The secretion apparatus of Pseudomonas aeruginosa: identification of a fifth pseudopilin, XcpX (GspK family)

Mol Microbiol. 1998 Jan;27(1):31-40. doi: 10.1046/j.1365-2958.1998.00653.x.


The xcp gene products in Pseudomonas aeruginosa are required for the secretion of proteins across the outer membrane. Four of the Xcp proteins, XcpT, U, V and W, present sequence homology to the subunits of type IV pili at their N-termini, and they were therefore designated pseudopilins. In this study, we characterized the xcpX gene product, a bitopic cytoplasmic membrane protein. Remarkably, amino acid sequence comparisons also suggested that the XcpX protein resembles the pilins and pseudopilins at the N-terminus. We show that XcpX could be processed by the prepilin peptidase, PilD/XcpA, and that the highly conserved glycine residue preceding the hydrophobic segment could not be mutated without loss of the XcpX function. We, therefore, classified XcpX (GspK) as the fifth pseudopilin of the system.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Autoradiography
  • Bacterial Outer Membrane Proteins / chemistry*
  • Bacterial Proteins / chemistry*
  • Blotting, Western
  • Electrophoresis, Gel, Two-Dimensional
  • Electrophoresis, Polyacrylamide Gel
  • Fimbriae Proteins
  • Gene Expression
  • Membrane Proteins / chemistry*
  • Molecular Sequence Data
  • Polymerase Chain Reaction
  • Pseudomonas aeruginosa / chemistry
  • Pseudomonas aeruginosa / metabolism*
  • Sequence Analysis, DNA


  • Bacterial Outer Membrane Proteins
  • Bacterial Proteins
  • Membrane Proteins
  • XcpX protein, Pseudomonas aeruginosa
  • Fimbriae Proteins