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Nat Biotechnol. 2005 Apr;23(4):475-81. Epub 2005 Apr 3.

Extracellular secretion of polypeptides using a modified Escherichia coli flagellar secretion apparatus.

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General Microbiology, Faculty of Biosciences, P.O. Box 56, FIN-00014 University of Helsinki, Helsinki, Finland.


We developed a modified flagellar type III secretion apparatus to secrete heterologous polypeptides into the growth medium of Escherichia coli. The secretion was facilitated by fusing the 173-bp untranslated DNA fragment upstream of the gene fliC (encoding flagellin) as well as a transcriptional terminator from fliC, into the gene encoding the polypeptide of interest. The polypeptides secreted into the growth medium at concentrations ranging from 1 to 15 mg/l were from Campylobacter jejuni (262 residues in length), Streptococcus pneumoniae (434 residues), Staphylococcus aureus (115 residues), and N-terminal FliC hybrid proteins, for example, the eukaryotic green fluorescent protein (238 residues). The expressed proteins represented >50% of total secreted protein. Previously reported protein yields from extracellular secretion of foreign proteins in E. coli have been low, approximately 100 microg/l. The strengths of our method are the concentration and purity of the secreted proteins and its versatility with regard to the proteins' length and origin.

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