Streptococcus pseudopneumoniae (SPpn) is a relatively new species closely related to S. pneumoniae (SPn) and S. mitis (SM) belonging to the Mitis group of the genus Streptococcus (MGS). Although genes encoding various pneumococcal virulence factors have been observed in the SPpn genome, the pathogenicity of SPpn against human, including the roles of virulence factor candidates, is still unclear. The present study focused on and characterized a candidate virulence factor previously reported in SPpn with deduced multiple functional domains, such as lipase domain, two lectin domains, and cholesterol‐dependent cytolysin‐related domain using various recombinant proteins. The gene was found not only in SPpn but also in the strains of SM and SPn. Moreover, the gene product was expressed in the gene‐positive strains as secreted and cell‐bound forms. The recombinant of gene product showed lipase activity and human cell‐binding activity depending on the function of lectin domain(s), but no hemolytic activity. Thus, based on the distribution of the gene within the MGS and its molecular function, the gene product was named mitilectin (MLC) and its contribution to the potential pathogenicity of the MLC‐producing strains was investigated. Consequently, the treatment with anti‐MLC antibody and the mlc gene‐knockout significantly reduced the human cell‐binding activity of MLC‐producing strains. Therefore, the multifunctional MLC was suggested to be important as an adhesion molecule in considering the potential pathogenicity of the MLC‐producing strains belonging to MGS, such as SPpn and SM.

中文翻译：

---

含有由减轻型链球菌产生的胆固醇依赖性溶细胞素基序的粘附分子的分子特征

链球菌pseudopneumoniae（SPpn）是密切相关的一个相对较新的物种肺炎链球菌（SPN）和缓症链球菌属于缓症链球菌组属（SM）链球菌(MGS)。尽管已在 SPpn 基因组中观察到编码各种肺炎球菌毒力因子的基因，但 SPpn 对人类的致病性，包括候选毒力因子的作用，仍不清楚。本研究重点关注并表征了先前在 SPpn 中报告的候选毒力因子，该毒力因子具有推导的多个功能域，例如脂肪酶域、两个凝集素域和使用各种重组蛋白的胆固醇依赖性溶细胞素相关域。该基因不仅存在于SPpn中，而且存在于SM和SPn菌株中。此外，基因产物在基因阳性菌株中以分泌和细胞结合形式表达。基因产物的重组显示出脂肪酶活性和人细胞结合活性，这取决于凝集素域的功能，但没有溶血活性。因此，根据基因在 MGS 中的分布及其分子功能，该基因产物被命名为丝裂素（MLC），并研究了其对产生 MLC 的菌株的潜在致病性的贡献。因此，用抗 MLC 抗体和mlc基因敲除显着降低了产生 MLC 的菌株的人类细胞结合活性。因此，在考虑属于 MGS 的产 MLC 菌株（如 SPpn 和 SM）的潜在致病性时，多功能 MLC 被认为是重要的粘附分子。