Protein secretion in Pseudomonas aeruginosa: characterization of seven xcp genes and processing of secretory apparatus components by prepilin peptidase

Abstract

The xcp genes are required for the secretion of most extracellular proteins by Pseudomonas aeruginosa. The products of these genes are essential for the transport of exoproteins across the outer membrane after they have reached the periplasm via a signal sequence-dependent pathway. To date, analysis of three xcp genes has suggested the conservation of this secretion pathway in many Gram-negative bacteria. Furthermore, the xcpA gene was shown to be identical to pilD, which encodes a peptidase involved in the processing of fimbrial (pili) subunits, suggesting a connection between pili biogenesis and protein secretion. Here the nucleotide sequences of seven other xcp genes, designated xcpR to -X, are presented. The N-termini of four of the encoded Xcp proteins display similarity to the N-termini of type IV pili, suggesting that XcpA is involved in the processing of these Xcp proteins. This could indeed be demonstrated in vivo. Furthermore, two other proteins, XcpR and XcpS, show similarity to the PilB and PilC proteins required for fimbriae assembly. Since XcpR and PilB display a canonical nucleotide-binding site, ATP hydrolysis may provide energy for both systems.

Photobacterium damselae subsp. damselae Major Virulence Factors Dly, Plasmid-Encoded HlyA, and Chromosome-Encoded HlyA Are Secreted via the Type II Secretion System

“…In different bacterial species it has been shown that upon pilD mutation, in addition to blocking T2SS-dependent secretion, the expression of pili on the cell surface is also prevented (43,46). We investigated whether PilD is involved in P. damselae subsp.…”

A single bifunctional enzyme, PilD, catalyzes cleavage and N-methylation of proteins belonging to the type IV pilin family.

“…The four proteins, PddABCD (also designated XcpTUVW; ref. 19), share a number of similarities with prepilin. Each is between 14 and 25 kDa and has a short leader sequence, a conserved region [-Gly!Phe-Thr-(Leu/lle)-Glu-] flanking the PilD cleavage site ('), and a distinct hydrophobic character of the 16-18 amino acids immediately following the glutamate residue.…”

Stable periplasmic secretion intermediate in the general secretory pathway of Escherichia coli.

“…The second step of the GSP in other Gram-negative bacteria that secrete exclusively non fatty-acylated proteins [e.g. Erwinia chrysanthemi (He et al, 1991a), Xanthomonas campestris (Dums et al, 1991;Hu et al, 1992), Pseudomonas aeruginosa (Filloux et al, 1990;Bally et al, 1992) and Aeromonas hydrophila (Jiang and Howard, 1992)] also depends on proteins similar to those identified in the pullulanase system (see Pugsley, 1992 for review). E. coli K12 and closely related bacteria seem to lack this terminal GSP branch (Pugsley, 1992).…”