Hyaluronate tetrasaccharide-Cu(II) interaction: A NMR study

The coordination of Cu(II) to a hyaluronate tetrasaccharide (HAt) was investigated in aq. soln. by 13C and 1H relaxation measurements at two magnetic fields, 9 and 14 T. The HAt interaction with the metal ion was monitored following the nuclear paramagnetic relaxation enhancements R1p and R2p produced by the copper addn. The data anal. shows that the paramagnetic effect is differently experienced by the nuclei in different monosaccharide residues. A mol. model for the complex HAt-Cu(II) was built taking into account the exptl. data. The model shows the presence of two binding sites, both involving the carboxylate groups of the two glucuronic acid units. The first site, that best simulates the HA binding site, is located on the ligand core, while the second one is located on the terminal glucuronic acid residue. Both binding sites involve, in addn. to the carboxylate groups, the O4 oxygens of the glucuronic acid residues.