Export of the Pseudopilin XcpT of the Pseudomonas aeruginosa Type II Secretion System via the Signal Recognition Particle-Sec Pathway

Abstract

Type IV pilins and pseudopilins are found in various prokaryotic envelope protein complexes, including type IV pili and type II secretion machineries of gram-negative bacteria, competence systems of gram-positive bacteria, and flagella and sugar-binding structures in members of the archaeal kingdom. The precursors of these proteins have highly conserved N termini, consisting of a short, positively charged leader peptide, which is cleaved off by a dedicated peptidase during maturation, and a hydrophobic stretch of approximately 20 amino acid residues. Which pathway is involved in the inner membrane translocation of these proteins is unknown. We used XcpT, the major pseudopilin from the type II secretion machinery of Pseudomonas aeruginosa, as a model to study this process. Transport of an XcpT-PhoA hybrid was shown to occur in the absence of other Xcp components in P. aeruginosa and in Escherichia coli. Experiments with conditional sec mutants and reporter-protein fusions showed that this transport process involves the cotranslational signal recognition particle targeting route and is dependent on a functional Sec translocon.

Signal Recognition Particle-Dependent Inner Membrane Targeting of the PulG Pseudopilin Component of a Type II Secretion System

“…A defect in prepilin peptidase PulO-mediated processing of PulG was also demonstrated in SRP-depleted strains by using a variant of prePulG in which the propeptide was artificially extended with an N-terminal FLAG tag (data not shown). In the accompanying paper, Arts et al show that processing of native XcpT, a close homologue of PulG, by prepilin peptidase also depends on SRP and the Sec machinery (3).…”

Type IV Pilin Proteins: Versatile Molecular Modules

“…In contrast, proteins with the unique type III signal sequence are called prepilins and are not competent for assembly until the signal is cleaved at the cytoplasmic face of the membrane (369). Prepilins are inserted into the cytoplasmic membrane by the Sec system (22,144), and the signal sequence is removed by dedicated aspartyl proteases called prepilin peptidases (301). The positively charged signal sequence is likely important for the correct orientation of pilin proteins, with their C-terminal domains outside the cytoplasmic membrane.…”

Membrane-association determinants of the ω-amino acid monooxygenase PvdA, a pyoverdine biosynthetic enzyme from Pseudomonas aeruginosa

“…Proteinase K accessibility experiments were performed as described (Arts et al, 2007). Briefly, P. aeruginosa PAO1 cells were grown to late-exponential phase at 37 uC in DCAA medium.…”