Pilus formation and protein secretion by the same machinery in Escherichiacoli

The secreton (type II secretion) and type IV pilus biogenesis branches of t he general secretory pathway id Gram-negative bacteria share many features that suggest a common evolutionary origin. Five components of the secreton, the pseudopilins, are similar to subunits of type IV pill, Here, we report that when the 15 genes encoding the pullulanase secreton of Klebsiella oxy toca were expressed on a high copy number plasmid in Escherichia coli, one pseudopilin, PulG, was assembled into pilus-like bundles. Assembly of the ' secreton pilus' required most but not all of the secreton components that a re essential for pullulanase secretion, including some with no known homolo gues in type IV piliation machineries. Two other pseudopilins, pullulanase and two outer membrane-associated secreton components were not associated w ith pill. Thus, PulG is probably the major component of the pilus, Expressi on of a type IV pilin gene, the E. coli K-12 gene ppdD, led to secreton-dep endent incorporation of PpdD pilin into pill without diminishing pullulanas e secretion. This is the first demonstration that pseudopilins can be assem bled into pilus-like structures.