米曲霉（Aspergillus oryzae）果胶酸内切水解酶（PGA）在原核系统中重组表达

Expression of Endopolygalacturonase A of Aspergillus oryzae in Escherichia coli

摘要:

果胶酶具有广阔的商业用途，在食品工业上主要用于果汁和酒类的澄清、提高植物油的提取率、提高水果的硬度和植物纤维脱胶。米曲霉（Aspergillus oryzae）一直用于传统发酵食品的生产，自然条件下其果胶酶的产量较低。文献报道的果胶酶的重组表达成功的例子较少，且活性较低。通过RT-PCR 的方法，获得不含信号肽的果胶酸内切水解酶A(polygalacturonase A, PGA) 的cDNA，PGA cDNA 连入pET-28a (+)载体, 构建 pET-28a (+)-pga 质粒。pET-28a (+)-pga 转化Turner (DE3) placⅠ细胞，得到转化子pET-28a (+)-pga-Turner (DE3) placⅠ，首次实现了米曲霉PGA在大肠杆菌系统中过表达，进一步对PGA在大肠杆菌系统中表达的条件进行了研究。在37℃、220 r/min条件培养pET-28a (+)-pga-Turner (DE3) placⅠ细胞，OD₆₀₀至 0.8左右时，用500μmol/L isopropyl β-D-thiogalactogalactopyranoside (IPTG)进行诱导表达，在15℃和170r/min条件下继续培养24 h，表达效果最好，相对于每毫升培养基而言，产酶可达到70u/mL，是米曲霉自然条件产酶量的87.5倍，远优于文献报道的重组表达的PGA酶活

Abstract:

Pectinases are mainly used in the food industry to clarify fruit juices and wine, improve oil extraction, remove the peel from the citrus fruit, increase the firmness of some fruits and degum fibres. The filamentous fungus Aspergillus oryzae, used for the production of traditional fermented foods, only could produce less pectinases under general conditions. So far only a few of PGs expressed in yeast or E.coli were reported but they did not show higher activity. The cDNA of mature PGA (without signal peptide) was synthesized with specific primers from total RNA of Aspergillus oryzae by RT-PCR. PGA cDNA was ligated into pET-28a(+) expression vector, creating plasmid pET-28a(+)-pgA. The plasmid pET-28a(+)-pgA was transformed into E.coli Turner (DE3) placⅠcells to express PGA heterogeneously. For improving the efficiency of PGA expression in E.coli, the conditions for expression of the PGA in E.coli were optimized. E.coli Turner (DE3) placⅠcells with pET-28a(+)-pgA was first cultivated at 37℃，220r/min until OD_600nm reached about 0.8. Then, cultivation broth was added with 0.5 mmol/L IPTG and incubated at 15℃, 170r/min for other 24 h for induced-expression of PGA. Our data showed that the activity of recombinant expressed PGA could reach to 70u/mL medium, which is 87.5-fold of the activity of PGA produced in culture of A. oryzae and superior than known recombinant expression amount of PGA reported by other researchers.