Suguru Oguri

large scale preparation of PA-oligosaccharides from glycoproteins using an improved extraction method

We have developed a new method for the large scale preparation of pyridylaminated (PA-) oligosaccharides from glycoproteins. Phenol/chloroform extration was adapted for the removal of protein and excess 2-aminopyridine, improving the efficiency of preparation. From a 2.5 g sample of human apo-transferrin, 25–30 μmol of agalacto biantennary PA-oligosaccharide could be obtained. By increasing the concentration of PA-oligosaccharide substrate, we were able to detect a very low level ofN-acetylglucosaminlytransferase IV activity in CHO cell extracts.

Molecular Characterization of Maize Acetylcholinesterase. A Novel Enzyme Family in the Plant Kingdom

Acetylcholinesterase (AChE) has been increasingly recognized in plants by indirect evidence of its activity. Here, we report purification and cloning of AChE from maize (Zea mays), thus providing to our knowledge the first direct evidence of the AChE molecule in plants. AChE was identified as a mixture of disulfide- and noncovalently linked 88-kD homodimers consisting of 42- to 44-kD polypeptides. The AChE hydrolyzed acetylthiocholine and propyonylthiocholine, but not S-butyrylthiocholine, and the AChE-specific inhibitor neostigmine bromide competitively inhibited its activity, implying that maize AChE functions in a similar manner as the animal enzyme. However, kinetic analyses indicated that maize AChE showed a lower affinity to substrates and inhibitors than animal AChE. The full-length cDNA of maize AChE gene is 1,471 nucleotides, which encode a protein having 394 residues, including a signal peptide. The deduced amino acid sequence exhibited no apparent similarity with that of the animal enzyme, although the catalytic triad was the same as in the animal AChE. In silico screening indicated that maize AChE homologs are widely distributed in plants but not in animals. These findings lead us to propose that the AChE family, as found here, comprises a novel family of the enzymes that is specifically distributed in the plant kingdom.

Analysis of sugar chain-binding specificity of tomato lectin using lectin blot: recognition of high mannose-type N-glycans produced by plants and yeast

The sugar chain-binding specificity of tomato lectin (LEA) against glycoproteins was investigated qualitatively using lectin blot analysis. Glycoproteins containing tri- and tetra-antennary complex-type N-glycans were stained with LEA. Unexpectedly, glycoproteins containing high mannose-type N-glycans and a horseradish peroxidase were stained with LEA. LEA blot analysis of the glycoproteins accompanied by treatment with exoglycosidase revealed that the binding site of LEA for the complex-type N-glycans was the N-acetyllactosaminyl side chains, whereas the proximal chitobiose core appeared to be the binding site of LEA for high mannose-type N-glycans. Despite these results, the glycoproteins did not inhibit the hemagglutinating activity of LEA. Among the chitin-binding lectins compared, potato tuber lectin showed specificity similar to LEA on lectin blot analysis, while Datura stramonium lectin and wheat germ agglutinin (WGA) did not interact with glycoproteins containing high mannose-type N-glycans, except that RNase B was stained by WGA.Based on these observations, LEA blot analysis was applied to sugar chain analysis of tomato glycoproteins. The most abundant LEA-reactive glycoprotein was purified from the exocarp of ripe tomato fruits, and was identified as the tomato anionic peroxidase1 (TAP1). These results suggest that LEA interacts with glycoproteins produced by tomatoes, which participate in biological activities in tomato plants.

Kinetic properties and substrate specificities of two recombinant human N-acetylglucosaminyltransferase-IV isozymes

N-acetylglucosaminyltransferase (GnT)-IV catalyzes the formation of the GlcNAcβ1-4 branch on the GlcNAcβ1-2Manα1-3 arm of the core structure of N-glycans. Two human GnT-IV isozymes (GnT-IVa and GnT-IVb) had been identified, which exhibit different expression profiles among human tissues and cancer cell lines. To clarify the enzymatic properties of the respective enzymes, their kinetic parameters were determined using recombinant full-length enzymes expressed in COS7 cells. The Km of human GnT-IVb for UDP-GlcNAc was estimated to be 0.24 mM, which is 2-fold higher than that of human GnT-IVa. The Km values of GnT-IVb for pyridylaminated (PA) acceptor sugar chains with different branch numbers were 3- to 6-fold higher than those of GnT-IVa. To compare substrate specificities more precisely, we generated recombinant soluble enzymes of human GnT-IVa and GnT-IVb with N-terminal flag tags. Both enzymes showed similar substrate specificities as determined using fourteen PA-sugar chains. They preferred complex-type N-glycans over hybrid-types. Among the complex-type N-glycans tested, the relative activities of both enzymes were increased in proportion to the number of GlcNAc branches on the Man α1-6 arm. The Man α1-6 arm of the acceptors was not essential for their activities because a linear pentasaccharide lacking this arm, GlcNAcβ1-2Manα1-3Manβ1-4GlcNAcβ1-4 GlcNAc-PA, was a substrate for both enzymes. These results indicate that human GnT-IVb exhibits the same acceptor substrate specificities as human GnT-IVa, although GnT-IVb has lower affinities for donors or acceptors than GnT-IVa. This suggests that GnT-IVa is more active than GnT-IVb under physiological conditions and that it primarily contributes to the biosynthesis of N-glycans.

Molecular cloning of acetylcholinesterase gene from Salicornia europaea L.

“Salicornia europaea” increases acetylcholinesterase (AChE) accompanied by salt accumulation during their growth. The plant acetylcholine (ACh)-mediated system in Salicornia could be responsible for transport of ions through channels in a manner similar to the animal systems. In this study, Salicornia AChE gene was identified by RT-PCR using degenerate primers designed based on previously cloned maize and siratro AChE genes. The full-length cDNA of Salicornia AChE was 1,536 nucleotides, encoding a 387-residue protein that includes a 28-residue signal sequence. In silico research presumed that Salicornia AChE is targeted to the secretory pathway via the endoplasmic reticulum.

Molecular Structure and Properties of Lectin from Tomato Fruit

A cDNA encoding tomato fruit lectin was cloned from an unripe cherry-tomato fruit cDNA library. The isolated lectin cDNA contained an open reading frame encoding 365 amino acids, including peptides that were sequenced. The deduced sequence consisted of three distinct domains: (i) an N-terminal short extensin-like domain; (ii) a Cys-rich carbohydrate binding domain composed of four almost identical chitin-binding domains; (iii) an internal extensin-like domain of 101 residues containing 15 SerPro4 motifs inserted between the first and second chitin-binding domains. The molecular weight of the lectin was 65,633 and that of the deglycosylated lectin was 32,948, as determined by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS). This correlated with the estimated molecular weight of the deduced sequence. Recombinant tomato lectin expressed in Pichia pastoris possessed chitin-binding but not hemagglutinating activity. These findings confirmed that the cDNA encoded tomato lectin.

Kunitz soybean trypsin inhibitor is modified at its C-terminus by novel soybean thiol protease (protease T1).

Abstract Kunitz soybean trypsin inhibitor (KSTI) is hydrolyzed during seed germination to yield amino acids needed to support initial seedling growth. The type of KSTI from Glycine max (L.) Merrill cv. Toyokomachi is KSTI-Ti b. The KSTI-Ti b from 4-day-old post-germination cotyledons (KSTI-Ti b’) has 3 or 4 amino acid residues cleaved off at the C-terminus. This KSTI modification is important to understand the mechanism of degradation in seed reserve proteins by proteases. Protease K1 also cleaves amino acid residues at the C-terminus of KSTI but it removes 5 amino acid residues. Therefore, we presumed the KSTI-Ti b’ was produced by a protease other than protease K1. In this study, the protease T1 responsible for cleavage of KSTI-Ti b at the C-terminus was purified. The enzyme was estimated to have a molecular mass of 33 kDa from its mobility on SDS-PAGE gels. The N-terminal amino acid sequence of the purified protease T1 corresponded to amino acids Phe-73 to Phe-92 of both thiol protease isoforms A and B from the soybean leaf, and shared 83% identity with the partial amino acid sequence of the membrane-associated cysteine protease from mung bean seedlings, a protease known to perform post-translational cleavage of C-terminal peptides of target proteins. Finally, this enzyme was shown to convert KSTI-Ti b to KSTI-Ti b’.

Yeast functional screen to identify genes conferring salt stress tolerance in Salicornia europaea.

Salinity is a critical environmental factor that adversely affects crop productivity. Halophytes have evolved various mechanisms to adapt to saline environments. Salicornia europaea L. is one of the most salt-tolerant plant species. It does not have special salt-secreting structures like a salt gland or salt bladder, and is therefore a good model for studying the common mechanisms underlying plant salt tolerance. To identify candidate genes encoding key proteins in the mediation of salt tolerance in S. europaea, we performed a functional screen of a cDNA library in yeast. The library was screened for genes that allowed the yeast to grow in the presence of 1.3 M NaCl. We obtained three full-length S. europaea genes that confer salt tolerance. The genes are predicted to encode (1) a novel protein highly homologous to thaumatin-like proteins, (2) a novel coiled-coil protein of unknown function, and (3) a novel short peptide of 32 residues. Exogenous application of a synthetic peptide corresponding to the 32 residues improved salt tolerance of Arabidopsis. The approach described in this report provides a rapid assay system for large-scale screening of S. europaea genes involved in salt stress tolerance and supports the identification of genes responsible for such mechanisms. These genes may be useful candidates for improving crop salt tolerance by genetic transformation.

Datura stramonium agglutinin: Cloning, molecular characterization and recombinant production in Arabidopsis thaliana

Datura stramonium seeds contain at least three chitin-binding isolectins [termed Datura stramonium agglutinin (DSA)] as homo- or heterodimers of A and B subunits. We isolated a cDNA encoding isolectin B (DSA-B) from an immature fruit cDNA library; this contained an open reading frame encoding 279 deduced amino acids, which was confirmed by partial sequencing of the native DSA-B peptide. The sequence consisted of: (i) a cysteine (Cys)-rich carbohydrate-binding domain composed of four conserved chitin-binding domains and (ii) an extensin-like domain of 37 residues containing four SerPro4-6 motifs that was inserted between the second and third chitin-binding domains (CBDs). Although each chitin-binding domain contained eight conserved Cys residues, only the second chitin-binding domain contained an extra Cys residue, which may participate in dimerization through inter-disulfide bridge formation. Using matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry, the molecular mass of homodimeric lectin composed of two B-subunits was determined as 68,821 Da. The molecular mass of the S-pyridilethylated B-subunit were found to be 37,748 Da and that of the de-glycosylated form was 26,491 Da, which correlated with the molecular weight estimated from the deduced sequence. Transgenic Arabidopsis plants overexpressing the dsa-b demonstrated hemagglutinating activity. Recombinant DSA-B was produced as a homodimeric glycoprotein with a similar molecular mass to that of the native form. Moreover, the N-terminus of the purified recombinant DSA-B protein was identical to that of the native DSA-B, confirming that the cloned cDNA encoded DSA-B.

N -Acetylglucosaminyltransferase (GnT) Assays Using Fluorescent Oligosaccharide Acceptor Substrates: GnT-III, IV, V, and IX (GnT-Vb)

Determining glycosyltransferase activities gives a clue for better understanding an underlying mechanism for glycomic alterations of carrier molecules. N-glycan branch formation is concertedly regulated by cooperative and competitive activities of N-acetylglucosaminyltransferases (GnTs). Here, we describe methods for large scale preparation of the oligosaccharide acceptor substrate, fluorescence-labeling of oligosaccharides by pyridylamination, quality control, and reversed phase HPLC-based measurement of GnT activities including GnT-III, IV, V, and IX.