Common components in the assembly of type 4 fimbriae, DNA transfer systems, filamentous phage and protein‐secretion apparatus: a general system for the formation of surface‐associated protein complexes

Abstract

Summary The Pseudomonas aeruginosa genes pilB‐D and pilQ are necessary for the assembly of type 4 fimbriae. Homologues of these genes and of the subunit (pilin) gene have been described in various different bacterial species, but not always in association with type 4 fimbrial biosynthesis and function. Pil‐like proteins are also involved in protein secretion, DNA transfer by conjugation and transformation, and morphogenesis of filamentous bacteriophages. It seems likely that the Pil homologues function in the processing and export of proteins resembling type 4 fimbrial sub‐units, and in their organization into fimbrial‐like structures. These may either be true type 4 fimbriae, or components of protein complexes which act in the transport of macromolecules (DNA or protein) into or out of the cell. Some PilB‐like and PilQ‐like proteins are apparently also involved in the assembly of non‐type 4 polymeric structures (filamentous phage virions and conjugative pili). The diverse studies summarized in this review are providing insight into an extensive infrastructural system which appears to be utilized in the formation of a variety of cell surface‐associated complexes.

Identification of the Vibrio cholerae type 4 prepilin peptidase required for cholera toxin secretion and pilus formation

“…Type 4 prepilins are divided into two distinct subtypes, type 4a and type 4b, based on various conserved sequence homologies (Hobbs and Mattick, 1993). The Msh prepilins and the Eps prepilin-like proteins belong to the type 4a category.…”

BfpU, a soluble protein essential for type IV pilus biogenesis in enteropathogenic Escherichia coli

“…Thus, no mutations of type IV pilus biogenesis genes have resulted in the accumulation of free pilin in the periplasmic space and no periplasmic chaperones have been described. This has led some Soluble protein and type IV pilus biogenesis investigators to propose models for type IV pilus biogenesis that include no periplasmic phase of export, but instead envisage a structure that spans the inner and outer membranes (Fussenegger et al, 1997 ;Iredell & Manning, 1994 ;Hobbs & Mattick, 1993). Recently, the use of conditional double-knockout mutants has allowed the dissection of type IV pilus formation into three different phases -pilin processing, pilus formation and pilus extrusion (Wolfgang et al, 1998(Wolfgang et al, , 2000.…”

“…Another striking feature of type IV pilus biogenesis systems is their similarity to type II secretion systems (Pugsley, 1993 ;Hobbs & Mattick, 1993 ;Russel, 1998 ;Nouwen et al, 1999Nouwen et al, , 2000. Type II secretion systems are responsible for the export of a variety of extracellular toxins and enzymes through the outer membrane.…”

The Platform Protein Is Essential for Type IV Pilus Biogenesis

“…T4P assembly systems are evolutionarily and functionally related to the type II secretion (T2S) system, which is responsible for the extrusion of folded proteins and protein complexes from the periplasm of Gram-negative bacteria (3)(4)(5). Both machineries are thought to function through the reversible polymerization of pilin subunits into long helical T4P or short T2S pseudopili.…”