利用乳酸乳球菌AcmA表面展示β-1,3-1,4-葡聚糖酶

Functional cell surface display of endo-beta-1,3-1,4-glucanase in Lactococcus lactis using N-acetylmuraminidase as the anchoring motif

采用PCR扩增乳酸乳球菌(Lactococcus lactis)MB191菌株的全长肽聚糖水解酶基因acmA,通过C-末端融合构建了与绿色荧光基因gfp的融合基因acmA-gfp,再连接于表达载体pMG36k上后得到可组成型表达AcmA-GFP融合蛋白的重组质粒pMB137,然后将该质粒电转化导入到乳酸乳球菌AS1.2829中获得重组菌MB137。经SDS-PAGE检测,重组菌MB137可表达预期的分子量约74kD的蛋白质。Western blotting、细胞分级分离组分的荧光活性测定和特异GFP二抗标记的流式细胞仪检测证实GFP被成功锚定在重组菌细胞表面,被锚定蛋白约占总表达融合蛋白的35%。进一步通过从枯草芽胞杆菌BF7658基因组中扩增去信号肽序列的β-1,3-1,4葡聚糖酶基因gls,来取代pMB137中的gfp,得到携带融合基因acmA-gls的重组质粒pMB138,经导入到乳酸乳球菌AS1.2829后得到重组菌MB138,其全细胞β-1,3-1,4-葡聚糖水解酶的活性约为12U/mL菌液,明显高于对照菌株。

In this report, we utilized N-Acetylmuraminidase （AcmA） to develop a whole-cell catalyst of endo-beta-1, 3-1, 4- glucanase in Lactococcus lactis. The PCR-amplified full-length acmA gene from L. lactis MB191 was fused with the green fluorescent gene （gfp）, followed by ligating the chimeric acmA-gfp into the Escherichia coli-L, lactis shuttle expression vector pMG36k, yielding the recombinant plasmid pMB137. SDS-PAGE analysis showed that the constitutive expression of AcmA-GFP fusion protein in the L. lactis AS1.2829 construct harboring pMB137 （named MBI37）, with the predicted Mr of 74 kD. Western blotting, GFP specific fluorescence intensity assays and flow cytometry analysis confirmed that AcmA-GFP was immobilized on the outer membrane, which constituted approx. 35% of the total intracellular fusion protein. Furthermore, acmA was fused with a PCR-amplified encoding fragment of the endo-beta-1, 3-1, 4-glucanase gene （gls） from Bacillus sublitis BF7658, resulting in the recombinant plasmid pMB138. By transferring pMB138 into L. lactis AS1.2829, the derived L. lactis MB138 expressing the AcmA-GLS fusion enzyme exhibited a distinct whole-cell glucanase activity （by 12 U/mL） compared to the control strain, indicating AcmA had served as a functional anchoring motif to immobilize the heterologous enzyme on the cell surface of L. lactis.