Kaoru Kojima

Ion-spray mass spectrometric analysis of glycosaminoglycan oligosaccharides

Oligosaccharides from hyaluronic acid and chondroitin 6-sulfate were prepared by digestion with testicular hyaluronidase and separated according to their degree of polymerization by gel-permeation chromatography. These materials were successively analyzed by negative-mode ion-spray mass spectrometry with an atmospheric-pressure ion source. An ion-spray interface was used to produce ions via the ion evaporation process, producing mass spectra containing a series of molecular species carrying multiple charges. Using two adjacent multiply charged molecular ions, the exact molecular weights up to the tetradecasaccharide were calculated with a precision of ±1 dalton. This type of mass spectrometry was also demonstrated to be feasible for the analysis of mixtures of oligosaccharides, including tetra-, hexa-, octa- and decasaccharides, from hyaluronic acid or chondroitin 6-sulfate without separation. Ion-spray mass spectrometry was thus shown to be applicable to the structural analysis of oligosaccharides from glycosaminoglycans.

Marine bacterial sulfated fucoglucuronomannan (SFGM) lyase digests brown algal SFGM into trisaccharides

Three kinds of trisaccharides were prepared by digesting fucoidan from the brown alga Kjellmaniella crassifolia, with the extracellular enzymes of the marine bacterium Fucobacter marina. Their structures were determined as Δ4,5GlcpUA1-2(L-Fucp(3-O-sulfate)α1-3)D-Manp, Δ4,5GlcpUA1-2(L-Fucp(3-O-sulfate)α1-3)D-Manp(6-O-sulfate), and Δ4,5GlcpUA1-2(L-Fucp(2,4-O-disulfate)α1-3)D-Manp(6-O-sulfate), which indicated the existence of a novel polysaccharide in the fucoidan and a novel glycosidase in the extracellular enzymes. In order to determine the complete structure of the polysaccharide and the reaction mechanism of the glycosidase, the fucoidan was partially hydrolyzed to obtain glucuronomannan, which is the putative backbone of the polysaccharide, and its sugar sequence was determined as (-4-D-GlcpUAβ1-2D-Manpα1-)n, which disclosed that the main structure of the polysaccharide is (-4-D-GlcpUAβ1-2(L-Fucp(3-O-sulfate)α1-3)D-Manpα1-)n. Consequently, the glycosidase was deduced to be an endo-α-D-mannosidase that eliminatively cleaves the α-D-mannosyl linkage between D-Manp and D-GlcpUA residues in the polysaccharide and produces the above trisaccharides. The novel polysaccharide and glycosidase were tentatively named as sulfated fucoglucuronomannan (SFGM) and SFGM lyase, respectively.

Mechanism for the hydrolysis of hyaluronan oligosaccharides by bovine testicular hyaluronidase

Synthetic hyaluronan oligosaccharides with defined structures and their pyridylaminated derivatives were used to investigate the mechanism of hydrolysis of hyaluronan by bovine testicular hyaluronidase. The products of the hydrolysis were analyzed by HPLC and ion‐spray mass spectroscopy (MS). It was confirmed that the minimum substrate for bovine testicular hyaluronidase is the hyaluronan hexasaccharide, even though it is a poor substrate that is barely cleaved, even on prolonged incubation. When hyaluronan octasaccharide was the substrate, increasing amounts of tetrasaccharide and hexasaccharide were produced with increasing time of incubation. Whereas disaccharide was not detectable in the reaction mixture by HPLC, MS analysis revealed trace amounts. The data suggest that the enzyme generates a disaccharide intermediate from hyaluronan oligosaccharide, the majority of which is transferred to the nonreducing ends of other oligosaccharides, only traces being released as free disaccharide. When hyaluronan octasaccharide, with an unsaturated glucuronic acid at the nonreducing end, was used as a substrate, only a tetrasaccharide was detected by HPLC. However, MS showed that the product was a mixture of equal amounts of two tetrasaccharides, one with and the other without the unsaturated glucuronic acid. This suggests that, in the case of substrates with a double bond at the nonreducing end, a tetrasaccharide is cleaved off instead of a disaccharide. The results of the experiments with pyridylaminated oligosaccharides were entirely consistent with these conclusions, and in addition showed the importance of the reducing end of the substrate for the enzyme to recognize the length of the saccharide.

Structural Interactions in Chondroitin 4-Sulfate Mediated Adherence of Plasmodium falciparum Infected Erythrocytes in Human Placenta during Pregnancy-Associated Malaria†

Infection with Plasmodium falciparum during pregnancy results in the adherence of infected red blood cells (IRBCs) in placenta, causing pregnancy-associated malaria with severe health complications in mothers and fetuses. The chondroitin 4-sulfate (C4S) chains of very low sulfated chondroitin sulfate proteoglycans (CSPGs) in placenta mediate the IRBC adherence. While it is known that partially sulfated but not fully sulfated C4S effectively binds IRBCs, structural interactions involved remain unclear and are incompletely understood. In this study, structurally defined C4S oligosaccharides of varying sulfate contents and sizes were evaluated for their ability to inhibit the binding of IRBCs from different P. falciparum strains to CSPG purified from placenta. The results clearly show that, with all parasite strains studied, dodecasaccharide is the minimal chain length required for the efficient adherence of IRBCs to CSPG and two 4-sulfated disaccharides within this minimal structural motif are sufficient for maximal binding. Together, these data demonstrate for the first time that the C4S structural requirement for IRBC adherence is parasite strain-independent. We also show that the carboxyl group on nonreducing end glucuronic acid in dodecasaccharide motif is important for IRBC binding. Thus, in oligosaccharides containing terminal 4,5-unsaturated glucuronic acid, the nonreducing end disaccharide moiety does not interact with IRBCs due to the altered spatial orientation of carboxyl group. In such C4S oligosaccharides, 14-mer but not 12-mer constitutes the minimal motif for inhibition of IRBC binding to placental CSPG. These data have important implications for the development and evaluation of therapeutics and vaccine for placental malaria.

Novel products in hyaluronan digested by bovine testicular hyaluronidase

When the products of hyaluronan (HA) digested by bovine testicular hyaluronidase (BTH) were analyzed by high-performance liquid chromatography (HPLC), minor peaks were detected just before the main even-numbered oligosaccharide peaks. The amount of each minor peak was dependent on the reaction conditions for transglycosylation, rather than hydrolysis, by the BTH. Mainly based on HPLC and MS analysis, each minor peak was found to correspond to its oligosaccharide with one N-acetyl group removed from the reducing terminal N-acetylglucosamine. Enzymatic studies showed that the N-deacetylation activity was closely related to reaction temperature, pH, and the concentration of NaCl contained in the buffer, and glycosaminoglycan types and chain lengths of substrates. These findings strongly suggest that the N-deacetylation reaction in minor peaks was due to a novel enzyme contaminant in the BTH, N-deacetylase, that carries out N-deacetylation at the reducing terminal N-acetylglucosamine of oligosaccharides and is dependent on HA hydrolysis by BTH.

Novel proteoglycan glycotechnology: chemoenzymatic synthesis of chondroitin sulfate-containing molecules and its application

Proteoglycans consist of a protein core, with one or more glycosaminoglycan chains (i.e., chondroitin sulfate, dermatan sulfate and heparin sulfate) bound covalently to it. The glycosaminoglycan chains account for many of the functions and properties of proteoglycans. The development of proteoglycan glycotechnology to exploit the functionality of glycosaminoglycan chains is an extremely important aspect of glycobiology. Here we describe an efficient and widely applicable method for chemoenzymatic synthesis of conjugate compounds comprising intact long chondroitin sulfate (ChS) chains. An alkyne containing ChS was prepared by an enzymatic transfer reaction and linked with a chemically synthesized core compound containing an azido group using click chemistry. This method enabled highly efficient introduction of ChS into target materials. Furthermore, the ChS-introduced compounds had marked stability against proteolysis, and the chemically linked ChS chain contributed to the stability of these core compounds. We believe the present method will contribute to the development of proteoglycan glycobiology and technology.