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Profiling glycosaminoglycan complex substitution patterns by two-dimensional NMR spectroscopy

Biological and pharmacological interactions of heparin and structurally-related glycosaminoglycans (GAGs) such as heparan sulfate (HS) involve complex sequences of variously sulfated uronic acid and aminosugar residues. Due to their structural microheterogeneity, these sequences are usually characterized in statistical terms, by HPLC analysis of fragments obtained by enzymatic or chemical degradation. NMR spectroscopy is also used for structural characterization of GAGs.

However, monodimensional NMR analysis of complex GAGs is often limited by severe signal overlap that does not permit reliable quantitative measurements.

With proper choice of the analytical signals, the higher resolution achieved with two dimensional (2D) NMR methods could be exploited also for quantitative applications. Heteronuclear single quantum coherence (HSQC) spectroscopy has been evaluated to determine variously substituted monosaccharide components of HS and of HS mimics obtained by chemical modification of the common biosynthetic precursor of heparin and HS E. Coli K5 polysaccharide.

Heparin was used as a model for assessing the influence of 1H-13C magnetic couplings on “volumes” of the corresponding signals. For major signals, the HSQC approach permitted to quantify additional structural features both in heparin and in a typical HS. The method was applied to profile the susbstitution patterns of K5 polysaccharide derivatives involving different degrees of N,O-sulfation and N-acetylation, including O-sulfated heparosans bearing free amino groups.
There is an increasing interest in oversulfated oligo and polysaccharides for medical application (i.e. oncology, virology). We can foresee a wide application of this approaches in characterization of these complex molecules.

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Reported by

Istituto di Ricerche Chimiche e Biochimiche G. Ronzoni
Via G. Colombo 81
20133 Milan
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