毛蕊花糖苷抑制2型猪链球菌的溶血素蛋白活性而降低其小鼠致病性

Verbascoside lowers Streptococcus suis serotype 2 pathogenicity in mice by inhibiting hemolytic activity of suilysin

为了探究天然化合物毛蕊花糖苷(verbascoside, VBS)对2型猪链球菌(Streptococcus suis serotype 2, SS2)致病性的作用,本研究通过测定最低抑菌浓度、绘制细菌生长曲线及红细胞溶血试验,发现低浓度下的毛蕊花糖苷不影响猪链球菌的正常生长,但对其溶血活性有显著抑制作用;免疫印迹试验表明,毛蕊花糖苷不影响2型猪链球菌分泌溶血素蛋白(suilysin, SLY);通过分子对接预测毛蕊花糖苷可与SLY的2个氨基酸残基(SER-388、GLN-441)形成3条氢键结合从而使毛蕊花糖苷嵌入SLY蛋白的第4结构域,同时体外溶血活性试验进一步证实毛蕊花糖苷可直接抑制SLY介导的溶血活性;最后,小鼠体内试验结果表明,毛蕊花糖苷可明显提高2型猪链球菌感染小鼠的存活率。综上,毛蕊花糖苷在不影响2型猪链球菌生长活性的情况下,可通过抑制溶血素活性来降低2型猪链球菌对小鼠的致病性。

The aim of this study is to explore the effect of verbascoside(VBS), a natural compound, on the pathogenicity of Streptococcus suis serotype 2(SS2). By determining the minimum inhibitory concentration(MIC), growth curve of SS2 and hemolysis activity of erythrocytes, is was found that the low concentration of VBS significantly inhibited the hemolytic activity of SS2 without interfering with its growth. Western blotting showed that VBS had no influence on the expression of suilysin(SLY) in SS2. It was predicted by molecular docking that VBS could be embedded into the domain 4 of SLY, which was through the formation of three hydrogen bonds between VBS and two residues(SER-388, GLN-441) of SLY. And it was further confirmed that VBS directly inhibited the hemolytic activity of SLY in vitro. Moreover, VBS significantly increased the survival rate of mice infected with SS2 in vivo. In conclusion, without affecting the growth of SS2, VBS can inhibit the hemolytic activity of SLY to reduce the pathogenicity of SS2 in mice.