Fimbrial biogenesis genes of Pseudomonas aeruginosa: pilW and pilX increase the similarity of type 4 fimbriae to the GSP protein‐secretion systems and pilY1 encodes a gonococcal PilC homologue

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Abstract
Summary: Type 4 fimbriae of Pseudomonas aeruginosa are surface filaments involved in host colonization. They mediate both attachment to host epithelial cells and flagella‐independent twitching motility. Four additional genes, pilW, pilX, pilY1 and pilY2, are located on Spel fragment E in the 5 kb intergenic region between the previously characterized genes pilV and pilE, which encode prepilin‐like proteins involved in type 4 fimbrial biogenesis. The phenotypes of a transposon insertion and other mutations constructed by allelic exchange show that these genes are involved in the assembly of type 4 fimbriae. The PilW and PilX proteins are membrane located, possess the hydrophobic N‐terminus characteristic of prepilin‐like proteins, and appear to belong to the GspJ and GspK group of proteins that are required for protein secretion in a wide range of Gram‐negative bacteria. These findings increase the similarities between the fimbrial biogenesis and the Gsp‐based protein‐secretion super‐systems. PilY1 is a large protein with C‐terminal homology to the PilC2 protein of Neisseria gonorrhoeae, thought to be a fimbrial tip‐associated adhesin, and which, like PilY1, is involved in fimbrial assembly. PilY1 appears to be located in both the membrane and the external fimbrial fractions. PilY2 is a small protein that appears to play a subtle role In fimbrial biogenesis and represents a new class of protein.