NMR spectroscopic detection of interactions between a HIV protein sequence and a highly anti-HIV active curdlan sulfate

A new method is found for the detection of interactions between a highly anti-HIV (human immunodeficiency virus) active curdlan sulfate (CS) and a HIV peptide with the aid of NMR spectroscopy. To elucidate the action mechanism of the anti-HIV activity in curdlan sulfate, a partial peptide sequence in an envelope glycoprotein gp120 was synthesized. The sequence consists of a dimer (D518) of the sequence from no. 506 to 518, which is one of putative reaction sites for the sulfated polysaccharide. This was used to examine its interactions with CS. When CS and D518 were mixed in appropriate molar ratios, gel-like materials were formed. H-1 NMR spectra of the gel-like material revealed the formation of interpolymeric ionic interactions between a negatively charged CS and a positively charged D518. At the molar ratio [CS]/[D518] of 0.27, 100% gel formation was observed. Effects of molar ratio, pH, and temperature on the gel formation, that is, the degree of interaction, were also studied. In addition, although for a V3 region peptide sequence, i.e., nos. 309 to 331, the same method was applied, the mixing of CS with the V3 peptide did not provide gels, but yielded precipitates which afforded no structural information by solution NMR spectroscopy.