect for every project, it is recommended that modification or construction of vectors should be made according to the objective of the experiments. Existing vectors serve as good sources of components.

Purification, Characterization, and Molecular Cloning of a Pyranose Oxidase from the Fruit Body of the Basidiomycete, Tricholoma matsutake

A new H2O2-generating pyranose oxidase was purified as a strong antifungal protein from an arbuscular mycorrhizal fungus, Tricholoma matsutake. The protein showed a molecular mass of 250 kDa in gel filtration, and probably consisted of four identical 62 kDa subunits. The protein contained flavin moiety and it oxidized D-glucose at position C-2. H2O2 and D-glucosone produced by the pyranose oxidase reaction showed antifungal activity, suggesting these compounds were the molecular basis of the antifungal property. The V max, K m, and k cat for D-glucose were calculated to be 26.6 U/mg protein, 1.28 mM, and 111/s, respectively. The enzyme was optimally active at pH 7.5 to 8.0 and at 50°C. The preferred substrate was D-glucose, but 1,5-anhydro-D-glucitol, L-sorbose, and D-xylose were also oxidized at a moderate level. The cDNA encodes a protein consisting of 564 amino acids, showing 35.1% identity to Coriolus versicolor pyranose oxidase. The recombinant protein was used for raising the antibody.

Tamavidin, a versatile affinity tag for protein purification and immobilization

Tamavidin 2 is a fungal avidin-like protein that binds biotin with high affinity and is highly produced in soluble form in Escherichia coli. By contrast, widely used biotin-binding proteins avidin and streptavidin are rarely produced in soluble form in E. coli. In this study, we describe an efficient system for one-step purification and immobilization of recombinant proteins using tamavidin 2 as an affinity tag. A bacterial sialyltransferase and soybean agglutinin were fused to tamavidin 2 and expressed in E. coli and tobacco BY-2 cells, respectively. High-level expressions of the fusion proteins were detected (80 mg l(-1)E. coli culture for bacterial sialyltransferase-tamavidin 2 and 2 mg l(-1) BY-2 cell culture for soybean agglutinin-tamavidin 2). To immobilize and purify the fusion proteins, biotinylated magnetic microbeads were incubated with the soluble extract from each recombinant host producing the fusion protein and then washed thoroughly. As the result, both fusion proteins were immobilized tightly on the microbeads without substantial loss of activity and simultaneously highly purified (90-95% purity) on the microbeads. Biotin with a longer linker contributed to higher affinity between the fusion protein and biotin. These results suggest that tamavidin fusion technology is a powerful tool for production, purification, and immobilization of recombinant proteins.

Crystal structure of α/β-galactoside α2,3-sialyltransferase from a luminous marine bacterium, Photobacterium phosphoreum

α/β‐Galactoside α2,3‐sialyltransferase produced by Photobacterium phosphoreum JT‐ISH‐467 is a unique enzyme that catalyzes the transfer of N‐acetylneuraminic acid residue from cytidine monophosphate N‐acetylneuraminic acid to acceptor carbohydrate groups. The enzyme recognizes both mono‐ and di‐saccharides as acceptor substrates, and can transfer Neu5Ac to both α‐galactoside and β‐galactoside, efficiently. To elucidate the structural basis for the broad acceptor substrate specificity, we determined the crystal structure of the α2,3‐sialyltransferase in complex with CMP. The overall structure belongs to the glycosyltransferase‐B structural group. We could model a reasonable active conformation structure based on the crystal structure. The predicted structure suggested that the broad substrate specificity could be attributed to the wider entrance of the acceptor substrate binding site.

An α2,6-sialyltransferase cloned from Photobacterium leiognathi strain JT-SHIZ-119 shows both sialyltransferase and neuraminidase activity

We cloned, expressed, and characterized a novel beta-galactoside alpha2,6-sialyltransferase from Photobacterium leiognathi strain JT-SHIZ-119. The protein showed 56-96% identity to the marine bacterial alpha2,6-sialyltransferases classified into glycosyltransferase family 80. The sialyltransferase activity of the N-terminal truncated form of the recombinant enzyme was 1477 U/L of Escherichia coli culture. The truncated recombinant enzyme was purified as a single band by sodium dodecyl sulfate polyacrylamide gel electrophoresis through 3 column chromatography steps. The enzyme had distinct activity compared with known marine bacterial alpha2,6-sialyltransferases. Although alpha2,6-sialyltransferases cloned from marine bacteria, such as Photobacterium damselae strain JT0160, P. leiognathi strain JT-SHIZ-145, and Photobacterium sp. strain JT-ISH-224, show only alpha2,6-sialyltransferase activity, the recombinant enzyme cloned from P. leiognathi strain JT-SHIZ-119 showed both alpha2,6-sialyltransferase and alpha2,6-linkage-specific neuraminidase activity. Our results provide important information toward a comprehensive understanding of the bacterial sialyltransferases belonging to the group 80 glycosyltransferase family in the CAZy database.

Intercellular Production of Tamavidin 1, a Biotin-Binding Protein from Tamogitake Mushroom, Confers Resistance to the Blast Fungus Magnaporthe oryzae in Transgenic Rice

The blast fungus Magnaporthe oryzae, one of the most devastating rice pathogens in the world, shows biotin-dependent growth. We have developed a strategy for creating disease resistance to M. oryzae whereby intercellular production of tamavidin 1, a biotin-binding protein from Pleurotus cornucopiae occurs in transgenic rice plants. The gene that encodes tamavidin 1, fused to the sequence for a secretion signal peptide derived from rice chitinase gene, was connected to the Cauliflower mosaic virus 35S promoter, and the resultant construct was introduced into rice. The tamavidin 1 was accumulated at levels of 0.1–0.2% of total soluble leaf proteins in the transgenic rice and it was localized in the intercellular space of rice leaves. The tamavidin 1 purified from the transgenic rice was active, it bound to biotin and inhibited in vitro growth of M. oryzae by causing biotin deficiency. The transgenic rice plants showed a significant resistance to M. oryzae. This study shows the possibility of a new strategy to engineer disease resistance in higher plants by taking advantage of a pathogen’s auxotrophy.

Tamavidin 2-REV: an engineered tamavidin with reversible biotin-binding capability.

A biotin-binding protein with reversible biotin-binding capability is of great technical value in the affinity purification of biotinylated biomolecules. Although several proteins, chemically or genetically modified from avidin or streptavidin, with reversible biotin-binding have been reported, they have been problematic in one way or another. Tamavidin 2 is a fungal protein similar to avidin and streptavidin in biotin-binding. Here, a mutein, tamavidin 2-REV, was engineered from tamavidin 2 by replacing the serine at position 36 (S36) with alanine. S36 is thought to form a hydrogen bond with biotin in tamavidin 2/biotin complexes and two hydrogen bonds with V38 within the protein. Tamavidin 2-REV bound to biotin-agarose and was eluted with excess free biotin at a neutral pH. In addition, the model substrate biotinylated bovine serum albumin was efficiently purified from a crude extract from Escherichia coli by means of single-step affinity chromatography with tamavidin 2-REV-immobilized resin. Tamavidin 2-REV thus demonstrated reversible biotin-binding capability. The Kd value of tamavidin 2-REV to biotin was 2.8-4.4×10(-7)M.Tamavidin 2-REV retained other convenient characteristics of tamavidin 2, such as high-level expression in E. coli, resistance to proteases, and a neutral isoelectric point, demonstrating that tamavidin 2-REV is a powerful tool for the purification of biotinylated biomolecules.