Data_Sheet_2_The S Protein of Group B Streptococcus Is a Critical Virulence Determinant That Impacts the Cell Surface Virulome.xlsx

Group B Streptococcus (GBS, S. agalactiae) is a human commensal and occasional pathogen that remains a leading cause of neonatal sepsis and meningitis with increasing disease burden in adult populations. Although programs for universal screening in pregnancy to guide intrapartum prophylaxis have reduced GBS invasive disease burden resulting from mother-to-newborn transfer during birth, better knowledge of disease mechanisms may elucidate new strategies to reduce antibiotic exposure. In our efforts to expand the knowledge base required for targeted anti-virulence therapies, we identified a GBS homolog for a recently identified virulence determinant of group A Streptococcus, S protein, and evaluated its role in GBS pathogenesis. A GBS S protein deletion mutant, Δess, showed altered cell-surface properties compared to the WT parent strain, including defective retention of its surface polysaccharide. Quantitative proteome analysis of enzymatically shaved surface epitopes of the GBS Δess mutant revealed a dysregulated cell surface virulome, with reduced abundance of several protein and glycoprotein components. The Δess mutant showed markedly attenuated virulence in a murine model of GBS systemic infection, with increased proteasome activity detected in the spleens of animals infected with the Δess mutant. These results expand the key roles S protein plays in streptococcal pathogenesis and introduces a new GBS virulence determinant and potential target for therapy development.

B群链球菌（Group B Streptococcus, GBS，又称无乳链球菌Streptococcus agalactiae, S. agalactiae）是人体共生的条件致病菌，目前仍是新生儿败血症与脑膜炎的主要致病菌，且成人感染群体的疾病负担持续攀升。尽管针对孕妇的通用筛查以指导产时预防的相关方案，已有效降低了分娩期母婴垂直传播引发的GBS侵袭性疾病负担，但对疾病致病机制的深入解析，或可阐明减少抗生素暴露的全新治疗策略。在拓展靶向抗毒力治疗所需知识库的研究工作中，我们鉴定出了新近发现的A群链球菌毒力决定因子——S蛋白的GBS同源蛋白，并评估了其在GBS致病过程中的功能。研究发现，GBS的ess基因缺失突变株（Δess mutant）与野生型亲本菌株相比，细胞表面特性发生显著改变，其中包括表面多糖保留功能缺陷。对该Δess突变株的酶解剥离表面表位开展定量蛋白质组学分析后，我们观察到其细胞表面毒力组存在失调现象，多种蛋白质与糖蛋白组分的丰度均显著降低。该Δess突变株在GBS全身感染小鼠模型中表现出明显减弱的毒力，且感染该突变株的小鼠脾脏内检测到了升高的蛋白酶体活性。上述研究结果拓展了我们对S蛋白在链球菌致病过程中关键作用的认知，同时鉴定出一种全新的GBS毒力决定因子，为抗GBS感染治疗的开发提供了潜在靶点。