Poly-γ-glutamate from Bacillus subtilis inhibits tyrosinase activity and melanogenesis

Poly-γ-glutamate (γ-PGA) has been considered as one of the most promising biomaterials with a wide range of applications, but there has been no report that directly shows the anti-tyrosinase and anti-melanogenesis properties of γ-PGA. In the present study, we investigated the inhibitory effects of γ- PGA with low molecular weight (Mw; lγ-PGA) and high Mw (hγ-PGA) on mushroom tyrosinase and murine tyrosinase activities and on melanogenesis in B16 melanoma cells. First, we showed that both lγ-PGA and hγ-PGA could effectively inhibit mushroom tyrosinase activities including monophenolase and diphenolase activities in a dose-dependent manner. Second, both lγ-PGA and hγ-PGA showed strong anti-tyrosinase activity and anti-melanogenesis in B16 melanoma cells. Third, both lγ-PGA and hγ-PGA inhibited forskolin-induced tyrosinase activity and melanogenesis by decreasing the levels of intracellular reactive oxygen species and nitric oxide while increasing the catalase activity in B16 cells. This is the first report on the anti-melanogenesis effect of γ-PGA, which suggests that γ-PGA could have a potential in the cosmetic skin whitening business, therapeutic applications and the food industry.

Heterogenous expression of poly-gamma-glutamic acid synthetase complex gene of Bacillus licheniformis WBL-3

Bacillus licheniformis WBL-3, one of poly-gamma-glutamic acid (gamma-PGA) producers, depends on the existence of glutamate in the medium. In this paper, gamma-PGA synthetase complex gene (pgsBCA) was cloned from Bacillus licheniformis WBL-3. pgsBCA gene of B. licheniformis WBL-3 was highly homologous with pgsBCA gene of B. licheniformis 14580. The similarity was 97%, but the similarity of pgsBCA gene between B. licheniformis WBL-3 and Bacillus subtilis IF03336 was only 74%. However, when pgsBCA was expressed in Escherichia coli, the E. coli clone produced gamma-PGA extracellularly. The yield of gamma-PGA was 8.624 g/l. This result infers that B. licheniformis and B. subtilis has the similar gamma-PGA biosynthesis mechanism, namely, glutamic acid is catalyzed by an ATP-dependent amide ligase to synthesize gamma-PGA.

Poly (glutamic acid)--an emerging biopolymer of commercial interest

Poly (γ-glutamic acid) (PGA) is water-soluble, anionic, biodegradable, and edible biopolymer produced by Bacillus subtilis. It has multifarious potential applications in foods, pharmaceuticals, healthcare, water treatment and other fields. The production of PGA has already been established on the industrial scale. Various studies regarding the fermentative production, downstream processing and characterization of PGA have been reported in the literature. This review provides updated information on fermentative production of PGA by various bacterial strains and effect of fermentation conditions and media component on production of PGA in submerged as well as solid state fermentation. Information on the application of genetic engineering for enhancement of yield of PGA, kinetic studies for production of PGA in submerged fermentation and recovery and purification of PGA is included. An attempt has also been made to review the current and potential applications of PGA. This review may contribute to further development of this commercially and academically interesting biopolymer.

Tubulin polyglutamylase enzymes are members of the TTL domain protein family

Polyglutamylation of tubulin has been implicated in several functions of microtubules, but the identification of the responsible enzyme(s) has been challenging. We found that the neuronal tubulin polyglutamylase is a protein complex containing a tubulin tyrosine ligase-like (TTLL) protein, TTLL1. TTLL1 is a member of a large family of proteins with a TTL homology domain, whose members could catalyze ligations of diverse amino acids to tubulins or other substrates. In the model protist Tetrahymena thermophila, two conserved types of polyglutamylases were characterized that differ in substrate preference and subcellular localization.

Synthesis of paucidisperse poly(gamma-benzyl-alpha,L-glutamate) oligomers and star polymers with rigid arms

The synthesis of highly uniform gamma-benzyl-alpha,L-glutamate (BLG) oligomers via a convergent solution phase approach is reported. BLG oligomers were produced with designed lengths of 4, 8, 12, and 16 as a first step to production of BLG-4-mer and BLG-8-mer rod stars. The star oligomers were purified by size-exclusion chromatography and reversed phase HPLC, and characterized by MALDI-TOF mass spectrometry and reversed phase HPLC. These star-shaped BLG oligomers could be used as initiators for growing larger stars.

Efficient recovery of gamma-poly (glutamic acid) from highly viscous culture broth

An efficient strategy for the separation and recovery of gamma-polyglutamic acid (gamma-PGA) from highly viscous broth was developed. This strategy was divided into two processes: The first was to separate gamma-PGA from highly viscous culture broth; the second was to concentrate gamma-PGA solution by ultrafiltration for the reduction of the amount of alcohol required during recovery process with precipitation. By lowering the pH value of culture broth to 3, the viscosity of culture broth and the zeta potential of cell could be reduced to a sixth of the original value at 35 degrees C and a third, respectively. After the acidification of culture broth the energy demand for the separation of gamma-PGA from culture broth by centrifugation could be reduced to 17% of that without it when the centrifugal force was 22,000g. The amount of alcohol required for precipitation could be reduced to a fourth of that generally used without concentration by concentrating 20 g gamma-PGA/L solution to 60 g gamma-PGA/L at pH 5 by ultrafiltration with hollow-fiber membrane cartridge (MWCO 500,000).

[A 90-day subchronic oral toxicity study of Bacillus subtilis gum in F344 rats]

A 90-day subchronic toxicity study of Bacillus subtilis gum was performed in both sexes of F344 rats by feeding of CRF-1 pellet diet containing 0%, 0.18%, 0.55%, 1.66% and 5%. Rats were randomly allocated to 5 groups, each consisting of 10 males and females. No animals died during the administration period and no differences in body weights and food intakes were found among groups of either sex. Kidney weight was significantly increased in both sexes in the groups given concentrations of 1.66% or more. However, the increases of kidney weight were slight in themselves and other data on serum biochemistry and histopathology did not show any apparent toxicological signs including renal toxicity. These findings indicate that the treatment of Bacillus subtilis gum in the diet for 90 days does not exert serious toxicity in rats even at the highest dose.

Isolation of tubulin polyglutamylase from Crithidia; binding to microtubules and tubulin, and glutamylation of mammalian brain alpha- and beta-tubulins

Trypanosomatids have a striking cage-like arrangement of submembraneous microtubules. We previously showed that alpha- and beta- tubulins of these stable microtubules are extensively modified by polyglutamylation. Cytoskeletal microtubular preparations obtained by Triton extraction of Leishmania tarentolae and Crithidia fasciculata retain an enzymatic activity that incorporates radioactive glutamic acid in a Mg2+-ATP-dependent manner into alpha- and beta-tubulins. The tubulin polyglutamylase is extracted by 0.25 M salt. The Crithidia enzyme can be purified by ATP-affinity chromatography, glycerol-gradient centrifugation and ion-exchange chromatography. After extraction from the microtubular cytoskeleton the glutamylase forms a complex with alphabeta tubulin, but behaves after removal of tubulin as a globular protein with a molecular mass of 38x10(3). In highly enriched fractions a corresponding band is the major polypeptide visible in SDS-PAGE. The enzyme from Crithidia recognises mammalian brain tubulin, where it incorporates glutamic acid preferentially into the more acidic variants of both alpha- and beta-tubulins. Synthetic peptides with an oligoglutamyl side chain, corresponding to the carboxy-terminal end of brain alpha- and beta-tubulins, are accepted by the enzyme, albeit at low efficiency. The polyglutamylase elongates the side chain by up to 3 and 5 residues, respectively. Other properties of the tubulin polyglutamylase are also discussed.

Tubulin polyglutamylase: partial purification and enzymatic properties

In this work, we report on a novel enzyme, tubulin polyglutamylase, which catalyzes the posttranslational formation of polyglutamyl side chains onto alpha- and beta-tubulin. The length of the polyglutamyl side chain regulates the interaction between tubulin and various microtubule-associated proteins. We first developed an in vitro glutamylation assay. Activity measured in brain, a tissue particularly enriched with glutamylated tubulin, decreases during postnatal development. Thus, brains from 3-day-old mice were chosen as the starting material, and the enzyme was purified approximately 1000-fold. Its Mr was estimated to be 360K and its sedimentation coefficient 10 s. The enzyme catalyzes the MgATP-dependent addition of l-glutamate onto tubulin subunits. Microtubules are much better substrates than unpolymerized tubulin, and the reaction is very specific for glutamate, other amino acids or glutamate analogues not being substrates. Moreover, glutamyl units are added sequentially onto tubulin, leading to progressive elongation of the polyglutamyl side chains. Side chains of one to six or seven glutamyl units were obtained with microtubules, whereas much longer side chains (up to 15-20 units) were formed with unpolymerized tubulin. Interestingly, such very long polyglutamyl side chains were recently detected in some situations in vivo.

[Separation of methotrexate-polyglutamates by capillary electrophoresis and its application to the measurement of gamma-glutamyl hydrolase activity in human leukemia cells in culture]

We have applied capillary electrophoresis to the separation of methotrexate (MTX)-polyglutamates, and gamma-glutamyl hydrolase (GGH) activities in tumor cells were measured by using this new analytical method. MTX-polyglutamates were sufficiently separated in 15min by capillary electrophoresis with silica fused capillary (phi 50 microns x 75cm), being electrophoresed at 25kV and 30 degrees C in a buffer which contained 20mM sodium tetraborate, 20mM SDS and adjusted pH to 9.5. MTX-polyglutamates eluted were detected at 300nm UV. Cellular extracts obtained from the sensitive and antifolate-resistant human leukemia cell lines, MOLT-3 and K562, were incubated with MTX-glu5 at 37 degrees C for 1, 2 and 4 hr, and the amounts of the degradation products (glu1-glu4) were measured for GGH activity by capillary electrophoresis. There was no significant difference in the production of the metabolites between MOLT-3 and K562 cells (867 +/- 109 vs 799 +/- 56 pmol products/min/1 x 10(7) cells), however, the MTX-resistant MOLT-3 cells with a diminished polyglutamation of folates (MOLT-3/MTX.P-17) and the ZD1694-resistant K562 cells with the impaired membrane transport for reduced folates/MTX/ZD1694 (K562/ZD1694.C) showed decreased activities of GGH (519 +/- 52 and 680 +/- 99 pmol products/min/1 x 10(7) cells, respectively), suggesting the down-regulation of the enzyme in these antifolate-resistant cells concomitant with the intracellular substrate depletion. This study indicates that capillary electrophoresis is a rapid, cost-efficacious method with a sufficient reproducibility in the measurement of GGH activity and must be more suitable for the analysis of clinical samples than HPLC method which requires a large volume of the material.

Experimental and theoretical analysis of the chromatographic behaviour of protein purification fusions carrying charged tails

Poly(glutamic acid) tail consisting of 6 glutamate residues was fused to the N-terminus of Escherichia coli beta-galactosidase (beta-gal), by genetic engineering techniques. The wild-type and modified genes were expressed intracellularly and in soluble state in Escherichia coli, leading to the proteins respectively designated beta-gal2 and E6-beta-gal. Both enzymes were purified by affinity chromatography. The specific activity of purified E6-beta-gal was found to be comparable to the wild-type enzyme and its increased net charge was indicated by lon-Exchange Chromatography (IEC). The use of such a charged fusion for selective recovery of beta-gal from cell extract using IEC and Ion-Exchange Membrane Chromatography (IEMC) was explored. The additional charges enabled the separation factor to be increased about two-fold on both IEC and IEMC, but the IEMC step achieved a better throughput than the IEC step. The selectivity of recovery promoted by the charged tail was further analysed by processing the experimental data obtained in IEC with the Stoichiometric Displacement Model, a recent model very appropriate for the understanding of the retention of polymeric biomolecules on ion-exchangers. It was shown that E6-beta-gal had the same characteristic charge as beta-gal2 but that the binding constant to the ion-exchanger of the tagged beta-gal was 6 times greater than for the wild-type enzyme.

Preparation and properties of A-B-A type block copolymer membranes consisting of poly(N-hydroxypropyl-L-glutamine) as the A component and polyisoprene as the B component

A-B-A type block copolymer (GIG(P)) membranes consisting of poly(N-hydroxypropyl-L-glutamine) (PHPG) as the A component and polyisoprene (PI) as the B component were prepared by carrying out aminoalcoholysis reaction with 3'-amino-1-propanol and a crosslinking reaction with 1,8-octamethylenediamine (OMDA) on membranes of the starting block copolymer (GIG) membranes consisting of poly(gamma-benzyl L-glutamate) (PBLG) and PI. It was shown that the effective crosslink density was proportional to the molar % of OMDA in the reaction mixture. The relation between their bulk structure and membrane properties was investigated, such as the swelling ratio q in a pseudo-extracellular fluid (PECF), tensile properties, and enzymatic degradation behaviour of the membranes in PECF. The tensile properties of the hydrophilic membranes were highly dependent on q in PECF, and on the hydrophobic portions in molecular chains, whose behaviour was typical of an elastomer. Biodegradation of samples in vitro by papain indicated that the rate of degradation was also highly dependent on q of membranes in PECF.

Enzymatic synthesis of folate and antifolate polyglutamates with Escherichia coli folylpolyglutamate synthetase

Escherichia coli folylpolyglutamate synthetase was used to synthesize micromole quantities of polyglutamyl conjugates of folic acid, methotrexate, and other analogs of folic acid. The products of the enzymatic reactions were purified by semipreparative C18 HPLC. The position of each amide linkage (gamma or alpha carboxyl) in the polyglutamated products was determined by limited and exhaustive hydrolyses with hog kidney folylpolyglutamate hydrolase and with yeast carboxypeptidase Y. Under standard reaction conditions, the E. coli enzyme added up to five glutamyl residues to each monoglutamated substrate, primarily at the gamma carboxyl position. Thus, an enzyme which naturally adds only two glutamates to naturally occurring folates can be used synthetically to make higher polyglutamates of a wide range of synthetic substrates. The products of the reactions are valuable tools for the study of the metabolism of antifolate drugs as well as metabolic reactions involving folate cofactors.

The measurement of polyglutamate metabolites of the thymidylate synthase inhibitor, ICI D1694, in mouse and human cultured cells

A method is described for the measurement of the polyglutamates of the quinazoline thymidylate synthase inhibitor, N-(5-[N-(3,4-dihydro-2-methyl-4-oxoquinazolin- 6-ylmethyl)-N-methylamino]-2-theonyl)-L-glutamic acid (ICI D1694). This involved incubation of cells with [5-3H]ICI D1694, extraction of the polyglutamates and their analysis by HPLC using an ion-pairing method. Co-chromatography with ICI D1694 and its synthetic di-hexaglutamate standards (UV detection) aided identification of the [3H]polyglutamates in the fractions recovered from the HPLC. Recovery of the polyglutamates at each stage of extraction and analysis was very good (77-84% overall recovery). Polyglutamates readily accumulated as the tri-, tetra and penta forms and occasionally a small amount of hexaglutamate was found. After mouse L1210 leukemia or human W1L2 lymphoblastoid cells were incubated for 30 min with 0.1 microM [3H]ICI D1694 there was a approximately 6-fold concentration effect intracellularly with most of the 3H associated with polyglutamate forms (approximately 75% and 96% for the L1210 and W1L2, respectively). Even some of the higher chain length tetra- and pentaglutamates could be detected at this time. After 4 hr incubation the total level of intracellular 3H had risen to 2-3 microM, greater than 96% of which was associated with polyglutamates (mainly tetra- and pentaglutamates). Four other human cell lines, two ovarian (CH1 and 41M), the MCF-7 breast and the HT-29 colon, were examined for their ability to form intracellular polyglutamates. A 4 hr incubation with 0.1 microM [3H]ICI D1694 resulted in a substantial intracellular accumulation of the drug (20-100-fold) in its polyglutamate forms with only 2-20% remaining as the parent monoglutamate, depending on the cell line. The major polyglutamate was again cell line dependent, ranging from the tri to the penta form. Prolonging the incubation time to 24 hr allowed a further accumulation of drug with a larger percentage appearing as tri- to hexaglutamates. Although cell lines differed in the total level of polyglutamates formed and the pattern of chain length observed, rapid and extensive polyglutamation of ICI D1694 occurred in all the cell types examined.

Poly(gamma-glutamic acid)s are the major constituents of nematocysts in Hydra (Hydrozoa, Cnidaria)

The 2.80 +/- 0.20 mumol of anions found/mg of isolated and purified dry nematocysts (capsular secretory products of stinging cells) from Hydra make up the majority of the soluble capsular content. They are, in cooperation with corresponding cations, responsible for the generation and regulation of an internal osmotic pressure that amounts up to 150 bar (Weber, J. (1989) Eur. J. Biochem. 184, 465-476). The anions are organized as linear homopolymers of L-glutamic acids which are linked by gamma-carboxyl-alpha-amino amide bonds; the degree of polymerization is heterogeneous and dependent on the particular type of nematocyst. In situ the intracapsular glutamic acid monomer concentration is as high as 2 M. This is the first time that poly(gamma-glutamic acid)s, which are known to occur in some selected bacteria, are reported for eucaryotes. It is suggested that they may also be present as predominant components in nematocysts of other cnidarian species and thus might represent a class of compounds which is characteristic for a whole phylum of the animal kingdom.

Evidence for direct inhibition of de novo purine synthesis in human MCF-7 breast cells as a principal mode of metabolic inhibition by methotrexate

We have investigated the role of dihydrofolate (H2PteGlu) accumulation in the inhibition of de novo purine synthesis by methotrexate (MTX) in human MCF-7 breast cancer cells. Previous studies have shown that cytotoxic concentrations of MTX that inhibit dihydrofolate reductase produce only minimal depletion of the reduced folate cofactor, 10-formyltetrahydrofolate, required for purine synthesis. At the same time, de novo purine synthesis is totally inhibited. In these studies, we show that 10 microM MTX causes inhibition of purine synthesis at the step of phosphoribosylaminoimidazolecarboxamide (AICAR) transformylase, as reflected in a 2-3-fold expansion of the intracellular AICAR pool. The inhibition of purine synthesis coincides with the rapid intracellular accumulation of H2PteGlu, a known inhibitor of AICAR transformylase. When the generation of H2PteGlu is blocked by pretreatment with 50 microM 5-fluorodeoxyuridine (FdUrd), an inhibitor of thymidylate synthase, MTX no longer causes inhibition of purine synthesis. Intermediate levels of H2PteGlu produced in the presence of lower (0.1-10 microM) concentrations of FdUrd led to proportional inhibition of purine biosynthesis, and the exogenous addition of H2PteGlu to breast cells in culture re-established the block in purine synthesis in the presence of FdUrd and MTX. The early phases of inhibition of purine biosynthesis could be ascribed only to H2PteGlu accumulation. MTX polyglutamates, also known to inhibit AICAR transformylase, were present in breast cells only after 6 h of incubation with the parent compounds and were not formed in cells preincubated with FdUrd. The lipid-soluble antifolate trimetrexate, which does not form polyglutamates, produced modest 10-formyltetrahydrofolate depletion, but caused marked H2PteGlu accumulation and a parallel inhibition of purine biosynthesis. This evidence leads to the conclusion that MTX and the lipid-soluble analog trimetrexate cause inhibition of purine biosynthesis through the accumulation of H2PteGlu behind the blocked dihydrofolate reductase reaction.

Methotrexate metabolism in mutant Chinese hamster ovary cells lacking dihydrofolate reductase

To study the influence of the level of dihydrofolate reductase (DHFR) on methotrexate (MTX) metabolism, the formation of methotrexate polyglutamates (MTXPGs) and the retention of the drug were examined in Chinese hamster ovary cells (DUKXB11) lacking DHFR and in control cells (CHO-UTC). Both cells accumulated MTXPGs poorly. After a 24-hr incubation with 1.0 microM [3H]MTX, the level of total MTX in DUKXB11 cells was 40% of that in CHO-UTC cells, reflecting the lack of DHFR-bound MTX and MTXPGs in the mutant cells. MTXPGs accounted for a higher proportion of the intracellular MTX in DUKXB11 than in CHO-UTC cells (25 vs 18%). Following exposure to 3.0 microM MTX for 24 hr, total drug levels were similar in both cell lines, and MTXPGs constituted even more of the intracellular drug in DUKXB11 cells compared to CHO-UTC cells (34 vs 23%). DUKXB11 cells accumulated longer MTXPGs (MTXG1u3,4) compared to CHO-UTC cells (MTXG1u2,3), following exposure to both 1.0 and 3.0 microM MTX. The longer MTXPGs in the mutant cells may have resulted from the lack of DHFR in them. Binding of MTXPGs to DHFR in CHO-UTC may interfere with their further polyglutamylation. When cells were resuspended in drug-free buffer for 1 hr following a 24-hr incubation with MTX, the retention of drug was less in DUKXB11 cells (46%) than in CHO-UTC cells (78%), due mainly to a greater loss of unmetabolized MTX in the mutant cells (89%) than in control cells (26%). Nevertheless, the amount of non-exchangeable unmetabolized MTX retained in DUKXB11 cells following exposure to 3.0 microM MTX exceeded the MTX-binding capacity. These studies demonstrate that DHFR-deficient cells accumulated more and longer MTXPGs than control cells. In addition, they suggest that some unmetabolized MTX was retained in cells not bound to DHFR.

Studies on the in vivo synthesis of methotrexate polyglutamates and their efflux properties in normal, proliferative, and neoplastic mouse tissues

Synthesis of poly-gamma-glutamyl metabolites of methotrexate was demonstrated in mouse small intestine, liver and bone marrow, and in L1210 leukemia, Sarcoma 180 and Ehrlich tumor cells after sc injections of [3H]methotrexate to tumor bearing mice. Ion exchange chromatography of tissue extracts resolved six peaks of radioactivity believed to represent methotrexate and metabolites with up to 4 additional glutamyl residues. Polyglutamate formation in L1210 cells and small intestine was shown to be independent of dose at least to 400 mg/kg as long as intracellular levels of drug in excess of the dihydrofolate reductase binding capacity (exchangeable) were maintained. Both the total amount of polyglutamates and the average length of the polyglutamyl chain increased with time as long as exchangeable level of drug were present intracellularily. The results also showed differences in the extent of metabolism of methotrexate polyglutamates among the tissues examined. Although, these differences were at times very large, there was no consistent correlation between these differences and other pharmacologic parameters or cytoxicity. Tumor cells appeared to synthesize more polyglutamates than the normal tissues examined. However, differences in total drug persistence and sensitivity to drug among tumor cells and among normal tissues did not reflect the relative extent of polyglutamate synthesis in each group. We observed no selective retention of polyglutamates as compared to methotrexate by L1210 cells in vitro as indicated by the extracellular accumulation during efflux of methotrexate and the polyglutamates. This could only be demonstrated by allowing efflux of intracellular drug in the presence of extracellular dihydrofolate reductase, which averted hydrolysis of the polyglutamates. It is concluded that the extent of polyglutamate synthesis per se may not be a determinant of drug sensitivity in murine tissues. However, the accumulation of these metabolites may contribute in some way to overall therapeutic response or relative cytotoxicity.

An inverse relationship of rat liver folate polyglutamate chain length to nutritional folate sufficiency

The relative concentrations of folylpolyglutamates of differing chain length in rat liver and the uptake of exogenous [3H]folic acid (20 microCi, 20 microgram) into liver folylpolyglutamates were examined in rats maintained on (a) standard and folate-supplemented standard diets and (b) semi-defined folate-sufficient and folate-deficient diets. Folylpolyglutamates extracted from liver were cleaved to p-aminobenzoylpolyglutamates which were separated by ion-exchange chromatography. The relative concentrations and ultimate radiolabeling of longer-chain folylpolyglutamates (six, seven and eight glutamate residues) were greatest in the livers of folate-deficient rats, whereas the intermediate-chain folylpolyglutamates (three, four and five glutamate residues) were the greatest portion of total liver folates of folate-supplemented rats. Thus, the length of the polyglutamate chain added to liver folates is inversely related to the total concentration of liver folates. These data suggest that folylpolyglutamate biosynthesis in the liver may be controlled by the liver folate concentrations. In folate insufficiency such a control mechanism would serve to enhance the affinity of folates for folate-dependent enzymes and to conserve the liver folate concentration.