Characterization of a recombinant l-rhamnose isomerase from Bacillus subtilis and its application on production of l-lyxose and l-mannose

The gene of an l-rhamnose isomerase (RhaA) from Bacillus subtilis was cloned to the pET28a(+) and then expressed in the E. coli ER2566. The expressed enzyme was purified with a specific activity of 3.58 U/mg by His-Trap affinity chromatography. The recombinant enzyme existed as a 194 kDa tetramer and the maximal activity was observed at pH 8.0 and 60°C. The RhaA displayed activity for l-rhamnose, l-lyxose, l-mannose, d-allose, d-gulose, d-ribose, and l-talose, among all aldopentoses and aldohexoses and it showed enzyme activity for l-form monosaccharides such as l-rhamnose, l-lyxose, l-mannose, and l-talose. The catalytic efficiency (k _cat/K _m) of the recombinant enzyme for l-rhamnose, l-lyxose, and l-mannose were 7,460, 1,013, and 258 M/sec. When l-xylulose 100 g/L and l-fructose 100 g/L were used as substrates, the optimum concentrations of RpiB were determined with 6 and 15 U/mL, respectively. The l-lyxose 40 g/L was produced from l-xylulose 100 g/L by the enzyme during 60 min, while l-mannose 25 g/L was produced from l-fructose 100 g/L for 80 min. The results suggest that RhaA from B. subtilis is a potential producer of l-form monosaccharides.     

Enantioselective N-acetylation of 2-phenylglycine by an unusual N-acetyltransferase from Chryseobacterium sp.

The demand for d-2-phenylglycine used to synthesize semisynthetic antibiotics and pesticides is increasing. We have isolated a Chryseobacterium sp. that selectively transformed the l-form of racemic d,l-2-phenylglycine to (2S)-2-acetylamide-2-phenylacetic acid with a molar yield of 50 % and an enantiomer excess of >99.5 % under optimal culture conditions, consequently resulting in 99 % pure d-2-phenylglycine remaining in the culture. The enantioselective N-acetylation was catalyzed by an acetyl-CoA-dependent N-acetyltransferase whose synthesis was induced by l-2-phenylglycine. The enzyme differed from previously reported bacterial arylamine N-acetyltransferases in molecular mass and substrate specificity. The relative activity ratio of the enzyme with the substrates l-2-phenylglycine, d-2-phenylglycine, 2-(2-chlorophenyl)glycine, and 5-aminosalicylic acid (a good substrate of arylamine N-acetyltransferase) was 100:0:56.9:5.49, respectively. The biotransformation by the N-acetyltransferase-producing bacterium reported here could constitute a new preparative route for the enzymatic resolution of d,l-2-phenylglycine.     

The Synthesis of l-dopa-l-Tyr and The Interaction of l-dopa-l-Tyr With ctDNA

l-dopa-l-Tyr was synthesized by Fmoc solid-phase peptide synthesis, purified by reversed-phase HPLC and characterized by using ¹H, ¹³C NMR and ESI–MS analyses. The interaction of l-dopa-l-Tyr and l-dopa with ctDNA has been investigated respectively by UV–vis absorption and fluorescence spectroscopy. The results showed that both l-dopa and l-dopa-l-Tyr interacted with ctDNA through intercalative mode and l-dopa-l-Tyr showed a higher affinity for DNA. Meanwhile, compared with the free l-dopa, gel electrophoresis assay also demonstrated that l-dopa-l-Tyr interacted with DNA by intercalation.     

l-Arabinose/d-galactose 1-dehydrogenase of Rhizobium leguminosarum bv. trifolii characterised and applied for bioconversion of l-arabinose to l-arabonate with Saccharomyces cerevisiae

Four potential dehydrogenases identified through literature and bioinformatic searches were tested for l-arabonate production from l-arabinose in the yeast Saccharomyces cerevisiae. The most efficient enzyme, annotated as a d-galactose 1-dehydrogenase from the pea root nodule bacterium Rhizobium leguminosarum bv. trifolii, was purified from S. cerevisiae as a homodimeric protein and characterised. We named the enzyme as a l-arabinose/d-galactose 1-dehydrogenase (EC 1.1.1.-), Rl AraDH. It belongs to the Gfo/Idh/MocA protein family, prefers NADP⁺ but uses also NAD⁺ as a cofactor, and showed highest catalytic efficiency (k _cat/K _m) towards l-arabinose, d-galactose and d-fucose. Based on nuclear magnetic resonance (NMR) and modelling studies, the enzyme prefers the α-pyranose form of l-arabinose, and the stable oxidation product detected is l-arabino-1,4-lactone which can, however, open slowly at neutral pH to a linear l-arabonate form. The pH optimum for the enzyme was pH 9, but use of a yeast-in-vivo-like buffer at pH 6.8 indicated that good catalytic efficiency could still be expected in vivo. Expression of the Rl AraDH dehydrogenase in S. cerevisiae, together with the galactose permease Gal2 for l-arabinose uptake, resulted in production of 18 g of l-arabonate per litre, at a rate of 248 mg of l-arabonate per litre per hour, with 86 % of the provided l-arabinose converted to l-arabonate. Expression of a lactonase-encoding gene from Caulobacter crescentus was not necessary for l-arabonate production in yeast.     

Serine racemase: an unconventional enzyme for an unconventional transmitter

The discovery of large amounts of d-serine in the brain challenged the dogma that only l-amino acids are relevant for eukaryotes. The levels of d-serine in the brain are higher than many l-amino acids and account for as much as one-third of l-serine levels. Several studies in the last decades have demonstrated a role of d-serine as an endogenous agonist of N-methyl-d-aspartate receptors (NMDARs). d-Serine is required for NMDAR activity during normal neurotransmission as well as NMDAR overactivation that takes place in neurodegenerative conditions. Still, there are many unanswered questions about d-serine neurobiology, including regulation of its synthesis, release and metabolism. Here, we review the mechanisms of d-serine synthesis by serine racemase and discuss the lessons we can learn from serine racemase knockout mice, focusing on the roles attributed to d-serine and its cellular origin.     

The effect of some environmental factors on the production of L-DOPA by alginate-entrapped cells of Mucuna pruriens

In-vitro-grown cells of Mucuna pruriens, immobilized in calcium-alginate gels, were able to transform the precursor L-tyrosine into L-dihydroxyphenylalanine (L-DOPA). After the immobilization in alginate the plant cells released 90% of the produced L-DOPA into the medium; supplementation of the medium with calcium inhibited both the transformation of L-tyrosine into L-DOPA and the release of L-DOPA into the medium. Continuous illumination of the beads had a slight beneficial effect on the synthesis of L-DOPA. A simple production medium for the transformation of L-tyrosine into L-DOPA was designed. This medium contained only sucrose and sodium chloride as osmotic stabilizers, a low concentration of calcium chloride for stabilization of the alginate beads, and L-tyrosine as the precursor.     

Chromosome counts of some Cuban Angiosperms

Chromosome numbers are reported for 14 species collected in Cuba. The first chromosome records are reported forAlbizzia cubana Britton etWilson (2n=26),Atkinsia cubensis (Britton etWilson)Howard (2n=26),Caesalpinia violacea (Mill.)Standl. (2n=24),Colubrina ferruginosa Brongn. (2n=24). Chromosome numbers of the following species were confirmed:Albizzia lebbeck (L.)Benth. (2n=26),Canavalia maritima (Aubl.)Thouars (2n=22),Casuarina equisetifolia Forst. (2n=18),Cedrela mexicana M.J. Roem. (2n=56),Delonix regia (Bojer)Raf. (2n=28),Guazuma tomentosa H.B.K. (2n=16),Lysiloma bahamense Benth. (2n=26),L. latisiliqua (L.)Benth. (2n=26),Samanea saman (Jacq.)Merrill (2n=26),Thespesia populnea (L.)Soland (2n=26).     

Properties, metabolisms, and applications of l-proline analogues

Due to the unique role of l-proline in the folding and structure of protein, a variety of synthetic proline analogues have been developed. l-Proline analogues have been proven to be valuable reagents for studying cellular metabolism and the regulation of macromolecule synthesis in both prokaryotic and eukaryotic cells. In addition to these fundamental researches, they are useful compounds for industrial use. For instance, microorganisms that overproduce l-proline have been obtained by isolating mutants resistant to l-proline analogues. They are also promising candidates for tuning the biological, pharmaceutical, or physicochemical properties of naturally occurring or de novo designed peptides. Among l-proline analogues, l-azetidine-2-carboxylic acid (l-AZC) is a toxic non-proteinogenic amino acid originally found in lily of the valley plants and trans-4-hydroxy-l-proline (4-l-THOP) is the most abundant component of mammalian collagen. Many hydroxyprolines (HOPs), such as 4-l-THOP and cis-4-hydroxy-l-proline (4-l-CHOP), are useful chiral building blocks for the organic synthesis of pharmaceuticals. In addition, l-AZC and 4-l-CHOP, which are potent inhibitors of cell growth, have been tested for their antitumor activity in tissue culture and in vivo. In this review, we describe the recent discoveries regarding the physiological properties and microbial production and metabolism of l-proline analogues, particularly l-AZC and HOPs. Their applications in fundamental research and industrial use are also discussed.     

Notes on some African hepatic genera 1–5

The present study deals with five genera of hepatics in Africa, Isotachis Mitt., Anastrophyllum (Spruce) Steph., Tritomaria Schiffn. ex Loeske, Gymnocoleopsis (Schust.) Schust. and Lophozia (Dum.) Dum. All African populations of the genus Isotachis Mitt. are considered to be one species, I. aubertii (Schwaegr.) Mitt. Four species of Anastrophyllum (Spruce) Steph. (s.l.), A. auritum (Lehm.) Steph., A. piligerum (Nees) Spruce, A. subcomplicatum (Lehm. et Lindenb.) Steph. and A. minutum (Schreb.) Schust., and two species of Tritomaria Schiffn. et Loeske, T. camerunensis S. Arnell and T. exsecta (Schrad.) Schiffn. ex Loeske occur in Africa. Gymmocoleopsis multiflora (Steph.) Schust. represents a genus and species hitherto unreported for the African flora. Finally, five Lophozia (Dum.) Dum. species, L. argentina (Steph.) Schust., L. capensis S. Arnell, L. decolorans (Limpr.) Steph., L. hedbergii S. Arnell and L. tristaniana (S. Arnell) Váňa, are reported from central and southern Africa; two of these (L. argentina (Steph.) Schust. and L. decolorans (Limpr.) Steph.) represent the first reports from Africa.     

Current knowledge of d-aspartate in glandular tissues

Free d-aspartate (d-Asp) occurs in substantial amounts in glandular tissues. This paper reviews the existing work on d-Asp in vertebrate exocrine and endocrine glands, with emphasis on functional roles. Endogenous d-Asp was detected in salivary glands. High d-Asp levels in the parotid gland during development suggest an involvement of the amino acid in the regulation of early developmental phases and/or differentiation processes. d-Asp has a prominent role in the Harderian gland, where it elicits exocrine secretion through activation of the ERK1/2 pathway. Interestingly, the increase in NOS activity associated with d-Asp administration in the Harderian gland suggests a potential capability of d-Asp to induce vasodilatation. In mammals, an increase in local concentrations of d-Asp facilitates the secretion of anterior pituitary hormones, i.e., PRL, LH and GH, whereas it inhibits the secretion of POMC/α-MSH from the intermediate pituitary and of oxytocin from the posterior pituitary. d-Asp also acts as a negative regulator for melatonin synthesis in the pineal gland. Further, d-Asp can stereo-specifically modulate the production of sex steroids, thus taking part in the endocrine control of reproductive activity. Although d-Asp receptors remain to be characterized, gene expression of NR1 and NR2 subunits of NMDAr responds to d-Asp in the testis.     

Biosynthesis of ethylene glycol in Escherichia coli

Ethylene glycol (EG) is an important platform chemical with steadily expanding global demand. Its commercial production is currently limited to fossil resources; no biosynthesis route has been delineated. Herein, a biosynthesis route for EG production from d-xylose is reported. This route consists of four steps: d-xylose?→?d-xylonate?→?2-dehydro-3-deoxy-d-pentonate?→?glycoaldehyde?→?EG. Respective enzymes, d-xylose dehydrogenase, d-xylonate dehydratase, 2-dehydro-3-deoxy-d-pentonate aldolase, and glycoaldehyde reductase, were assembled. The route was implemented in a metabolically engineered Escherichia coli, in which the d-xylose?→?d-xylulose reaction was prevented by disrupting the d-xylose isomerase gene. The most efficient construct produced 11.7 g?L^?1 of EG from 40.0 g?L^?1 of d-xylose. Glycolate is a carbon-competing by-product during EG production in E. coli; blockage of glycoaldehyde?→?glycolate reaction was also performed by disrupting the gene encoding aldehyde dehydrogenase, but from this approach, EG productivity was not improved but rather led to d-xylonate accumulation. To channel more carbon flux towards EG than the glycolate pathway, further systematic metabolic engineering and fermentation optimization studies are still required to improve EG productivity.     

The human L-pipecolic acid oxidase is similar to bacterial monomeric sarcosine oxidases rather than D-amino acid oxidases

L-Pipecolic acid oxidase activity is deficient in patients with peroxisome biogenesis disorders (PBDs). Because its role, if any, in these disorders is unknown, the authors cloned the human gene to order to further study its functions. BLAST search of the translated sequence showed greatest homology to Bacillus sp. NS-129 monomeric sarcosine oxidase. The purified enzyme could use either L-pipecolic acid or sarcosine as a substrate. No homology was found to the peroxisomal D-amino acid oxidases. A further comparison of L-pipecolic acid oxidase to the two D-amino acid oxidases in peroxisomes showed that the proteins differed in many ways. First, both D-amino acid oxidase and L-pipecolic acid oxidase showed no enzyme activity in liver from Zell-weger syndrome patients; D-aspartate oxidase activity was unchanged from control levels. Although all were targeted to peroxisomes, their targeting signals differed. No L-pipecolic acid oxidase was found in brain or other tissues outside of liver and kidney. The D-amino acid oxidases were similarly and more widely distributed. Finally, although D-amino acid degradation is limited to peroxisomes in mammals, L-pipecolic acid can be oxidized in either mitochondria or peroxisomes, or both.     

Characterization of a recombinant l-fucose isomerase from Caldicellulosiruptor saccharolyticus that isomerizes l-fucose, d-arabinose, d-altrose, and l-galactose

A recombinant l-fucose isomerase from Caldicellulosiruptor saccharolyticus was purified as a single 68 kDa band with an activity of 76 U mg^?1. The molecular mass of the native enzyme was 204 kDa as a trimer. The maximum activity for l-fucose isomerization was at pH 7 and 75°C in the presence of 1 mM Mn²⁺. Its half-life at 70°C was 6.1 h. For aldose substrates, the enzyme displayed activity in decreasing order for l-fucose, with a k _cat of 11,910 min^?1 and a K _m of 140 mM, d-arabinose, d-altrose, and l-galactose. These aldoses were converted to the ketoses l-fuculose, d-ribulose, d-psicose, and l-tagatose, respectively, with 24, 24, 85, 55% conversion yields after 3 h.     

Improved Protease Stability of the Antimicrobial Peptide Pin2 Substituted with d-Amino Acids

Cationic antimicrobial peptides (AMPs) have attracted a great interest as novel class of antibiotics that might help in the treatment of infectious diseases caused by pathogenic bacteria. However, some AMPs with high antimicrobial activities are also highly hemolytic and subject to proteolytic degradation from human and bacterial proteases that limit their pharmaceutical uses. In this work a d-diastereomer of Pandinin 2, d-Pin2, was constructed to observe if it maintained antimicrobial activity in the same range as the parental one, but with the purpose of reducing its hemolytic activity to human erythrocytes and improving its ability to resist proteolytic cleavage. Although, the hydrophobic and secondary structure characteristics of l- and d-Pin2 were to some extent similar, an important reduction in d-Pin2 hemolytic activity (30–40 %) was achieved compared to that of l-Pin2 over human erythrocytes. Furthermore, d-Pin2 had an antimicrobial activity with a MIC value of 12.5 μM towards Staphylococcus aureus, Escherichia coli, Streptococcus agalactiae and two strains of Pseudomonas aeruginosa in agar diffusion assays, but it was half less potent than that of l-Pin2. Nevertheless, the antimicrobial activity of d-Pin2 was equally effective as that of l-Pin2 in microdilution assays. Yet, when d- and l-Pin2 were incubated with trypsin, elastase and whole human serum, only d-Pin2 kept its antimicrobial activity towards all bacteria, but in diluted human serum, l- and d-Pin2 maintained similar peptide stability. Finally, when l- and d-Pin2 were incubated with proteases from P. aeruginosa DFU3 culture, a clinical isolated strain, d-Pin2 kept its antibiotic activity while l-Pin2 was not effective.     

Chromosome numbers in selectedHieracium species in the Krkonoše Mts. (the West Sudeten)

Chromosome numbers are given of 15 species of the genusHieracium L. s. str., representing seven species groups (in the sense of Flora Europaea, roughly corresponding to Zahn's “species principales”) from the Krkono?e Mts., N. Bohemia and SW Poland. For the first time chromosome numbers are reported forH. melanocephalum Tausch (2n=27),H. tubulosum Tausch (2n=36),H. schustleri Zlatník (2n=36),H. fritzei F. Schultz (2n=27),H. rohlenae Zlatník (2n=27),H. nigrescens Willd. (2n=36),H. decipiens Tausch (2n=36),H. atrellum Juxip inSchischkin etBobrov (2n=27),H. subnigrescens (Fries exNorrlin)Dahlst. (2n=36),H. sudeticum Sternberg (2n=36),H. pedunculare Tausch (2n=36),H. glandulosodentatum Uechtr. (2n=36),H. wimmeri Uechtr. (2n=27). InHieracium alpinum L. s. str. the number 2n=27 has been confirmed. The results show a high proportion of tetraploid taxa; no diploids have been found.     

Direct synthesis of polypeptides

Following the procedure of Schramm for the synthesis of polynucleotides and polysaccharides, homopolymers ofdl-leucine,dl-phenylalanine,dl-serine, anddl-valine have been prepared in yields of 13 to 57 % through the mediation of a polymetaphosphate ester. Copolymers of the amino acids also have been prepared in lower yields (4–5 %). Infrared spectra show that the polymers are not diketopiperazines and that the polymers ofdl-leucine,dl-phenylalanine, anddl-valine are polypeptides. Conversions of as much as 57% and degrees of polymerization of approximately 12 were obtained for polyleucine. Small peptides containing possibly 2 to 3 leucine residues were detected and isolated as possible intermediates in the leucine polymerization reaction. For the polymerization ofdl-valine, a temperature of 60°C, a reaction time of 10–24 h, and a ratio of polymetaphosphate ester to amino acid of 3:1 appeared to give the best results. The Schramm procedure was initially suggested as a chemical evolution model for the formation of biological polymers under prebiotic conditions. Although the significance of this reaction to prebiological organic chemistry may be questioned, it still offers a mechanistic model for the study of the synthetic reactions involving polyphosphates which are indirectly relevant to abiotic molecular evolution and the problem of the origin of life.     

Properties of the sugar carrier in Baker's yeast

Incubation ofSaccharomyces cerevisiae cells withd-galactose induced the formation of galactose-utilizing enzymes, among them a monosaccharide carrier, apparently synthesized as a proteinde novo. The synthesis of the carrier preceded that of galactokinase by as much as 2 h. The inducible carrier shows a preference for monosaccharides with an axial hydroxyl group at carbon 4 of theC1 chair conformation or at carbon 2 of the1C chair conformation. Through its mediation, some sugars normally poorly transported (d-galactose,d-fucose,l-xylose,l-arabinose) can enter into the entire cell water, occupying then one more kinetic (and morphological ?) compartment than before induction. Some other monosaccharides, readily transported even by a constitutive carrier system (e.g.l-sorbose,d-xylose,d-arabinose) share the newly synthesized carrier.     

Annotated chromosome numbers of selected asiaticPotentilla species

Chromosome numbers are reported for 19 collections representing 16 AsiaticPotentilla taxa. The first chromosome records are reported forP. desertorum Bunge var.arnavatensis Wolf (2n=28),P. festiva Soják (2n=28),P. griffithii Hook f. subsp.beauvaisii (Cardot) Soják (2n=42),P. micropetala D. Don subsp.byssitecta (Soják) Měsí?ek etSoják (2n=14),P. mollissima Lehm. (2n=28),P. moorcroftii Wall. exLehm. (2n=42),P. multicaulis Bunge (2n=14),P. [x]omissa Soják (2n=35, 56, 70) andP. stanjukoviczii Ovcz. exKoczk. (2n=14). Counts differing from those previously recorded are given forP. algida Soják (2n=56) andP. flagellaris Willd. exSchlecht. (2n=42). Chromosome numbers of the following species were confirmed:P. [x]agrimonioides Bieb. (2n=42),P. chinensis Ser. in DC. (2n=14),P. fragarioides L. (2n=14),P. lineata Trev. (2n=14) andP. sericea L. (2n=28). Taxonomy is briefly discussed. A new combinationP. micropetala D. Don subsp.byssitecta (Soják) Měsí?ek etSoják stat. nov. is proposed.     

Structure–function relationships in human d-amino acid oxidase

Since d-amino acids were identified in mammals, d-serine has been one of the most extensively studied “unnatural amino acids”. This brain-enriched transmitter-like molecule plays a pivotal role in the human central nervous system by modulating the activity of NMDA receptors. Physiological levels of d-serine are required for normal brain development and function; thus, any alterations in neuromodulator concentrations might result in NMDA receptor dysfunction, which is known to be involved in several pathological conditions, including neurodegeneration(s), epilepsy, schizophrenia, and bipolar disorder. In the brain, the concentration of d-serine stored in cells is defined by the activity of two enzymes: serine racemase (responsible for both the synthesis and degradation) and d-amino acid oxidase (which catalyzes d-serine degradation). Both enzymes emerged recently as new potential therapeutic targets for NMDA receptor-related diseases. In this review we have focused on human d-amino acid oxidase and provide an extensive overview of the biochemical and structural properties of this flavoprotein and their functional significance. Furthermore, we discuss the mechanisms involved in modulating enzyme activity and stability with the aim to substantiate the pivotal role of d-amino acid oxidase in brain d-serine metabolism in physiological and pathological conditions and to highlight its great significance for novel drug design/development.