Department of BioMolecular Sciences, University of Mississippi, Oxford, MS, USA.
Center for Immunology and Microbial Research, Department of Cell and Molecular Biology, University of Mississippi Medical Center, Jackson, MS, USA.
Int J Biol Macromol. 2023 May 31;238:124168. doi: 10.1016/j.ijbiomac.2023.124168. Epub 2023 Mar 22.
The structure of the sulfated galactan from the red alga Botryocladia occidentalis (BoSG) was originally proposed as a simple repeating disaccharide of alternating 4-linked α-galactopyranose (Galp) and 3-linked β-Galp units with variable sulfation pattern. Abundance was estimated only for the α-Galp units: one-third of 2,3-disulfation and one-third of 2-monosulfation. Here, we isolated again the same BoSG fractions from the anion-exchange chromatography, obtaining the same NMR profile of the first report. More careful NMR analysis led us to revise the structure. A more complex sulfation pattern was noted along with the occurrence of 4-linked α-3,6-anhydro-Galp (AnGalp) units. Interestingly, the more sulfated BoSG fraction showed slightly reduced in vitro anti-SARS-CoV-2 activities against both wild-type and delta variants, and significantly reduced anticoagulant activity. The BoSG fractions showed no cytotoxic effects. The reduction in both bioactivities is attributed to the presence of the AnGalp unit. Docking scores from computational simulations using BoSG disaccharide constructs on wild-type and delta S-proteins, and binding analysis through competitive SPR assays using blood (co)-factors (antithrombin, heparin cofactor II and thrombin) and four S-proteins (wild-type, delta, gamma, and omicron) strongly support the conclusion about the deleterious impact of the AnGalp unit.
红藻 Botryocladia occidentalis（BoSG）的硫酸化半乳聚糖的结构最初被提出为交替的 4 连接的α-半乳糖吡喃糖（Galp）和 3 连接的β-Galp 单元的简单重复二糖，具有可变的硫酸化模式。仅对α-Galp 单元进行了丰度估计：三分之一为 2,3-二硫酸化，三分之一为 2-单硫酸化。在这里，我们再次从阴离子交换层析中分离出相同的 BoSG 级分，得到与第一份报告相同的 NMR 图谱。更仔细的 NMR 分析使我们对结构进行了修正。注意到更复杂的硫酸化模式，同时还出现了 4 连接的α-3,6-脱水-Galp（AnGalp）单元。有趣的是，硫酸化程度较高的 BoSG 级分对野生型和 delta 变体的体外抗 SARS-CoV-2 活性均略有降低，抗凝血活性显著降低。BoSG 级分没有细胞毒性作用。两种生物活性的降低归因于 AnGalp 单元的存在。使用 BoSG 二糖构建体对野生型和 delta S 蛋白进行计算模拟的对接评分，以及通过使用血液（共）因子（抗凝血酶、肝素辅因子 II 和凝血酶）和四种 S 蛋白（野生型、delta、gamma 和 omicron）进行竞争性 SPR 分析的结合分析，强烈支持关于 AnGalp 单元的有害影响的结论。
