No abstract

The hinge region of human immunoglobulin A1 (*IgA1) possesses multiple O-glycans, of which synthesis is initiated by the addition of GalNAc to serine or threonine through the activity of UDP-N-acetyl-␣-D-galactosamine:polypeptide N-acetylgalactosaminyltransferases (pp-GalNAc-Ts). We found that six pp-GalNAc-Ts, ppGalNAc-T1, -T2, -T3, -T4, -T6, and -T9, were expressed in B cells, IgA-bearing B cells, and NCI-H929 IgA myeloma cells. pp-GalNAc-T activities of these six enzymes for a synthetic IgA hinge peptide, which has nine possible O-glycosylation sites, were examined using a reversed phase-high performance liquid chromatography, a matrix-assisted laser desorption ionization time of flight mass spectrometry, and peptide sequencing analysis. pp-GalNAc-T2 showed the strongest activity transferring GalNAc to a maximum of eight positions. Other pp-GalNAc-Ts exhibited different substrate specificities from pp-GalNAc-T2; however, their activities were extremely weak. It was reported that the IgA1 hinge region possesses a maximum of five O-glycans, and their amino acid positions have been determined. We found that pp-GalNAc-T2 selectively transferred GalNAc residues to the same five positions. These results strongly suggested that pp-GalNAc-T2 is an essential enzyme for initiation of O-linked glycosylation of the IgA1 hinge region.

We found, using a BLAST search, a novel human gene (GenBank TM accession number BC029564) that possesses ␤3-glycosyltransferase motifs. The full-length open reading frame consists of 500 amino acids and encodes a typical type II membrane protein. This enzyme has a domain containing ␤1,3-glycosyltransferase motifs, which are widely conserved in the ␤1,3-galactosyltransferase and ␤1,3-N-acetylglucosaminyltransferase families. The putative catalytic domain was expressed in human embryonic kidney 293T cells as a soluble protein. Its N-acetylgalactosaminyltransferase activity was observed when N-acetylglucosamine (GlcNAc) ␤1-O-benzyl was used as an acceptor substrate. The enzyme product was determined to have a ␤1,3-linkage by NMR spectroscopic analysis, and was therefore named ␤1,3-Nacetylgalactosaminyltransferase-II (␤3GalNAc-T2). The acceptor substrate specificity of ␤3GalNAc-T2 was examined using various oligosaccharide substrates. Gal-␤1-3(GlcNAc␤1-6)GalNAc␣1-O-para-nitrophenyl (core 2-pNP) was the best acceptor substrate for ␤3GalNAc-T2, followed by GlcNAc␤1-4GlcNAc␤1-O-benzyl, and GlcNAc␤1-6GalNAc␣1-O-para-nitrophenyl (core 6-pNP), among the tested oligosaccharide substrates. Quantitative real time PCR analysis revealed that the ␤3Gal-NAc-T2 transcripts was restricted in its distribution mainly to the testis, adipose tissue, skeletal muscle, and ovary. Its putative orthologous gene, m␤3GalNAc-T2, was also found in a data base of mouse expressed sequence tags. In situ hybridization analysis with mouse testis showed that the transcripts are expressed in germ line cells. ␤3GalNAc-T2 efficiently transferred GalNAc to N-glycans of fetal calf fetuin, which was treated with neuraminidase and ␤-galactosidase. However, it showed no activity toward any glycolipid examined. Although the GalNAc␤1-3GlcNAc␤1-R structure has not been reported in humans or other mammals, we have discovered a novel human glycosyltransferase producing this structure on N-and O-glycans.

We found a novel glycosyltransferase gene having a hypothetical ␤1,4-galactosyltransferase motif (GenBank TM accession number AB081516) by a BLAST search and cloned its full-length open reading frame using the 5-rapid amplification of cDNA ends method. The truncated form was expressed in insect cells as a soluble enzyme. It transferred N-acetylgalactosamine, not galactose, to para-nitrophenyl-␤-glucuronic acid. The N-acetylgalactosamine-glucuronic acid linkage has been identified only in chondroitin sulfate; therefore, we examined its chondroitin elongation and initiation activities. N-Acetylgalactosaminyltransferase activity was observed toward chondroitin poly-and oligosaccharides, chondroitin sulfate oligosaccharides, and linkage tetrasaccharide (GlcA-Gal-Gal-Xyl-O-methoxyphenyl), and the chondroitin polysaccharide and linkage tetrasaccharide were better acceptor substrates than the others. Northern blot analysis and quantitative realtime PCR analysis revealed that its 4-kb transcripts were highly expressed in thyroid and placenta, although they were ubiquitously expressed in various tissues and cells. These results suggest that this enzyme has N-acetylgalactosaminyltransferase activity in both the elongation and initiation of chondroitin sulfate synthesis. Furthermore, we performed enzymatic synthesis of chondroitin pentasaccharide in vitro. In one tube reaction with four enzymes, ␤1,4-galactosyltransferase-VII, ␤1,3-galactosyltransferase-VI, glucuronyltransferase-I, and this enzyme, and a synthetic xylose-peptide acceptor, the structure GalNAc-GlcA-Gal-Gal-Xyl-peptide was constructed. This is the first report of a chondroitin pentasaccharide constructed with recombinant glycosyltransferases in vitro.

A sequence highly homologous to L L1,4-N-acetylgalactosaminyltransferase III (L L4GalNAc-T3) was found in a database of human expressed sequence tags. The full-length open reading frame of the gene, L L4GalNAc-T4 (GenBank accession number AB089939), was cloned using the 5P P rapid ampli¢cation of cDNA ends method. It encodes a typical type II transmembrane protein of 1039 amino acids having 42.6% identity with L L4GalNAc-T3. The recombinant enzyme transferred N-acetylgalactosamine to N-acetylglucosamine-L L-benzyl with a L L1,4-linkage to form N,NP P-diacetyllactosediamine as did L L4Gal-NAc-T3. In speci¢city toward oligosaccharide acceptor substrates, it was quite similar to L L4GalNAc-T3 in vitro, however, the tissue distributions of the two enzymes were quite di¡erent. These results indicated that the two enzymes have similar roles in di¡erent tissues.

35 S]PAPS, the highest incorporation of 35 S was observed, and digestion of the product with a mixture of heparin lyases yielded two major 35 S-labeled disaccharides, which were determined as ⌬HexA-GlcN(NS,3S,6S) and ⌬HexA(2S)-GlcN(NS,3S) by further digestion with 2-sulfatase and degradation with mercuric acetate. However, when used heparin as acceptor, we identified a highly sulfated disaccharide unit as a major product. This had a structure of ⌬HexA(2S)-GlcN(NS,3S,6S). Quantitative real-time PCR analysis revealed that 3-OST-5 was highly expressed in fetal brain, followed by adult brain and spinal cord, and at very low or undetectable levels in the other tissues. Finally, we detected a tetrasulfated disaccharide unit in bovine intestinal heparan sulfate. To our knowledge, this is the first report to describe not only the natural occurrence of tetrasulfated disaccharide unit but also the enzymatic formation of this novel structure.

No abstract

An S-alkyl-thioester-moiety-containing linker with an enhanced stability on a resin has been developed. A linker containing S-alkyl thioester with a spacer group, –CO–SC(CH3)2CH2CO–Nle–, was stable during the peptide chain elongation cycle. This thioester was stable under HF treatment conditions, and was rapidly activated by silver ions in the presence of N-hydroxysuccinimde (HONSu) to form a peptide bond. Using this linker, peptide segments covering the HU-type DNA-binding protein of Bacillus stearothermophilus (HBs), which was site-specifically labelled with 2H, 13C, and 15N, were prepared. Using these peptide segments, multi-labelled HBs was synthesized. Distinct signals of 2H, 13C, and 15N in HBs were detected by NMR spectrometry.