Alkaline phosphatase possessing alkaline phosphodiesterase activity and other phosphodiesterases in Bacillus subtilis

Clinical pharmacology of exogenously administered alkaline phosphatase

PURPOSE

To evaluate the clinical pharmacology of exogenous alkaline phosphatase (AP).

METHODS

Randomized, double-blind, placebo-controlled sequential protocols of (1) ascending doses and infusion duration (volunteers) and (2) fixed dose and duration (patients) were conducted at clinical pharmacology and intensive care units. A total of 103 subjects (67 male volunteers and 36 patients with severe sepsis) were administered exogenous, 10-min IV infusions (three ascending doses) or 24-72 h continuous (132.5-200 U kg(-1) 24 h(-1)) IV infusion with/without preceding loading dose and experimental endotoxemia for evaluations of pharmacokinetics, pharmacodynamics, safety parameters, antigenicity, inflammatory markers, and outcomes.

RESULTS

Linearity and dose-proportionality were shown during 10-min infusions. The relatively short elimination half-life necessitated a loading dose to achieve stable enzyme levels. Pharmacokinetic parameters in volunteers and patients were similar. Innate immunity response was not significantly influenced by AP, while renal function significantly improved in sepsis patients.

CONCLUSIONS

The pharmacokinetics of exogenous AP is linear, dose-proportional, exhibit a short half-life, and are not influenced by renal impairment or dialysis.

Mutagenesis of Putative Catalytic and Regulatory Residues of Streptomyces chromofuscus Phospholipase D Differentially Modifies Phosphatase and Phosphodiesterase Activities

Phospholipase D from Streptomyces chromofuscus (sc-PLD) is a member of the diverse family of metallo-phosphodiesterase/phosphatase enzymes that also includes purple acid phosphatases, protein phosphatases, and nucleotide phosphodiesterases. Whereas iron is an essential cofactor for scPLD activity, Mn2+ is also found in the enzyme. A third metal ion, Ca2+, has been shown to enhance scPLD catalytic activity although it is not an essential cofactor. Sequence alignment of scPLD with known phosphodiesterases and phosphatases requiring metal ions suggested that His-212, Glu-213, and Asp-389 could be involved in Mn2+ binding. H212A, E213A, and D389A were prepared to test this hypothesis. These three mutant enzymes and wild type scPLD show similar metal content but considerably different catalytic properties, suggesting different roles for each residue. His-212 appears involved in binding the phosphate group of substrates, whereas Glu-213 acts as a ligand for Ca2+. D389A showed a greatly reduced phosphodiesterase activity but almost unaltered ability to hydrolyze the phosphate group in p-nitrophenyl phosphate suggesting it had a critical role in aligning groups at the active site to control phosphodiesterase versus phosphatase activities. We propose a model for substrate and cofactor binding to the catalytic site of scPLD based on these results and on sequence alignment to purple acid phosphatases of known structure.

Sequence-specific binding of prePhoD to soluble TatAd indicates protein-mediated targeting of the Tat export in Bacillus subtilis

The Tat (twin-arginine protein translocation) system initially discovered in the thylakoid membrane of chloroplasts has been described recently for a variety of eubacterial organisms. Although in Escherichia coli four Tat proteins with calculated membrane spanning domains have been demonstrated to mediate Tat-dependent transport, a specific transport system for twin-arginine signal peptide containing phosphodiesterase PhoD of Bacillus subtilis consists of one TatA/TatC (TatAd/TatCd) pair of proteins. Here, we show that TatAd was found beside its membrane-integrated localization in the cytosol were it interacted with prePhoD. prePhoD was efficiently co-immunoprecipitated by TatAd. Inefficient co-immunoprecipitation of mature PhoD and missing interaction to Sec-dependent and cytosolic peptides by TatAd demonstrated a particular role of the twin-arginine signal peptide for this interaction. Affinity of prePhoD to TatAd was interfered by peptides containing the twin-arginine motif but remained active when the arginine residues were substituted. The selective binding of TatAd to peptides derived from the signal peptide of PhoD elucidated the function of the twin-arginine motif as a target site for pre-protein TatAd interaction. Substitution of the binding motif demonstrated the pivotal role of basic amino acid residues for TatA binding. These features suggest that TatA interacts prior to membrane integration with its pre-protein substrate and could therefore assist targeting of twin-arginine pre-proteins.

Transcriptional analysis of the Bacillus subtilis teichuronic acid operon

The cell walls of Gram-positive bacteria consist primarily of a macromolecular matrix comprising similar amounts of peptidoglycan and covalently attached anionic polymers. Under most growth conditions the anionic polymers of Bacillus subtilis are principally teichoic acids; in strain 168 these include a polyglycerol teichoic acid and a glucose/galactosamine-containing teichoic acid. However, when cultures are subjected to phosphate stress the bacterium induces a complex series of responses, one of which is the replacement of at least part of the wall teichoic acid with teichuronic acid, a non-phosphate-containing anionic polymer. In this paper the construction of a transcriptional reporter strain that facilitates the monitoring of the promoter region upstream of the tua operon involved in teichuronic acid synthesis and its controlled expression are reported. The expression of the tua operon was monitored in both phosphate-starved, non-growing batch cultures and phosphate-limited continuous cultures. We show that the transcription of the operon correlates well with the anionic polymer composition of the cell walls.

Localisation of the cell wall-associated phosphodiesterase PhoD of Bacillus subtilis

The localisation of phosphate-starvation-induced phosphodiesterase PhoD from Bacillus subtilis was studied by analysing processing, release and immunogold labelling of the sections. Although the processing of the pre-protein was extremely slow, the major fraction of PhoD could be detected at the surface of the cell wall. The results indicate that inefficient processing of the translocated pre-protein keeps PhoD in a cell wall-associated location. The uncleaved signal peptide might function as a membrane anchor.

Mutational analysis of the phoD promoter in Bacillus subtilis: implications for PhoP binding and promoter activation of Pho regulon promoters

The PhoP-PhoR two-component regulatory system controls the phosphate deficiency response in B. subtilis. A number of Pho regulon genes which require PhoP approximately P for activation or repression have been identified. The studies reported here were initiated to understand the PhoP-DNA interaction necessary for Pho promoter regulation. The regulatory region of phoD was characterized in detail using oligo-directed mutagenesis, DNase I footprinting, and in vivo transcription assays. These data reveal basic principles of PhoP binding relevant to PhoP's interaction with other Pho regulon promoters. Our results show that: (i) a dimer of PhoP approximately P is able to bind two consensus repeats in a stable fashion; (ii) PhoP binding is highly cooperative within the core promoter region, which is located from -66 to -17 on the coding strand and contains four TT(A/T/C)ACA-like repeats; (iii) specific bases comprising the TT(A/T/C)ACA consensus are essential for transcriptional activation, but the specific base pairs of the intervening sequences separating the consensus repeats are not important for either PhoP binding or promoter activation; (iv) the spacing between two consensus repeats within a putative dimer binding site in the core region is important for both PhoP binding and promoter activation; (v) the exact spacing between two dimer binding sites within the core region is important for promoter activation but less so for PhoP binding affinity, as long as the repeats are on the same face of the helix; and (vi) the 5' secondary binding region is important for coordinated PhoP binding to the core binding region, making it nearly essential for promoter activation.

Catalytic promiscuity and the evolution of new enzymatic activities

Several contemporary enzymes catalyze alternative reactions distinct from their normal biological reactions. In some cases the alternative reaction is similar to a reaction that is efficiently catalyzed by an evolutionary related enzyme. Alternative activities could have played an important role in the diversification of enzymes by providing a duplicated gene a head start towards being captured by adaptive evolution.

Sites internal to the coding regions of phoA and pstS bind PhoP and are required for full promoter activity

Bacillus subtilis PhoP and PhoR, a pair of two-component regulatory proteins, regulate the phosphate starvation response. Here, we used two other pho regulon promoters, the phoA and pstS promoters, to examine the mechanism of PhoP-specific activation of its target promoters. Both gel shift and DNase I footprinting assays indicate that PhoP bound to the two promoters. Unphosphorylated PhoP bound only to the multiple TTAACA-like sequences upstream of these two promoters, while phosphorylated PhoP extended the binding region in both the 5' and the 3' direction and, additionally, protected sequences internal to the coding region of these two genes. The PhoP binding sites in the coding region were necessary for full induction from either promoter during phosphate starvation. Deletion of these sites eliminated approximately 75% and 45% of the induced promoter activity of the phoA and pstS promoters respectively. In vitro transcription assays using the phoA promoters with various 3' ends confirmed the requirement of the PhoP-P binding to the coding region for full promoter activity. The multiple TTAACA-like sequences in the phoA and pstS promoters were essential for promoter activity, and deletion of one or more of these sequences in either promoter eliminated the promoter activity. Two pairs of TTAACA-like sequences were required for efficient PhoP binding and were suggested to be one B. subtilis Pho box. Based on our data, we have proposed a model for activation of the phoA and the pstS promoter by PhoP.

Influence of Bacillus subtilis phoR on cell wall anionic polymers

In Bacillus subtilis the Pho regulon is controlled by a sensor and regulator protein pair, PhoR and PhoP, that respond to phosphate concentrations. To facilitate studies of the Pho regulon, a strain with an altered PhoR protein was isolated by in vitro mutagenesis. The mutation in this strain (phoR12) leads to the production of a PhoR sensor kinase that, unlike the wild-type, is functionally active in phosphate-replete conditions. The lesion in PhoR12 was shown to be a single base change that results in an Arg to Ser substitution in a region of PhoR that is highly conserved in histidine sensor kinases. While a phoR-negative mutant was unable to induce the synthesis of cell wall teichuronic acid under phosphate-limited conditions, the phoR12 mutant showed a relative increase in teichuronic acid and a decrease in teichoic acid, even under phosphate-replete conditions. The latter suggests that some or all of the genes required for teichuronic acid synthesis are members of the Pho regulon.

Production of two extracellular alkaline phosphatases by a psychrophilic arthrobacter strain

We surveyed our collection of psychrophilic bacteria to determine the types of phosphatases they produce and whether any had heat-labile activities with potential applications. Assays at different temperatures showed that the activity from one isolate was optimal at 45(deg)C and decreased dramatically above 55(deg)C. This isolate, D10, had the rod-coccus morphological cycle and cell wall amino acids associated with members of the Arthrobacter genus. Interestingly, we found that this strain made two extracellular phosphatases that could be separated by ammonium sulfate fractionation and migration during polyacrylamide gel electrophoresis. One enzyme, designated D10A, hydrolyzed both X-phos (5-bromo-4-chloro-3-indolyl phosphate) and para-nitrophenyl phosphate as substrates and had activity over a broad pH range of 7 to 11. The second enzyme, D10B, lacked activity against X-phos and had a narrow pH range of about 8 to 9. In addition, the D10B enzyme required calcium for activity. The levels of activity of both enzymes decreased for cells grown in media containing more than 100 (mu)M P(infi). These results not only demonstrate the existence of different enzymes from one Arthrobacter strain but also suggest ways in which other studies may have missed phosphatases with unknown requirements.

The organization of the Bacillus subtilis 168 chromosome region between the spoVA and serA genetic loci, based on sequence data

Three different lambda phage clones with overlapping inserts of Bacillus subtilis DNA, which cover the region from spoIIAA to serA, have been isolated. The nucleotide sequence of their inserts, starting after spoVAF and ending at serA, has been determined. A contiguous sequence of 35,354 bp was established, including previously analysed overlapping adjacent regions. Within the newly determined sequence 31 open reading frames (ORFs) with putative ribosome-binding sites have been found. Nine of them correspond to previously sequenced and characterized genes: spo-VAF, lysA, sipS, ribG, ribB, ribA, ribH, ribTD and dacB. Comparison of the amino acid sequences of the products encoded by the other ORFs to known proteins allowed putative functions to be assigned to seven of these ORFs. Among these are the following: (i) the ppiB gene, encoding a cytoplasmic peptidylprolyl isomerase; (ii) two pairs of signal-transducers, one homologous to phoR-phoP of B. subtilis, encoding regulators of phosphatase biosynthesis, and the second to the fecI-fecR of Escherichia coli, which is responsible for the regulation of the citrate-dependent iron (III) transport system; (iii) aroC and serA genes, involved in the biosynthesis of aromatic amino acids and serine, respectively, the function of which has been confirmed by constructing corresponding mutants with disrupted ORFs. The organization of putative operons has been postulated on the basis of the sequences of their transcription terminators, promoters and regulatory elements.

Nucleotide sequence of the Bacillus subtilis phoR gene

The nucleotide sequence of phoR, the positive and negative regulatory gene for alkaline phosphatase and phosphodiesterase formation in Bacillus subtilis, was determined. The sequence data predicted an open reading frame of 1,740 base pairs (579 amino acids) which overlaps the 5 base pairs of the preceding phoP coding sequence. The deduced amino acid sequence was significantly homologous with that of the Escherichia coli phoR gene product, which is the sensory element for the pho regulon.

Cloning and nucleotide sequence of phoP, the regulatory gene for alkaline phosphatase and phosphodiesterase in Bacillus subtilis

Two DNA fragments which complement the alkaline phosphatase-negative mutation phoP of Bacillus subtilis were cloned from a B. subtilis chromosome with the prophage vector phi CM (a derivative of phi 105). One of the fragments contained the regulatory gene phoR in addition to phoP. Nucleotide sequence analysis of the phoP region revealed that the phoP gene product consists of 241-amino-acid residues and that the sequence of these amino acids is extensively homologous with the sequence of the phoB gene product. This protein is the positive regulator for the phosphate regulon in Escherichia coli. It therefore appears that phoP is a regulatory gene for alkaline phosphatase synthesis in B. subtilis.

Alkaline phosphatase and 5'-nucleotide phosphodiesterase from bovine intestine are cross-reactive

Polyclonal antibodies to native alkaline phosphatase and to native 5'-nucleotide phosphodiesterase were found to strongly cross-react with both enzymes. The antibodies also cross-react with both denatured enzymes, with glycopeptides from 5'-nucleotide phosphodiesterase, and with the oligosaccharides remaining after Pronase E digestion of the phosphodiesterase. They do not cross-react with either enzyme after their oligosaccharides have been modified or removed by periodate or trifluoromethanesulfonic acid treatment. Antibodies to denatured 5'-nucleotide phosphodiesterase do not bind to the native phosphodiesterase or alkaline phosphatase but do cross-react with denatured alkaline phosphatase even after removal or modification of the carbohydrate moieties. These results suggest that antibodies to denatured 5'-nucleotide phosphodiesterase may recognize amino acid sequence homology between alkaline phosphatase and 5'-nucleotide phosphodiesterase. However, antibodies to native enzymes apparently recognize cross-reactive determinants of the native enzymes which are carbohydrate in nature. This is the first report of antimammalian alkaline phosphatase antibodies which recognize the carbohydrate moieties of the enzyme.

Alkaline phosphatase secretion-negative mutant of Bacillus licheniformis 749/C

An alkaline phosphatase secretion-blocked mutant of Bacillus licheniformis 749/C was isolated. This mutant had defects in the phoP and phoR regions of the chromosome. The selection procedure was based on the rationale that N-methyl-N'-nitro-N-nitrosoguanidine can induce mutations of closely linked multiple genes. The malate gene and the phoP and phoR genes are located at the 260-min position in the Bacillus subtilis chromosome; hence, the malate gene could be used as a marker for the mutation of the phoP and phoR regions of the chromosome. In a two-step selection procedure, strains defective in malate utilization were first selected with the cephalosporin C procedure. Second, these malate-defective strains were further screened in a dye medium to select strains with defects in alkaline phosphatase secretion. One stable mutant (B. licheniformis 749/cNM 105) had a total secretion block for alkaline phosphatase and had the following additional characteristics: (i) the amount of alkaline phosphatase synthesized was comparable to that in the wild type; (ii) the alkaline phosphatase was membrane bound; (iii) the mutant strain alkaline phosphatase, in contrast to that of the wild type, could not be extracted with MgCl2, although the amounts of protein extracted from each strain were comparable; (iv) the sodium dodecyl sulfate-polyacrylamide gel pattern of MgCl2-extracted proteins from the mutant strain was different from that of the wild-type proteins; (v) the mutant, unlike the wild type, could not use malate as a sole source of carbon; and (vi) the outside surface of the wall of the mutant cells contained an additional electron-dense layer that was not present on the wild-type cell wall surface.

A family of phosphohydrolases from bovine intestinal mucosa: 5'-nucleotidase

Bovine intestinal 5'-nucleotidase has been partially purified and characterized for comparison with two other phosphohydrolases from the same tissue, alkaline phosphatase and 5'-nucleotide phosphodiesterase, which are closely related structurally and mechanistically. Kinetic studies with a variety of nucleotides and phosphonate analogs show that, although 5'-nucleotidase is a monoesterase like alkaline phosphatase, it more closely resembles 5'-nucleotide phosphodiesterase in its high affinity and specificity for nucleotide binding. 5'-Nucleotidase is bound very strongly by an affinity column containing a bound phosphonate analog of ADP but is not bound by an affinity column containing a non nucleotide phosphonate which selectively binds alkaline phosphatase. 5'-Nucleotidase is strongly bound by immobilized antibodies prepared against 5'-nucleotide phosphodiesterase, and is less strongly bound by immobilized antibodies prepared against alkaline phosphatase. We conclude that 5'-nucleotidase is structurally more similar to 5'-nucleotide phosphodiesterase than to another monoesterase, alkaline phosphatase.

Purification and characterization of extracellular soluble and membrane-bound insoluble alkaline phosphatases possessing phosphodiesterase activities in Bacillus subtilis

A membrane-bound insoluble alkaline phosphatase (APase) and an extracellular soluble APase were purified, respectively, from a membrane preparation of Bacillus subtilis 6160-BC6, which carries a mutation to produce APase constitutively, and from a culture fluid of a mutant strain. RAN 1, isolated from strain 6160-BC6, which produces an extracellular soluble APase. The two preparations were homogeneous, as judged by sodium dodecyl sulfate discontinuous gel electrophoresis and by gel electrophoreses in the presence of 8 M urea at pH 9.3 and 4.3. RAN 1 APase was crystallized. Both preparations possessed phosphatase and phosphodiesterase activities, and their pH optima were both at 9.5. They were competitively inhibited by phosphate or arsenate and were activated by the addition of Ca2+ but not by Zn2+. The APase and alkaline phosphodiesterase activities seemed to be contained in the same protein molecule. The molecular weight of 6160-BC6 APase was estimated to be 46,000 +/- 1,000, and that of RAN 1 APase was estimated to be 45,000 +/- 1,000. The largest difference between the 6160-BC6 and RAN 1 APase's was in solubility in low-ionic-strength solutions. Present results suggest that each enzyme is composed of a single polypeptide chain and that 6160-BC6 APase aggregates in solutions of low ionic strength.