Streptococcus thermophilus is an important food starter and receiving more attention to serve as cell factories for production of high-valued metabolites. However, the low yields of intracellular or extracellular expression of biotechnological and biomedical proteins limit its practical applications. Here, an enolase EnoM was identified from S. thermophilus CGMCC7.179 with about 94% identities to the surface-located enolases from other Streptococcus spp. strains. The EnoM was used as an anchor to achieve surface display in S. thermophilus using GFP as a reporter. After respectively mixing the GFP-EnoM fusion protein or GFP with S. thermophilus cells in vitro, the relative fluorescence units (RFU) of the S. thermophilus cells with GFP-EnoM was 80-folds higher than that with purified GFP. The sharp decrease in the RFU of sodium dodecyl sulfate (SDS) pretreated cells compared to those of non-pretreated cells demonstrated that the membrane proteins were the binding ligand of EnoM. Furthermore, an engineered β-galactosidase (β-Gal) was also successfully displayed on the cell surface of S. thermophilus CGMCC7.179 and the relative activity of the immobilized β-Gal remained up to 64% after reused 8 times. Finally, we also demonstrated that EnoM could be used as an anchor for surface display in L. casei, L. bulgaricus, L. lactis and Leuconostoc lactis. To our knowledge, EnoM from S. thermophilus was firstly identified as an anchor and successfully achieved surface display in LAB. The EnoM-based surface display system provided a novel strategy for the enzyme immobilization.

中文翻译：

---

嗜热链球菌表面展示的月光蛋白烯醇化酶的鉴定和表征。

嗜热链球菌是重要的食物起步剂，并作为生产高价值代谢产物的细胞工厂而受到更多关注。但是，生物技术和生物医学蛋白质在细胞内或细胞外表达的低产量限制了其实际应用。在这里，从嗜热链球菌CGMCC7.179中鉴定出一种烯醇酶EnoM，其与来自其他链球菌属的表面定位的烯醇酶具有约94％的同一性。株。EnoM用作锚点，以绿色荧光蛋白为报告基因在嗜热链球菌中实现表面展示。在将GFP-EnoM融合蛋白或GFP分别与嗜热链球菌细胞混合后，带有GFP-EnoM的嗜热链球菌细胞的相对荧光单位（RFU）比纯化的GFP高80倍。与未预处理的细胞相比，十二烷基硫酸钠（SDS）预处理的细胞的RFU急剧下降表明，膜蛋白是EnoM的结合配体。此外，工程β-半乳糖苷酶（β-Gal）也成功展示在嗜热链球菌CGMCC7.179的细胞表面上，固定化的β-Gal的相对活性在重复使用8次后仍保持高达64％。最后，我们还证明了EnoM可以用作干酪乳杆菌，保加利亚乳杆菌，乳酸乳球菌和乳酸乳球菌表面展示的锚。据我们所知，嗜热链球菌的EnoM首先被鉴定为锚，并在LAB中成功实现了表面展示。基于EnoM的表面展示系统为酶的固定化提供了新的策略。