Secreted proteins are one of the direct molecular mechanisms by which microbiota influence the host, thus constituting a promising field for drug discovery. Here, through bioinformatics-guided screening of the secretome of clinically established probiotics from Lactobacillus, we identify an uncharacterized secreted protein (named LPH here) that is shared by most of these probiotic strains (8/10) and demonstrate that it protects female mice from colitis in multiple models. Functional studies show that LPH is a bi-functional peptidoglycan hydrolase with both N-Acetyl-β-D-muramidase and DL-endopeptidase activities that can generate muramyl dipeptide (MDP), a NOD2 ligand. Different active site mutants of LPH in combination with Nod2 knockout female mice confirm that LPH exerts anti-colitis effects through MDP-NOD2 signaling. Furthermore, we validate that LPH can also exert protective effects on inflammation-associated colorectal cancer in female mice. Our study reports a probiotic enzyme that enhances NOD2 signaling in vivo in female mice and describes a molecular mechanism that may contribute to the effects of traditional Lactobacillus probiotics.

分泌蛋白是微生物群影响宿主的直接分子机制之一，因此构成了药物发现的一个有前景的领域。在这里，通过生物信息学指导筛选临床建立的乳杆菌益生菌的分泌蛋白组，我们鉴定了大多数这些益生菌菌株 (8/10) 共有的一种未表征的分泌蛋白（此处称为 LPH），并证明它可以保护雌性小鼠免受感染。多种模型中的结肠炎。功能研究表明，LPH 是一种双功能肽聚糖水解酶，具有 N-乙酰基-β-D-胞壁质酶和 DL-内肽酶活性，可生成胞壁酰二肽 (MDP)（一种 NOD2 配体）。 LPH 的不同活性位点突变体与Nod2敲除雌性小鼠相结合，证实 LPH 通过 MDP-NOD2 信号传导发挥抗结肠炎作用。此外，我们验证 LPH 还可以对雌性小鼠炎症相关的结直肠癌发挥保护作用。我们的研究报道了一种益生菌酶，它可以增强雌性小鼠体内 NOD2 信号传导，并描述了可能有助于传统乳酸菌益生菌作用的分子机制。