NMR Spectroscopic Detection of Interactions between a HIV Protein Sequence and a Highly Anti-HIV Active Curdlan Sulfate

Preparation of Single-Helical Curdlan Hydrogel and Its Activation with Coagulation Factor G

β-1,3-glucans are a kind of natural polysaccharide with immunomodulatory, antitumor, and anti-inflammatory properties. Curdlan, as the simplest linear β-1,3-glucan, possesses a variety of biological activities and thermogelation properties. However, due to the complexity and variability of the conformations of curdlan, the exact structure-activity relationship remains unclear. We prepare a chemically crosslinked curdlan hydrogel with the unique single-helical skeleton (named S gel) in 0.4 wt% NaOH at 40 °C, confirmed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). X-ray diffractometry (XRD) data show that S gel maintains the single-helical crystal structure, and the degree of crystallinity of the S gel is ~24%, which is slightly lower than that of the raw powder (~31%). Scanning electron microscopy (SEM) reveals that S gel has a continuous network structure, with large pores measuring 50-200 μm, which is consistent with its high swelling property. Using the 13C high-resolution magic angle spinning nuclear magnetic resonance (HRMAS NMR) method, we determine that most of the single-helical skeleton carbon signals in the swollen S gel are visible, suggesting that the single-helical skeleton of S gel exhibits fascinating mobility at room temperature. Finally, we reveal that the binding of S gel to coagulation Factor G from tachypleus amebocyte lysate increases and saturates at 20 μL tachypleus amebocyte lysate per mg of S gel. Our prepared S gel can avoid the transformation of curdlan conformations and retain the bioactivity of binding to coagulation Factor G, making it a valuable material for use in the food industry and the pharmaceutical field. This work deepens the understanding of the relationship between the single-helical structure and the activity of curdlan, promoting the development and application of β-1,3-glucans.

Role of a long-chain alkyl group in sulfated alkyl oligosaccharides with high anti-HIV activity revealed by SPR and DLS

Although a long-chain alkyl group in sulfated oligosaccharides can enhance the anti-HIV activity, the exact mechanism is unclear. To elucidate the role of the long-chain alkyl group, its interaction with a liposome (100 nm) as a HIV model was investigated by surface plasmon resonance and dynamic light scattering. The newly synthesized sulfated 1-(decadecyl-1, 2, 3-triazole)-1-deoxy- maltoheptaoside bearing the long-chain alkyl group was found to interact with the liposome. The particle size increased and the ζ potential was negative, indicating that the sulfated alkyl maltoheptaoside was attached to the liposome by the long-chain alkyl group and the fixed sulfated maltoheptaoside moiety was covered on the liposome. Thus, the long-chain alkyl group penetrates and is fixed into the lipid bilayer of HIV and the sulfated maltoheptaose moiety with negatively charged sulfate groups was electrostatically interacted with HIV gp120 molecule with positively charged amino acids to achieve the inhibition of HIV infection.

Interaction between sulfated 3-O-octadecyl-α-(1→6)-d-glucan and liposomes analyzed by surface plasmon resonance

To elucidate the role of long alkyl group in sulfated poly- and oligosaccharides on anti-HIV activity, the interaction between sulfated 3-O-octadecyl-(1→6)-α-d-glucopyranan with potent anti-HIV activity and liposomes with diameters of 58 ± 20 nm and 107 ± 28 nm as models of HIV were investigated. SPR measurements of sulfated 3-O-octadecyl-(1→6)-α-d-glucopyranans bearing 2.8 mol% of the octadecyl group and the liposome (diameter = 58 ± 20.0 nm and ζ=0 mV) resulted in an apparent association- k_a = 6 × 10⁵ 1/M, a dissociation-rate k_d = 4 × 10^-4 1/s, and a dissociation constants K_D = 8 × 10^-10 M. The particle size of the sulfated 3-O-octadecyl-(1→6)-α-d-glucopyranan (67 ± 14 nm) measured by DLS increased to 104 ± 25 nm, whereas the ζ potential (-29 mV) was unchanged (-33 mV). For dextran sulfate without an alkyl group, no interaction was observed. These results suggest that the long octadecyl group penetrated into the liposome and sulfated glucopyranan was covered on the liposome to increase the anti-HIV activity. The 107 nm liposome exhibited similar results.

Analysis of interaction between sulfated polysaccharides and HIV oligopeptides by surface plasmon resonance

This study aims to quantitatively investigate the interaction between sulfated polysaccharides with potent anti-HIV activity, dextran and curdlan sulfates with negatively charged sulfate groups, and poly-L-lysine as a model protein and oligopeptides from a HIV surface glycoprotein gp120 with positively charged amino acids using surface plasmon resonance (SPR) and dynamic light scattering (DLS) to elucidate the anti-HIV mechanism of sulfated polysaccharides. The apparent association- (k_a) and dissociation rate (k_d) constants of dextran and curdlan sulfates against poly-L-lysine were k_a = 6.92 × 10⁴-2.17 × 10⁶ 1/Ms and k_d = 4.29 × 10^-5-2.22 × 10^-4 1/s; these kinetic constants were dependent on the molecular weights and degree of sulfation of sulfated polysaccharides. For interaction, the three oligopeptides from the HIV gp120 were peptide A ²⁹⁷TRPNNNTRKRIRIQRGPGRA³¹⁶ with several lysine (K) and arginine (R) in the V3 loop region, peptide B ⁴⁹³PLGVAPTKAKRRVVQREKR⁵¹¹ with several K and R in the C-terminus region, and oligopeptide C ³⁶²KQSSGGDPEIVTHSFNCGG³⁸⁰ with few basic amino acids in the CD4 binding domain. Sulfated polysaccharides exhibited strong interaction against oligopeptides A and B, (k_a = 5.48 × 10⁴-2.96 × 10⁶ 1/Ms. and k_d = 1.74 × 10^-4-6.24 × 10^-3 1/s), no interaction was noted against oligopeptide C. Moreover, the particle size and zeta potential by DLS indicated the interaction between sulfated polysaccharides and oligopeptides A and B, suggesting the anti-HIV mechanism of sulfated polysaccharides to be the electrostatic interaction of negatively charged sulfated polysaccharides and HIV at the positively charged amino acid regions.