Bacterial outer membrane ushers contain distinct targeting and assembly domains for pilus biogenesis

J Bacteriol. 2002 Nov;184(22):6260-9. doi: 10.1128/JB.184.22.6260-6269.2002.


Biogenesis of a superfamily of surface structures by gram-negative bacteria requires the chaperone/usher pathway, a terminal branch of the general secretory pathway. In this pathway a periplasmic chaperone works together with an outer membrane usher to direct substrate folding, assembly, and secretion to the cell surface. We analyzed the structure and function of the PapC usher required for P pilus biogenesis by uropathogenic Escherichia coli. Structural analysis indicated PapC folds as a beta-barrel with short extracellular loops and extensive periplasmic domains. Several periplasmic regions were localized, including two domains containing conserved cysteine pairs. Functional analysis of deletion mutants revealed that the PapC C terminus was not required for insertion of the usher into the outer membrane or for proper folding. The usher C terminus was not necessary for interaction with chaperone-subunit complexes in vitro but was required for pilus biogenesis in vivo. Interestingly, coexpression of PapC C-terminal truncation mutants with the chromosomal fim gene cluster coding for type 1 pili allowed P pilus biogenesis in vivo. These studies suggest that chaperone-subunit complexes target an N-terminal domain of the usher and that subunit assembly into pili depends on a subsequent function provided by the usher C terminus.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Bacterial Outer Membrane Proteins / metabolism
  • Circular Dichroism
  • Epitope Mapping
  • Escherichia coli / genetics
  • Escherichia coli / metabolism*
  • Escherichia coli Proteins*
  • Fimbriae, Bacterial / metabolism*
  • Humans
  • Molecular Chaperones / chemistry*
  • Molecular Chaperones / genetics
  • Molecular Chaperones / immunology
  • Molecular Chaperones / metabolism*
  • Molecular Sequence Data
  • Porins / chemistry*
  • Porins / genetics
  • Porins / immunology
  • Porins / metabolism*
  • Sequence Analysis, DNA


  • Bacterial Outer Membrane Proteins
  • Escherichia coli Proteins
  • Molecular Chaperones
  • Porins
  • atpG protein, E coli

Associated data

  • GENBANK/AF481883