Periplasmic nonspecific acid phosphatase II from Salmonella typhimurium LT2. Crystallization, detergent reactivation, and phosphotransferase activity

Structural insights into the catalytic mechanism of the bacterial class B phosphatase AphA belonging to the DDDD superfamily of phosphohydrolases

AphA is a magnesium-dependent, bacterial class B acid phosphatase that catalyzes the hydrolysis of a variety of phosphoester substrates and belongs to the DDDD superfamily of phosphohydrolases. The recently reported crystal structure of AphA from Escherichia coli has revealed the quaternary structure of the enzyme together with hints about its catalytic mechanism. The present work reports the crystal structures of AphA from E. coli in complex with substrate, transition-state, and intermediate analogues. The structures provide new insights into the mechanism of the enzyme and allow a revision of some aspects of the previously proposed mechanism that have broader implications for all the phosphatases of the DDDD superfamily.

Quantitative determination of saccharide surfactants in protein samples by liquid chromatography coupled to electrospray ionization mass spectrometry

A direct and highly selective method, combining liquid chromatography (LC) with electrospray ionization mass spectrometry (ESI-MS), has been developed for quantifying saccharide surfactants. Saccharide surfactants, such as n-octyl-beta-d-glucopyranoside (NOG), are widely used to solubilize or refold membrane-bound or lipophilic proteins. In the present study, we have developed an LC-MS method to quantify NOG in protein samples. Protein-bound NOG was completely dissociated from proteins by reversed-phase LC, allowing the total amount of saccharide surfactant in protein samples to be quantified by MS. A chemical analog of NOG was used as an internal standard for improving the reproducibility of the method. Linearity was found in the range of 10 microg/mL-1.0 mg/mL NOG concentrations. Seven major surfactant oligomeric ions were detected under the ionization conditions applied and their relative abundance was essentially unchanged over the range of 0.05-1.0 mg/mL NOG concentrations. Consequently, ions with characteristic mass-to-charge ratios could be used for quantification of NOG. Analytical accuracy of the method was examined by determining the amounts of NOG recovered from apolipoprotein A-I and myoglobin samples spiked with NOG.

Genetic rearrangements in the tyrB-uvrA region of the enterobacterial chromosome: a potential cause for different class B acid phosphatase regulation in Salmonella enterica and Escherichia coli

Unlike in Escherichia coli, in Salmonella enterica production of class B acid phosphatase (AphA) was detectable also in cells growing in the presence of glucose. Characterization of the aphA locus from a S. enterica ser. typhi strain showed that the aphA determinant is very similar to the E. coli homolog, and that its chromosomal location between the highly conserved tyrB and uvrA genes is retained. However, the aphA flanking regions were found to be markedly different in the two species, either between tyrB and aphA or between aphA and uvrA. The differences in the aphA 5'-flanking region, which in S. enterica is considerably shorter than in E. coli (183 vs. 1121 bp) and includes potential promoter sequences not present in E. coli, could be responsible for the different regulation of class B acid phosphatase observed in the two species.

Conserved sequence motifs among bacterial, eukaryotic, and archaeal phosphatases that define a new phosphohydrolase superfamily

Members of a new molecular family of bacterial nonspecific acid phosphatases (NSAPs), indicated as class C, were found to share significant sequence similarities to bacterial class B NSAPs and to some plant acid phosphatases, representing the first example of a family of bacterial NSAPs that has a relatively close eukaryotic counterpart. Despite the lack of an overall similarity, conserved sequence motifs were also identified among the above enzyme families (class B and class C bacterial NSAPs, and related plant phosphatases) and several other families of phosphohydrolases, including bacterial phosphoglycolate phosphatases, histidinol-phosphatase domains of the bacterial bifunctional enzymes imidazole-glycerolphosphate dehydratases, and bacterial, eukaryotic, and archaeal phosphoserine phosphatases and threalose-6-phosphatases. These conserved motifs are clustered within two domains, separated by a variable spacer region, according to the pattern [FILMAVT]-D-[ILFRMVY]-D-[GSNDE]-[TV]-[ILVAM]-[AT S VILMC]-X-¿YFWHKR)-X-¿YFWHNQ¿-X( 102,191)-¿KRHNQ¿-G-D-¿FYWHILVMC¿-¿QNH¿-¿FWYGP¿-D -¿PSNQYW¿. The dephosphorylating activity common to all these proteins supports the definition of this phosphatase motif and the inclusion of these enzymes into a superfamily of phosphohydrolases that we propose to indicate as "DDDD" after the presence of the four invariant aspartate residues. Database searches retrieved various hypothetical proteins of unknown function containing this or similar motifs, for which a phosphohydrolase activity could be hypothesized.

Identification of the gene (aphA) encoding the class B acid phosphatase/phosphotransferase of Escherichia coli MG1655 and characterization of its product

An open reading frame located in the tyrB-uvrA intergenic region of the Escherichia coli MG1655 chromosome was identified as encoding the class B acid phosphatase of this species on the basis of cloning and expression experiments. A protocol for purification of the enzyme (named AphA) was developed, and its properties were analyzed. The enzyme is a 100-kDa homotetrameric protein which apparently requires a metal co-factor for activity. Similarly to other bacterial class B acid phosphatases, it is able to dephosphorylate several organic phosphomonoesters as well as to catalyze the transfer of low-energy phosphate groups from phosphomonoesters to hydroxyl groups of various organic compounds.

Virulence and vaccine potential of phoP mutants of Salmonella typhimurium

We have constructed Salmonella typhimurium phoP mutants and found them to be avirulent and able to induce a protective immune response. BALB/c mice survived challenge with phoP derivatives of the highly virulent S. typhimurium strains SR-11 and SL1344 when inoculated intraperitoneally and per oral with doses equivalent to 10(4) 50% lethal doses (LD50) of the parent virulent strains. The avirulent mutants were able to establish an infection of the Peyer's patches of orally infected animals for up to 10 days after inoculation but were very inefficient at reaching the spleens. Despite the low level of infectivity of these mutants, immunized animals developed a delayed-type hypersensitivity (DTH) response to Salmonella antigens and resisted challenge with up to 10(4) LD50 of the virulent parent strain 30 days after immunization.