Purification and properties of an alkaline phosphatase of Bacillus licheniformis

Translational regulation of periplasmic folding assistants and proteases as a valuable strategy to improve production of translocated recombinant proteins in Escherichia coli

Background

Advantages of translocation of recombinant proteins to the periplasm in Escherichia coli include simplified downstream processing, and improved folding and in vivo activity of the target protein. There are, however, problems encountered in the periplasmic production that can be associated with the incorrect formation of disulfide bonds, incomplete cleavage of the signal peptide, and proteolytic degradation. A common strategy used to overcome these difficulties involves manipulating the cellular levels of proteases and periplasmic folding assistants like chaperones, signal peptide peptidases or thiol-disulfide oxidoreductases. To date, this has been achieved by plasmid-based over-expression or knockouts of the relevant genes.

Results

We changed the translation efficiencies of five native E. coli proteins, DsbA, DsbB, Skp, SppA, and DegP, by modifying the strength of their ribosome binding sites (RBS). The genomic RBS sequences were replaced with synthetic ones that provided a predicted translation initiation rate. Single- and double-gene mutant strains were created and tested for production of two pharmaceutically relevant proteins, PelB-scFv173–2-5-AP and OmpA-GM-CSF. Almost all the single-gene mutant strains showed improved periplasmic production of at least one of the recombinant proteins. No further positive effects were observed when the mutations were combined.

Conclusions

Our findings confirm that our strain engineering approach involving translational regulation of endogenous proteins, in addition to plasmid-based methods, can be used to manipulate the cellular levels of periplasmic folding assistants and proteases to improve the yields of translocated recombinant proteins. The positive effects of SppA overexpression should be further investigated in E. coli.

Mg2+ decreases arrhenius energies of activation for high temperature catalysis of phosphatases in Thermoactinomyces vulgaris

The nonspecific acid and alkaline phosphatases of Thermoactinomyces vulgaris were found to be optimally active at 65 degrees C and 70 degrees C, respectively, indicating the thermophilic nature of these enzymes in this obligate thermophile. Mg(2+), when added in the assay mixture (in the form of MgCl(2)), increased the specific activities of these enzymes without affecting their respective temperature optima. This divalent cation decreased the Arrhenius energies of activation (E ( A )) of both acid and alkaline phosphatases, as substantiated by Mg(2+)-dependent decrease in the slopes of their Arrhenius plots, which were found to be linear. Thus, Mg(2+)-dependent stimulation of high temperature catalysis of T. vulgaris phosphatases appeared to be accomplished by the decrease in their E ( A )values by this divalent cation, and such unique feature of these enzymes might be associated with their evolutionary adaptation in this thermophilic actinomycete to support its growth at elevated temperatures. The catalytic role of Mg(2+ )in enhancing the phosphatase activities was specified by the fact that this metal ion was able to recover the enzyme activities inhibited by dialysis and EDTA.

Differential expression of thermophilic phosphatases in the wild type and auxotrophic mutant strains of Thermoactinomyces vulgaris

In the wild type strain (stock no. 1227) of Thermoactinomyces vulgaris, as reported earlier [Sinha and Singh (1980) Biochem. J. 190, 457-460], all phosphatase isoenzymes (three alkaline - AlpI, AlpII and AlpIII, and one acidic - Acp) are present. However, the auxotrophic mutants, the strains 1286 (thi(-)), 1279 (nic(-), ura(-)) and 1278 (thi(-), ura(-)) exhibited two alkaline phosphatase isoenzymes (AlpII and AlpIII), but AlpI was lacking. In the strain 1261 (nic(-), thi(-)), only AlpIII was expressed, and AlpI and AlpII isoenzymes were missing. The results suggest that the strains, which require either thiamine (1286 and 1278) or nicotinamide (1279) for their growth, were AlpI(-) mutants; and the strain (1261), which requires both thiamine and nicotinamide for its growth, was AlpI(-)/AlpII(-) double mutant. There was no direct correlation between uracil auxotrophy and the expression of phosphatases. The uniform expression of AlpIII and Acp in all the strains, irrespective of their nutrient requirements, suggest that these constitutive phosphatases are species-specific. The specific activities of the thermophilic acid and alkaline phosphatases were maximum in the wild type strain (1227) of T. vulgaris. The next in phosphatase activity was the strain 1279 (an AlpI(-) mutant), followed by their decrease, in order, in the strains 1286 and 1278 (which were also AlpI(-) mutants); while least activity of these enzymes was observed in the obligate thermophile strain 1261 (AlpI(-)/AlpII(-) double mutant).

Cloning and expression of a neutral phosphatase gene from Treponema denticola

We have isolated and characterized a neutral phosphatase gene, phoN, from Treponema denticola ATCC 35405. The gene was isolated from a T. denticola clone bank constructed in the medium-copy-number plasmid vector pMCL19. Subcloning and nucleotide sequencing of the DNA insert from one phosphatase clone, pTph14, revealed that the activity corresponded to an open reading frame consisting of 1,027 bp coding for a 37.9-kDa protein. Hydrophobicity analysis indicated that the protein exhibits some hydrophobic regions. Indeed, partial purification of the phosphatase suggested that the enzyme was membrane associated both in T. denticola and in the Escherichia coli clone. The pH optimum of the enzyme, approximately pH 6.4, indicated that it corresponded to a neutral phosphatase activity from T. denticola. An examination of possible natural substrates for the enzyme suggested that this enzyme hydrolyzes nucleoside di- and triphosphates. Northern (RNA) blot analysis revealed that this phosphatase gene is not likely to be present in an operon structure.

Evidence for two structural genes for alkaline phosphatase in Bacillus subtilis

Two secreted alkaline phosphatase proteins were purified from cultures of Bacillus subtilis JH646MS. The two proteins showed slight differences in subunit molecular weight, substrate specificity, and charge characteristics. A total of 62% of the first 22 amino-terminal amino acids were identical. Both sequences showed conservation of structural features identified in Escherichia coli and human alkaline phosphatases. One alkaline phosphatase was a monomer and the other was a dimer. Southern analysis of genomic DNA with degenerative oligomers based on the amino acid sequences suggest that there are two structural genes for alkaline phosphatase in the genome of B. subtilis.

Factors influencing the activity of cellular alkaline phosphatase during growth and sporulation of Bacillus cereus

Alkaline phosphatase (EC 3.1.3.1) is synthesized in media with a low phosphate concentration (0.37 mM of total and 19 microM of inorganic phosphate, respectively) already during the exponential phase of growth of Bacillus cereus. The enzyme is repressed by higher phosphate concentrations (3.7 mM) during the whole growth period; during sporogenesis the enzyme activity in cells slightly increases even under these conditions. During growth the enzyme is not secreted into the medium, a minor amount being released after cessation of growth. The enzyme activity can be increased by adding Zn2+ ions (10 microM). When during growth without phosphate the pH of the medium decreases below 5.0, the enzyme activity temporarily decreases and growth is slowed down, followed by a subsequent increase of the enzyme activity. In this case the onset of sporulation is also delayed.

Membrane-associated alkaline phosphatase from Bacillus licheniformis that requires detergent for solubilization: lactoperoxidase 125I localization and molecular weight determination

When membranes of Bacillus licheniformis MC14 were extracted exhaustively with 1 M magnesium, approximately 80% of the membrane-associated alkaline phosphatase (orthophosphoric-monoester phosphohydrolase [alkaline optimum], E.C. 3.1.3.1) was solubilized. The remaining activity could be extracted with a cationic detergent, hexadecylpyridinium chloride, without loss of enzymatic activity. The detergent-extractable alkaline phosphatase was immunoprecipitable with antibody to the salt-extractable alkaline phosphatase or the secreted alkaline phosphatase, had an approximate molecular weight of 60,000, and was localized 100% on the outer surface of the cytoplasmic membrane.

Multiple forms of human intestinal alkaline phosphatase: chemical and enzymatic properties, and circulating clearances of the fast- and slow-moving enzymes

Two forms of alkaline phosphatase (orthophosphoric monoester phosphohydrolase (alkaline optimum, EC 3.1.3.1) have been purified from human small intestine by column chromatography on DEAE-cellulose and tyraminyl derivative affinity gel, and by preparative disc gel electrophoresis. Intestinal phosphatases were electrophoretically separated into two components, fast- and slow-moving enzymes, with apparent molecular weights of 140000 and 168000 and with subunit weights of 68000 and 80000, respectively. Analyses of carbohydrate and amino acid revealed marked differences in the two enzymes. Enzymatic properties and affinities for an anti-blood group antibody were also found to differ. Papain digestion released a hydrophobic small peptide from the slow-moving enzyme and its enzymatic properties resembled those of the fast-moving enzyme. Circulating clearance (T1/2) of the slow- and fast-moving enzymes from adult intestine was found to be 7.5 h and 1.3 h, respectively; that of fetal intestinal enzyme was 2.8 h. Sialidase, sialidase/beta-galactosidase, or sialidase/beta-galactosidase/N-acetyl-beta-glucosaminidase treatment of the fetal enzyme reduced the value to about 40 min. Further, digestion with alpha-fucosidase, alpha-mannosidase or both restored it to nearly the original level. Organ distribution of injected 125I-labelled enzymes indicates that the desialylated hepatic enzyme was selectively distributed in liver, while the degalactosylated intestinal enzyme was incorporated into liver lymph fluid, and small intestine. These results suggest that the pathway of circulating clearance of alkaline phosphatase has several routes.

A soluble alkaline phosphatase from Bacillus licheniformis MC14. Histochemical localization, purification, characterization and comparison with the membrane-associated alkaline phosphatase

Growth conditions affect the quantity and distribution of alkaline phosphatase (orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1) in Bacillus licheniformis MC14. The soluble alkaline phosphatase, which has been found in biochemical localization studies between the cell wall and cell membrane (Glynn, J.A., Schaffel, S.D., McNicholas, J.M. and Hulett, F.M. (1977) J. Bacteriol. 129, 1010-1019), was localized via electron microscope histochemistry in cells cultured under conditions which result in increased quantities of this activity. This soluble alkaline phosphatase was stabilized with 20% glycerol and purified to homogeneity as determined by sodium dodecyl sulfate(SDS)-polyacrylamide gel electrophoresis. The purified enzyme is soluble in dilute buffer. This soluble alkaline phosphatase has been characterized and compared to the membrane-associated alkaline phosphatase from this organism.

Effect of cobalt on synthesis and activation of Bacillus licheniformis alkaline phosphatase

The effect of CO2+ on the synthesis and activation of Bacillus licheniformis MC14 alkaline phosphatase has been shown by the development of a defined minimal salts medium in which this organism produces 35 times more (assayable) alkaline phosphatase than when grown in a low-phosphate complex medium or in the defined medium without cobalt. Stimulation of enzyme activity with cobalt is dependent on a low phosphate concentration in the medium (below 0.075 mM) and continued protein synthesis. Cobalt stimulation resulted in alkaline phosphate production being a major portion of total protein synthesized during late-logarithmic and early-stationary-phase culture growth. Cells cultured in the defined medium minus cobalt, or purified enzyme partially inactivated with a chelating agent, showed a 2.5-fold increase in activity when assayed in the presence of cobalt. Atomic spectral analysis indicated the presence of 3.65 +/- 0.45 g-atoms of cobalt associated with each mole of purified active alkaline phosphatase. A biochemical localization as a function of culture age in this medium showed that alkaline phosphatase was associated with the cytoplasmic membrane and was also found as a soluble enzyme in the periplasmic region and secreted into the growth medium.

Lactoperoxidase-125I localization of salt-extractable alkaline phosphatase on the cytoplasmic membrane of Bacillus licheniformis

Previous histochemical and biochemical localizations of alkaline phosphatase in Bacillus licheniformis MC14 have shown that the membrane-associated form of the enzyme is located on the inner surface of the cytoplasmic membrane, and soluble forms are located in the periplasmic space and in the growth medium. The distribution of salt-extractable alkaline phosphatase on the surfaces of the cytoplasmic membrane of B. licheniformis MC14 was determined by using lactoperoxidase-125I labeling techniques. Cells harvested during rapid alkaline phosphatase production were converted to protoplasts or lysed protoplasts and labeled. Analysis of the data obtained indicated that 30% of the salt-extractable, membrane-associated alkaline phosphatase was located on the outer surface of the cytoplasmic membrane, whereas 70% of the membrane-associated enzyme was localized on the inner surface. Controls for protoplast integrity (release of tritiated thymidine or examination of cytoplasmic proteins for label content) indicated excellent protoplast stability. Controls indicated that chemical labeling was not a factor in the apparent distribution of alkaline phosphatase on the membrane. These results support the previously reported histochemical localization of alkaline phosphatase on the membrane inner surface. The presence of alkaline phosphatase on the membrane outer surface is reasonable, considering the soluble forms of the enzyme found in the periplasmic region and in the culture medium.

Effects of Grazing by Estuarine Gammaridean Amphipods on the Microbiota of Allochthonous Detritus

Estuarine gammaridean amphipods grazing at natural population density on detrital microbiota affected the microbial community composition, biomass, and metabolic activity without affecting the physical structure of the leaves. Total microbial biomass estimated by adenosine triphosphate and lipid phosphate or observed by scanning electron microscopy was greater on grazed than on ungrazed detritus. The rates of oxygen consumption, poly-β-hydroxybutyrate synthesis, total lipid biosynthesis, and release of 14 CO 2 from radioactively prelabeled microbiota were higher on grazed than on ungrazed leaves, indicating stimulation of the metabolic activity of grazed detrital microbes. This was true with rates based either on the dry leaf weight or microbial biomass. Alkaline phosphatase activity was lower in the grazed system, consistent with enhanced inorganic phosphate cycling. The loss of 14 C from both total lipid and poly-β-hydroxybutyrate of microorganisms prelabeled with 14 C was greater from grazed than ungrazed microbes. There was a faster decrease in the 14 C-glycolipid than in the 14 C-neutral lipid or 14 C-phospholipid fractions. Analysis of specific phospholipids showed losses of the metabolically stable [ 14 C]glycerolphosphorylcholine derived from phosphatidylcholine and much more rapid metabolism of the bacterial lipid phosphatidylglycerol measured as [ 14 C]glycerolphosphorylglycerol with amphipod grazing. The biochemical data supported scanning electron microscopy observations of a shift as the grazing proceeded from a bacterial/fungal community to one dominated by bacteria.

Phosphate utilization and constitutive synthesis of phosphatases in Thermoactinomyces vulgaris Tsilinsky

Thermoactinomyces vulgaris utilized both organic and inorganic phosphates with equal efficiency for its growth. The specific activities of the thermophilic acid and alkaline phosphatases were found to be maximum at 1 mM concentration of each phosphate source. All the phosphatase isoenzymes (three alkaline and one acidic) were observed irrespective of the substrate source and concentration, suggesting constitutive synthesis of the enzymes. During growth and differentiation, both acid and alkaline phosphatases exhibited uniformly stable patterns of isoenzymes with slight variations in their specific activities.

Alkaline phosphatase from Bacillus licheniformis. Solubility dependent on magnesium, purification and characterization

The membrane-associated alkaline phosphatase (orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1) from Bacillus licheniformis MC14, a facultative thermophile, was purified to homogeneity in buffer containing 0.2 M Mg2+. The alkaline phosphatase purified in this manner is insoluble upon removal of the magnesium by dialysis. This insoluble alkaline phosphatase has been characterized and compared to the previously purified heat-solubilized enzyme (Hulett-Cowling, F.M. and Campbell, L.L. (1971) Biochemistry 10, 1364--1371).

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.

Control of teichoic acid synthesis in Bacillus licheniformis ATCC 9945

Analysis of cell walls of Bacillus licheniformis ATCC 9945 grown under phosphate limitation showed that teichoic acid could be replaced by teichuronic acid under these conditions. Teichuronic acid, however, was always present in the walls to some extent irrespective of the growth conditions. The enzymes involved in teichoic acid synthesis were investigated and the synthesis of these was shown to be repressed when the intracellular Pi level fell. CDP-glycerol pyrophosphorylase was studied in some detail and evidence is presented to show that the enzyme is inactivated under phosphate-limited conditions. The mechanism of inactivation is unknown but it has been shown that it does not require protein synthesis de novo.

Biochemical localization of the alkaline phosphatase of Bacillus licheniformis as a function of culture age

Biochemical localization of the enzyme as a function of age of cell culture showed the alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) activity of Bacillus licheniformis MC14 predominantly in the particulate cell fraction in early- and mid-log cells. However, in late-log and stationary cells, increasing amounts of activity were found in the soluble fraction of lysed cells. Upon protoplast formation of these cells, the activity was released into the soluble fraction. No alkaline phosphatase activity was found in either the cytoplasmic fraction or in the cell medium during any phase of cell growth. The soluble fraction released on protoplast formation that contained alkaline phosphatase activity showed immunological cross-reactivity with antibody to the purified heat--salt-solubilized membrane alkaline phosphatase (F. M. Hulett-Cowling and L. L. Campbell, 1971). Theparticulate membrane fraction containing a firmly associated alkaline phosphatase also showed similar cross-reactivity. Further, the effectiveness of nonionic detergents, ionic detergents, bile salts, and various concentrations of magnesium and sodium as solubilizing agents for this membrane-bound alkaline phosphatase was investigated. Hexadecyl pyridinium chloride (0.03 M) and magnesium and sodium salts (above 0.2 M) were effective solubilizing agents. The substrate specificities of the various fractions were determined and compared to the substrate specificities of the purified membrane alkaline phosphatase.

Electron microscope histochemical localization of alkaline phosphatase(s) in Bacillus licheniformis

Sites of alkaline phosphatase (APase) activity in a facultative thermophilic strain of Bacillus licheniformis MC14 have been localized by electron microscope histochemistry, using a lead capture method. The effects of 3% glutaraldehyde and 3.0 mM lead on APase activity were investigated, and these compounds were found to significantly inhibit enzyme activity, 68 and 18%, respectively. A number of parameters were varied in studies to localize APase activity, including: growth temperature (55 and 37 degrees C); substrate concentration in the histochemical mixture (0.06, 0.15, 0.30, 1.00 mM); fixatives; protoplast preparations and whole cells; phosphate-repressed and -derepressed cells; and age of vegetative cells (mid-log and late log). These variations affected the number but not the location of lead phosphate deposits, which appeared at discrete sites along the inner side of the cytoplasmic membrane. Control cells incubated in histochemical mixtures lacking substrate, lead, or both exhibited no lead phosphate depositis. The histochemical localization at membrane sites correlated well with biochemical localization data, which indicated that greater than 80% of the APase activity was associated with the membrane fraction in logarithmically growing cells.

Subunits of the alkaline phosphatase of Bacillus licheniformis: chemical, physicochemical, and dissociation studies

The alkaline phosphatase (orthophosphoric monoester phosphydrolase, EC 3.1.3.1) of Bacillus licheniformis MC14 was studied in an attempt to determine the number of subunits contained in the 120,000-molecular-weight native enzyme. Two moles of arginine was liberated per mole of native enzyme by carboxypeptidases A and B in the presence of sodium dodecyl sulfate. The effect on the native enzyme of progressively lowering the solvent buffer pH was monitored by determining the molecular weight by sedimentation equilibrium analysis, the sedimentation coefficient, the frictional coefficient, and the percent alpha-helix content of the enzyme. The alkaline phosphatase dissociates into two subunits around pH 4. At pH 2.8 a further decrease in S value, but no change in molecular weight, is observed, indicating a change in conformation. The frictional coefficients and percent alpha-helix content agree with this interpretation. A subunit molecular weight of 59,000 was calculated from sodium dodecyl sulfate gels.