The Use of a Flagellar Export Signal for the Secretion of Recombinant Proteins in Salmonella

The flagellum-specific export system is a specialized type III export machinery, which exports external flagellar proteins through the central channel of the flagellar filament. A number of evidence indicates that short segments within the disordered N-terminal region of flagellar axial proteins are recognized by the flagellum-specific export apparatus. Recently, we have demonstrated that the 26–47 segment of Salmonella typhimurium flagellin is capable of mediating flagellar export. N-terminal flagellin segments containing the export signal combined with a hexahistidine tag can be attached to heterologous proteins (preferentially in the size range of 9–40 kDa) facilitating their secreted expression and easy purification from the medium. Certain over-expressed proteins that are easily degraded within the cells are found intact in the medium implying a potential application of this expression system for proteins of high proteolytic susceptibility.