Department of Immunology and Infectious Diseases, Montana State University, Bozeman, Montana, USA.
Infect Immun. 2013 Sep;81(9):3128-38. doi: 10.1128/IAI.00398-13. Epub 2013 Jun 17.
Human pathogen group A streptococcus (GAS) has developed mechanisms to subvert innate immunity. We recently reported that the secreted esterase produced by serotype M1 GAS (SsE(M1)) reduces neutrophil recruitment by targeting platelet-activating factor (PAF). SsE(M1) and SsE produced by serotype M28 GAS (SsE(M28)) have a 37% sequence difference. This study aims at determining whether SsE(M28) is also a PAF acetylhydrolase and participates in innate immune evasion. We also examined whether SsE evolved to target PAF by characterizing the PAF acetylhydrolase (PAF-AH) activity and substrate specificity of SsE(M1), SsE(M28), SeE, the SsE homologue in Streptococcus equi, and human plasma PAF-AH (hpPAF-AH). PAF incubated with SsE(M28) or SeE was converted into lyso-PAF. SsE(M1) and SsE(M28) had kcat values of 373 s(-1) and 467 s(-1), respectively, that were ≥ 30-fold greater than that of hpPAF-AH (12 s(-1)). The comparison of SsE(M1), SsE(M28), and hpPAF-AH in kcat and Km in hydrolyzing triglycerides, acetyl esters, and PAF indicates that the SsE proteins are more potent hydrolases against PAF and have high affinity for PAF. SsE(M28) possesses much lower esterase activities against triglycerides and other esters than SsE(M1) but have similar potency with SsE(M1) in PAF hydrolysis. Deletion of sse(M28) in a covS deletion mutant of GAS increased neutrophil recruitment and reduced skin infection, whereas in trans expression of SsE(M28) in GAS reduced neutrophil infiltration and increased skin invasion in subcutaneous infection of mice. These results suggest that the SsE proteins evolved to target PAF for enhancing innate immune evasion and skin invasion.
人类病原体 A 群链球菌（GAS）已经开发出了多种机制来颠覆先天免疫。我们最近报道称，M1 血清型 GAS 产生的分泌型酯酶（SsE(M1)）通过靶向血小板激活因子（PAF）来减少中性粒细胞的募集。M28 血清型 GAS 产生的 SsE(M28)和 SsE 之间有 37%的序列差异。本研究旨在确定 M28 型 SsE 是否也是一种 PAF 乙酰水解酶，并参与先天免疫逃避。我们还通过研究 M1 型 SsE、M28 型 SsE、SeE、马链球菌 SsE 同源物以及人血浆 PAF-乙酰水解酶（hpPAF-AH）的 PAF 乙酰水解酶（PAF-AH）活性和底物特异性，来研究 SsE 是否通过进化来靶向 PAF。与 SsE(M28)或 SeE 孵育的 PAF 被转化为溶血 PAF。SsE(M1)和 SsE(M28)的 kcat 值分别为 373 s(-1)和 467 s(-1)，分别是 hpPAF-AH（12 s(-1)）的 30 多倍。对 SsE(M1)、SsE(M28)和 hpPAF-AH 在水解三酰基甘油、乙酰酯和 PAF 中的 kcat 和 Km 的比较表明，SsE 蛋白是更有效的 PAF 水解酶，对 PAF 具有高亲和力。与 SsE(M1)相比，SsE(M28)对三酰基甘油和其他酯的酯酶活性要低得多，但在 PAF 水解方面与 SsE(M1)具有相同的效力。GAS 的 covS 缺失突变体中 sse(M28)的缺失增加了中性粒细胞的募集并减少了皮肤感染，而 GAS 中转基因表达 SsE(M28)则减少了中性粒细胞浸润并增加了皮下感染小鼠的皮肤入侵。这些结果表明，SsE 蛋白进化为靶向 PAF，以增强先天免疫逃避和皮肤入侵。
