Flanking N- and C-terminal domains of PrsA in Streptococcus suis type 2 are crucial for inducing cell death independent of TLR2 recognition

ABSTRACT

Streptococcus suis type 2 (SS2), a major emerging/re-emerging zoonotic pathogen found in humans and pigs, can cause severe clinical infections, and pose public health issues. Our previous studies recognized peptidyl-prolyl isomerase (PrsA) as a critical virulence factor promoting SS2 pathogenicity. PrsA contributed to cell death and operated as a pro-inflammatory effector. However, the molecular pathways through which PrsA contributes to cell death are poorly understood. Here in this study, we prepared the recombinant PrsA protein and found that pyroptosis and necroptosis were involved in cell death stimulated by PrsA. Specific pyroptosis and necroptosis signalling inhibitors could significantly alleviate the fatal effect. Cleaved caspase-1 and IL-1β in pyroptosis with phosphorylated MLKL proteins in necroptosis pathways, respectively, were activated after PrsA stimulation. Truncated protein fragments of enzymatic PPIase domain (PPI), N-terminal (NP), and C-terminal (PC) domains fused with PPIase, were expressed and purified. PrsA flanking N- or C-terminal but not enzymatic PPIase domain was found to be critical for PrsA function in inducing cell death and inflammation. Additionally, PrsA protein could be anchored on the cell surface to interact with host cells. However, Toll-like receptor 2 (TLR2) was not implicated in cell death and recognition of PrsA. PAMPs of PrsA could not promote TLR2 activation, and no rescued phenotypes of death were shown in cells blocking of TLR2 receptor or signal-transducing adaptor of MyD88. Overall, these data, for the first time, advanced our perspective on PrsA function and elucidated that PrsA-induced cell death requires its flanking N- or C-terminal domain but is dispensable for recognizing TLR2. Further efforts are still needed to explore the precise molecular mechanisms of PrsA-inducing cell death and, therefore, contribution to SS2 pathogenicity.

KEYWORDS:

• Streptococcus suis type 2
• PrsA
• pyroptosis
• necroptosis
• TLR2

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data Availability statement

The authors confirmed that all data supporting the findings of this study are available within the article.

Authors’ Contribution

XWJ and MY: Conceptualization, methodology, formal analysis, writing – review and editing; GJY and LXZ: formal analysis, data curation, writing – review and editing; AS, DBZ and LHZ: formal analysis and data curation. All authors have read and agreed to the published version of the manuscript.

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work is funded by the National Natural Science Foundation of China (No. 32060791) and Jiangxi Provincial Natural Science Foundation (20202BABL215025).