Ji Kang

Structural characterization of a low-molecular-weight heteropolysaccharide (glucomannan) isolated from Artemisia sphaerocephala Krasch.

Using 60% (w/v) ammonium sulfate precipitation, a heteropolysaccharide (designated 60S), with relatively low molecular weight (38.7kDa), was isolated from the seeds of Artemisiasphaerocephala Krasch. The structural properties of 60S were elucidated by partial acid hydrolysis, methylation analysis, 1D and 2D NMR spectroscopy, and MALDI-TOF-MS. The results of the partial acid hydrolysis and methylation analysis indicated that the main chain of 60S consisted of (1→4)-linked d-Manp and (1→4)-linked d-Glcp in a molar ratio of 1:1.3. Over half of the glucosyl residues in the main chain were branched at the O-6 position. The terminal sugar residues were mainly composed of T-Araf, T-Arap, T-Galp, T-GlcpA, and T-Glcp. Besides, 3-Araf and 2-Galp were also observed in comparable amounts. Based on all the aforementioned results and the data obtained by 1D and 2D NMR spectroscopy as well as MALDI-TOF-MS, a structure of 60S is proposed as follows: R could be one or some of -(3-α-Araf)(n)-(A), T-α-Galp(B), T-α-Glcp(C), T-Araf(H) or T-Arap.

Structural investigation of a glycoprotein from gum ghatti

The glycoprotein structure of gum ghatti was investigated. The covalent bonding between polysaccharides and proteins was firstly confirmed by high performance size exclusion chromatography (HPSEC) using refractive index (RI) and UV detectors. Partial acid hydrolysis and enzymatic degradation were also utilized. Several structural fragments such as AraHex2-HexA-HexNAc, Hex4HexNAc2, AraHex4HexNAc, Hex10HexNAc and Hex4HexNAc-Asn were identified from MALDI-TOF spectrum; using 1D and 2D NMR spectra, the linkage site of amino acids and polysaccharides was determined as N-linked (Hex)n-GlcNAc-Asn. Combined with the polysaccharide structure obtained before, a glycoprotein structure model was proposed. It was composed of 1,6-linked galactose backbone, which were attached by numerous of sugar side chains and peptide chains.

Study of the mechanism of formation of hyaluronan putty at pH 2.5: Part I. Experimental measurements

This paper reports on the elucidation of the possible mechanism for forming the putty structure of hyaluronan (HA) at low pH (2.5) using rheological methods. Oscillation and stress relaxation tests on a series HA putty samples containing various concentrations of salt indicated that ionic forces were not the driving force for their formation, but hydrogen bonds were responsible for driving two or more HA molecular chains together to form a three dimensional network. Our results indicated/confirmed that the carboxyl group of the glucuronic acid and acetamido group of N-acetylglucosamine moieties on two neighboring HA chains are involved in the formation of the intermolecular hydrogen bonding, which lead to the formation of the putty at pH 2.5.

A molecular modeling approach to understand the structure and conformation relationship of (GlcpA)Xylan

The structure and conformation relationships of a heteropolysaccharide (GlcpA)Xylan in terms of various molecular weights, Xylp/GlcpA ratio and the distribution of GlcpA along xylan chain were investigated using computer modeling. The adiabatic contour maps of xylobiose, XylpXylp(GlcpA) and (GlcpA)XylpXylp(GlcpA) indicated that the insertion of the side group (GlcpA) influenced the accessible conformational space of xylobiose molecule. RIS-Metropolis Monte Carlo method indicated that insertion of GlcpA side chain induced a lowering effect of the calculated chain extension at low GlcpA:Xylp ratio (GlcpA:Xylp = 1:3). The chain, however, became extended when the ratio of GlcpA:Xylp above 2/3. It was also shown that the spatial extension of the polymer chains was dependent on the distribution of side chain: the random distribution demonstrated the most flexible structure compared to block and alternative distribution. The present studies provide a unique insight into the dependence of both side chain ratio and distribution on the stiffness and flexibility of various (GlcpA)Xylan molecules.

Study of the mechanism of formation of hyaluronan putty at pH 2.5: Part II—Theoretical analysis

A new method was developed for quantitative determination of the viscoelastical characteristics of hyaluronic acid (HA) putty (formed at pH 2.5) using a stress relaxation approach. A concept of entanglement network numbers (ENN) was applied to provide a quantitative measure for the strength of HA putty. Based on the new approach, the relationship between ENN and HA concentration was established. The new approach was successfully applied to evaluate the effect of temperature, urea concentration and pH on putty strength as well as estimate the effects of glucose, β1-3-linked D-glucuronic acid and β1-4 linked D-N-acetylglucosamine, on the ENN of HA solutions quantitatively. The ENN established in the current study can be extended to other non-cross linked hydrogels, i.e. they are formed by hydrogen bonds, ionic interactions or other non-covalent bonds.