A secreted aminopeptidase of Pseudomonas aeruginosa. Identification, primary structure, and relationship to other aminopeptidases

The ywad gene from Bacillus subtilis encodes a double-zinc aminopeptidase

The yet uncharacterized ywad gene from Bacillus subtilis has been cloned and overexpressed in Escherichia coli. The gene product (BSAP) was purified and shown to be an aminopeptidase. The activity of BSAP was optimal at pH 8.4, the enzyme was stable for 20 min at 80 degrees C and its activity was not affected by serine protease and aspartic protease inhibitors, but was completely diminished by the Zn-chelator 1,10-phenanthroline. ZnCl2 was able to restore activity, and the binding stoichiometry of zinc to apo-BSAP indicated two Zn ions per protein molecule. BSAP exhibited high preference toward p-nitroanilide derived Arg, Lys, and Leu synthetic substrates resulting in kcat/Km values of 1-5 x 10(1) s(-1) mM(-1).

A continuous spectrophotometric assay for Pseudomonas aeruginosa LasA protease (staphylolysin) using a two-stage enzymatic reaction

Pseudomonas aeruginosa LasA protease is a secreted metalloendopeptidase that can lyse Staphylococcus aureus cells by cleaving the pentaglycine bridges of their peptidoglycan. It can also degrade elastin and stimulate shedding of cell-surface proteoglycans, activities implicated in pathogenesis of P. aeruginosa infections. The activity of LasA protease can be assayed spectrophotometrically by following the reduction in turbidity of S. aureus cell suspensions. This assay, however, does not permit kinetic studies and its reproducibility is poor. Here we describe a two-stage enzymatic reaction for the continuous measurement of LasA protease activity using a defined substrate, succinyl-Gly-Gly-Phe-4-nitroanilide, supplemented with Streptomyces griseus aminopeptidase. Cleavage of the Gly-Phe bond by LasA protease is followed by hydrolysis of the product Phe-4-nitroanilide by the aminopeptidase and the rate of release of the chromophore (4-nitroaniline) is measured spectrophotometrically using a 96-well microplate reader. Activity of nanogram amounts of LasA protease could be determined within a few minutes. Furthermore, this assay permitted the determination of Km and kcat values for LasA protease, which were 0.46 mM and 11.8s(-1), respectively. Pseudomonas elastase was also active in the assay. However, it was less effective than LasA protease and its activity was inhibited by phosphoramidon. The assay is highly sensitive and reproducible, providing a convenient tool for further studies of LasA protease function(s) and mechanism of action.

Identification of quorum-sensing regulated proteins in the opportunistic pathogenPseudomonas aeruginosaby proteomics

The Gram-negative bacterium Pseudomonas aeruginosa is an opportunistic human pathogen which is responsible for severe nosocomial infections in immunocompromised patients and is the major pathogen in cystic fibrosis. The bacterium utilizes two interrelated quorum-sensing (QS) systems, which rely on N-acyl-homoserine lactone (AHL) signal molecules, to control the expression of virulence factors and biofilm development. In this study, we compared the protein patterns of the intracellular, extracellular and surface protein fractions of the PAO1 parent strain with those of an isogenic lasI rhlI double mutant by means of two-dimensional gel electrophoresis (2-DE). This analysis showed that the intensities of 23.7% of all detected protein spots differed more than 2.5-fold between the two strains. We only considered those protein spots truly QS regulated that were changed in the mutant in the absence of signal molecules but were rescued to the wild-type situation when the medium was supplemented with AHLs. These protein spots were characterized by MALDI-TOF peptide mapping. Twenty-seven proteins were identified that were previously reported to be AHL controlled, among them several well-characterized virulence factors. For one of the identified proteins, the serine protease PrpL, a biochemical assay was established to verify that expression of this factor is indeed QS regulated. Furthermore, it is shown that the quorum-sensing blocker C-30 specifically interferes with the expression of 67% of the AHL-controlled protein spots of the surface fraction, confirming the high specificity of the compound. Importantly, 20 novel QS-regulated proteins were identified, many of which are involved in iron utilization, suggesting a link between quorum sensing and the iron regulatory system. Two of these proteins, PhuR and HasAp, are components of the two distinct haem-uptake systems present in P. aeruginosa. In agreement with the finding that both proteins are positively regulated by the QS cascade, we show that the lasI rhlI double mutant grows poorly with haemoglobin as the only iron source when compared with the wild type. These results add haemoglobin utilization to the list of phenotypes controlled through QS in P. aeruginosa. The surprisingly high number of AHL-regulated proteins relative to the number of regulated genes suggests that quorum-sensing control also operates via post-transcriptional mechanisms. To strengthen this hypothesis we investigated the role of quorum sensing in the post-translational modification of HasAp, an extracellular protein required for the uptake of free and haemoglobin-bound haem.

Application of proteomics to Pseudomonas aeruginosa

The recent completion of the Pseudomonas Genome Project, in conjunction with the Pseudomonas Community Annotation Project (PseudoCAP) has fast-tracked our ability to apply the tools encompassed under the term 'proteomics' to this pathogen. Such global approaches will allow the research community to answer long-standing questions regarding the ability of Pseudomonas aeruginosa to survive diverse habitats, its high intrinsic resistance to antibiotics and its pathogenic nature towards humans. Proteomics provides an array of tools capable of confirming the expression of Open Reading Frames (ORF), the relative levels of their expression, the environmental conditions required for this expression and the sub-cellular location of the encoded gene-products. Since proteins are important cellular effectors, the biological questions we pose can be defined in terms of changes in protein expression detectable by separation to purity using two-dimensional gel electrophoresis (2-DGE) and relation to gene sequences via mass spectrometry. As such, we can compare strains with well-characterized phenotypic differences, growth under a variety of stresses, protein interactions and complexes and aid in defining proteins of unknown function. While the complete genome has only recently been finished, a number of studies have already utilized this information and examined various protein gene-products using proteomics. This review summarizes the application of proteomics to P. aeruginosa and highlights potential areas of future research, including overcoming the traditional technical limitations associated with 2-DGE. More focused approaches that target sub-cellular fractions ('sub-proteomes') prior to 2-DGE can provide further functional information. A review of current and previous proteomic projects on P. aeruginosa is presented, as well as theoretical considerations of the importance of sub-proteomic approaches to enhance these investigations.

Proteome analysis of extracellular proteins regulated by the las and rhl quorum sensing systems in Pseudomonas aeruginosa PAO1

The las and rhl quorum sensing (QS) systems regulate the expression of several genes in response to cell density changes in Pseudomonas aeruginosa. Many of these genes encode surface-associated or secreted virulence factors. Proteins from stationary phase culture supernatants were collected from wild-type and P. aeruginosa PAO1 mutants deficient in one or more of the lasRI, rhlRI and vfr genes and analysed using two-dimensional gel electrophoresis. All mutants released significantly lower amounts of protein than the wild-type. Protein spot patterns from each strain were compared using image analysis and visible spot differences were identified using mass spectrometry. Several previously unknown QS-regulated proteins were characterized, including an aminopeptidase (PA2939), an endoproteinase (PrpL) and a unique 'hypothetical' protein (PA0572), which could not be detected in the culture supernatants of Deltalas mutants, although they were unaffected in Deltarhl mutants. Chitin-binding protein (CbpD) and a hypothetical protein (PA4944) with similarity to host factor I (HF-I) could not be detected when any of the lasRI or rhlRI genes were disrupted. Fourteen proteins were present at significantly greater levels in the culture supernatants of QS mutants, suggesting that QS may also negatively control the expression of some genes. Increased levels of two-partner secretion exoproteins (PA0041 and PA4625) were observed and may be linked to increased stability of their cognate transporters in a QS-defective background. Known QS-regulated extracellular proteins, including elastase (lasB), LasA protease (lasA) and alkaline metalloproteinase (aprA) were also detected.

Purification, characterization, and genetic analysis of a leucine aminopeptidase from Aspergillus sojae

Extracellular leucine aminopeptidase (LAP) from Aspergillus sojae was purified to protein homogeneity by sequential fast protein liquid chromatography steps. LAP had an apparent molecular mass of 37 kDa, of which approximately 3% was contributed by N-glycosylated carbohydrate. The purified enzyme was most active at pH 9 and 70 degrees C for 30 min. The enzyme preferentially hydrolyzed leucine p-nitroanilide followed by Phe, Lys, and Arg derivatives. The LAP activity was strongly inhibited by metal-chelating agents, and was largely restored by divalent cations like Zn(2+) and Co(2+). The lap gene and its corresponding cDNA fragment of the A. sojae were cloned using degenerated primers derived from internal amino acid sequences of the purified enzyme. lap is interrupted by three introns and is transcribed in a 1.3-kb mRNA that encodes a 377-amino-acid protein with a calculated molecular mass of 41.061 kDa. The mature LAP is preceded by a leader peptide of 77 amino acids, predicted to include an 18-amino-acid signal peptide and an extra sequence of 59 amino acids. Two putative N-glycosylation sites are identified in Asn-87 and Asn-288. Southern blot analysis suggested that lap is a single-copy gene in the A. sojae genome. The deduced amino acid sequence of A. sojae LAP shares only 11-33.1% identity with those of LAPs from 18 organisms.