Disease relevance of pilD

• The leader sequence is first proteolytically removed by specialized endopeptidases, of which the prototype is encoded by the pilD gene of Pseudomonas aeruginosa [1].
• The last gene (pulO) of the pulC-O pullulanase secretion gene operon of Klebsiella oxytoca codes for a protein that is 52% identical to the product of the pilD/xcpA gene required for extracellular protein secretion and type IV pilus biogenesis in Pseudomonas aeruginosa [2].

High impact information on pilD

• In the Gram-negative pathogen Pseudomonas aeruginosa, mutants in the gene for the prepilin peptidase (pilD) are pleiotropic, as they not only fail to process pilin but also accumulate in the periplasm, in their mature form, several toxins and hydrolytic enzymes that are normally exported to the external medium (excreted) [3].
• In this paper we report the isolation and characterization of transposon-induced excretion mutants with phenotypes similar to that of a pilD gene mutant [3].
• Mutagenesis of pilD resulting in specific amino acid substitutions in all of the Cys residues in PilD show that the 4 conserved cysteines in the cytoplasmic domain are required for full peptidase activity in vivo and for complete peptidase and methyltransferase activities in vitro [4].
• The dimeric XcpT/PilA complex was also formed in a pilD mutant, which lacks the leader peptidase enzyme, demonstrating that the leader peptide at the N-terminus or PilA or XcpT did not have to be removed for the dimerization to occur [5].
• In Pseudomonas aeruginosa this export pathway and type IV pilus biogenesis are dependent on the product of the pilD gene [6].

Biological context of pilD

• An A. hydrophila genomic library was transferred into a P. aeruginosa pilD mutant that is defective for type IV pilus biogenesis [6].
• In addition, a pilD mutant exhibits reduced adherence to HEp-2 cells, a block in secretion of several exoenzymes that follow the type II secretion pathway, and decreased virulence [7].
• In Pseudomonas aeruginosa, the genes pilB, pilC, and pilD encode proteins necessary for posttranslational modification and assembly of pilin monomers into pilus organelles (D. Nunn, S. Bergman, and S. Lory, J. Bacteriol. 172:2911-2919, 1990) [8].
• Mutational analysis of the pilD gene showed that pilD is essential for secretion of cholera toxin and hemagglutinin-protease, mannose-sensitive hemagglutination (MSHA), production of toxin-coregulated pili, and colonization of infant mice [9].

Anatomical context of pilD

• The rates of cleavage were compared for purified enzyme and substrate as well as for enzyme and substrate contained within total membranes extracted from P. aeruginosa strains overexpressing the cloned pilD or pilA genes [10].

Associations of pilD with chemical compounds

• The periplasmic form of exotoxin A was fully mature in size, contained all cysteines in disulfide bonds, and was toxic in a tissue culture cytotoxicity assay, suggesting that in pilD mutants, exotoxin A was folded into its native conformation [8].
• A specialized leader peptidase/methylase, product of the pilD gene, has been shown to cleave the leader peptide from prepilin and to methylate the N-terminal phenylalanine of the mature pilin [11].

Other interactions of pilD

• This report describes a new pilus-assembly gene, pilG, that immediately precedes the gonococcal (Gc) pilD gene encoding the pre-pilin leader peptidase [12].
• Insertion of the omega fragment containing strong transcriptional terminators into pilB, pilC, and pilD failed to have a polar effect on expression of downstream genes, as determined by the ability of each cloned gene to complement, in trans, the corresponding insertionally inactivated chromosomal copy [13].
• The D. nodosus genes fimN, fimO, and fimP are homologs of the Pseudomonas aeruginosa fimbrial assembly genes, pilB, pilC, and pilD, respectively [14].
• Southern blot analysis demonstrates the widespread presence of both pilA and pilD in clinical as well as environmental strains of V. vulnificus [7].
• We show that PilD, encoding a putative pilin-specific leader peptidase, also controls export of alkaline phosphatase, phospholipase C, elastase, and exotoxin A. pilD mutants accumulate these proteins in the periplasmic space, while secretion of periplasmic and outer membrane proteins appears to be normal [8].

References