Department of Infectious Diseases, St Jude Children's Research Hospital, Memphis, Tennessee, United States of America.
PLoS Pathog. 2023 May 31;19(5):e1011421. doi: 10.1371/journal.ppat.1011421. eCollection 2023 May.
Streptococcus pneumoniae is an opportunistic pathogen that colonizes the upper respiratory tract asymptomatically and, upon invasion, can lead to severe diseases including otitis media, sinusitis, meningitis, bacteremia, and pneumonia. One of the first lines of defense against pneumococcal invasive disease is inflammation, including the recruitment of neutrophils to the site of infection. The invasive pneumococcus can be cleared through the action of serine proteases generated by neutrophils. It is less clear how serine proteases impact non-invasive pneumococcal colonization, which is the key first step to invasion and transmission. One significant aspect of pneumococcal biology and adaptation in the respiratory tract is its natural competence, which is triggered by a small peptide CSP. In this study, we investigate if serine proteases are capable of degrading CSP and the impact this has on pneumococcal competence. We found that CSP has several potential sites for trypsin-like serine protease degradation and that there were preferential cleavage sites recognized by the proteases. Digestion of CSP with two different trypsin-like serine proteases dramatically reduced competence in a dose-dependent manner. Incubation of CSP with mouse lung homogenate also reduced recombination frequency of the pneumococcus. These ex vivo experiments suggested that serine proteases in the lower respiratory tract reduce pneumococcal competence. This was subsequently confirmed measuring in vivo recombination frequencies after induction of protease production via poly (I:C) stimulation and via co-infection with influenza A virus, which dramatically lowered recombination events. These data shed light on a new mechanism by which the host can modulate pneumococcal behavior and genetic exchange via direct degradation of the competence signaling peptide.
肺炎链球菌是一种机会致病菌，在上呼吸道无症状定植，一旦入侵，可导致严重疾病，包括中耳炎、鼻窦炎、脑膜炎、菌血症和肺炎。针对侵袭性肺炎球菌病的第一道防线之一是炎症，包括中性粒细胞向感染部位的募集。侵袭性肺炎球菌可以通过中性粒细胞产生的丝氨酸蛋白酶的作用被清除。丝氨酸蛋白酶如何影响非侵袭性肺炎球菌定植（这是侵袭和传播的关键第一步），其机制尚不清楚。肺炎链球菌在呼吸道中的一个重要生物学和适应特征是其天然感受态，这是由一种小肽 CSP 触发的。在这项研究中，我们研究了丝氨酸蛋白酶是否能够降解 CSP，以及这对肺炎球菌感受态的影响。我们发现 CSP 有几个潜在的胰蛋白酶样丝氨酸蛋白酶降解位点，并且有蛋白酶识别的优先切割位点。两种不同的胰蛋白酶样丝氨酸蛋白酶消化 CSP 可显著降低感受态，呈剂量依赖性。CSP 与小鼠肺匀浆孵育也降低了肺炎球菌的重组频率。这些离体实验表明，下呼吸道中的丝氨酸蛋白酶降低了肺炎球菌的感受态。通过 poly (I:C) 刺激和流感 A 病毒共感染诱导蛋白酶产生后测量体内重组频率，进一步证实了这一点，这显著降低了重组事件。这些数据揭示了宿主通过直接降解感受态信号肽来调节肺炎球菌行为和遗传交换的新机制。
