Glycosaminoglycans (GAGs) are long polysaccharide chains that exist on cell surfaces. Their high negative charge density enables them to interact electrostatically with cationic cell-penetrating compounds (CPCs) used in gene and drug delivery. Previous studies using isothermal titration calorimetry (ITC) have measured binding energies occurring between the GAG heparin and common CPC polyethylenimine (PEI); however, the binding locations remain unknown. Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for identification of binding sites and determining binding constants, structural dynamics, and reaction rates. Rates of chemical exchange influence peak character as demonstrated by chelation studies of ethylenediaminetetraacetic acid (EDTA) with metal cations. Slow tumbling times, conformational inhomogeneities and chemical shift anisotropies of the GAGs significantly broadened their NMR spectra, so heparin disaccharide I-S and chondroitin disaccharide Ddi-4S were utilized as model compounds. Carbohydrate stereoisomers produce complex 1H NMR spectra; therefore, example spectra of a and b anomers of D-glucopyranose and 1H-1H COSY aided the peak assignments of the GAGs. Chemical shift changes were monitored to identify the specific binding locations in the titration of the heparin disaccharide with an oligomer of polyethylenimine, (triethylenetetraamine).

NMR binding studies of glycosaminoglycans and cell-penetrating compounds

251st National Meeting (2016)

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