title: Identification of a heterologous cellulase and its N-terminus that can guide recombinant proteins out of Escherichia coli.
abstract: BACKGROUND
  The Gram-negative bacterium Escherichia coli has been widely used as a cell factory for the production of proteins and specialty chemicals because it is the best characterized host with many available expression and regulation systems. However, recombinant proteins produced in Escherichia coli are generally intracellular and often found in the form of inclusion bodies. Extracellular production of proteins is advantageous compared with intracellular production because extracellular proteins can be purified more easily and can avoid protease attack, which results in higher product quality. In this study, we found a catalytic domain of a cellulase (Cel-CD) and its N-terminus can be employed as carriers for extracellular production of recombinant proteins.
  
  
  RESULTS
  In this report, we identified the catalytic domain of a cellulase (Cel-CD) from Bacillus sp. that can be secreted into the medium from recombinant E. coli BL21 (DE3) in large quantities without its native signal peptide. By subcellular location analysis, we proved that the secretion was a two-step process and the N-terminal sequence of the full length Cel-CD played a crucial function in secretion. Both the Cel-CD and its N-terminal sequence can serve as carriers for efficient extracellular production of select target proteins.
  
  
  CONCLUSIONS
  Fusion of heterologous proteins with N20 from Cel-CD can carry the target proteins out of the cells with a concentration from 101 to 691 mg/L in flask cultivation. The extracellular recombinant proteins with a relative high purity. The results suggested that this system has a potential application in plant biomass conversion and industrial production of enzymes and therapeutic proteins.
authors.affiliation: State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, People's Republic of China. ga_o_df@126.com.
authors.forename: Dongfang
authors.initials: D
authors.lastname: Gao
authors.affiliation: State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, People's Republic of China. shengjun@sund.ku.dk.
authors.forename: Shengjun
authors.initials: S
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, People's Republic of China. lihaoran0124@163.com.
authors.forename: Haoran
authors.initials: H
authors.lastname: Li
authors.affiliation: State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, People's Republic of China. 745783960@qq.com.
authors.forename: Huili
authors.initials: H
authors.lastname: Yu
authors.affiliation: State Key Laboratory of Microbial Technology, Shandong University, Jinan, 250100, People's Republic of China. qiqingsheng@sdu.edu.cn.
authors.forename: Qingsheng
authors.initials: Q
authors.lastname: Qi
mesh_terms: D001407:Bacillus / Q000201:enzymology / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D020134:Catalytic Domain / Q000235:genetics; D002480:Cellulase / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D005110:Extracellular Space / Q000378:metabolism; D007218:Industrial Microbiology / Q000379:methods; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism*; D015203:Reproducibility of Results
chemical_list: D001426:Bacterial Proteins; D011993:Recombinant Fusion Proteins; D002480:Cellulase