Cellulose Nanofibrils/Alginates Double-Network Composites: Effects of Interfibrillar Interaction and G/M Ratio of Alginates on Mechanical Performance.

Interfibrillar phases and bonding in cellulose nanofibril (CNF)-based composites are crucial for materials performances. In this study, we investigated the influence of CNF surface characteristics, the guluronic acid/mannuronic acid ratio, and the molecular weight of alginates on the structure, mechanical, and barrier properties of CNF/alginate composite films. Three types of CNFs with varying surface charges and nanofibril dimensions were prepared from wood pulp fibers. The interfacial bonding through calcium ion cross-linking between alginate and carboxylated CNFs (TCNFs) led to significantly enhanced stiffness and strength due to the formation of an interpenetrating double network, compared to composites from alginates and CNFs with native negative or cationic surface charges. Various alginates extracted from Alaria esculenta (AE) and Laminaria hyperborea (LH) were also examined. The TCNF/AE composite, prepared from alginate with a high mannuronic acid proportion and high molecular weight, exhibited a Young's modulus of 20.3 GPa and a tensile strength of 331 MPa under dry conditions and a Young's modulus of 430 MPa and a tensile strength of 9.3 MPa at the wet state. Additionally, the TCNF/AE composite demonstrated protective properties as a barrier coating for fruit, significantly reducing browning of banana peels and weight loss of bananas stored under ambient conditions.

Optimization of FK-506 production in Streptomyces tsukubaensis by modulation of Crp-mediated regulation.

FK-506 is a potent immunosuppressive macrocyclic polyketide with growing pharmaceutical interest, produced by Streptomyces tsukubaensis. However, due to low levels synthesized by the wild-type strain, biotechnological production of FK-506 is rather limited. Optimization strategies to enhance the productivity of S. tsukubaensis by means of genetic engineering have been established. In this work primarily global regulatory aspects with respect to the FK-506 biosynthesis have been investigated with the focus on the global Crp (cAMP receptor protein) regulator. In expression analyses and protein-DNA interaction studies, the role of Crp during FK-506 biosynthesis was elucidated. Overexpression of Crp resulted in two-fold enhancement of FK-506 production in S. tsukubaensis under laboratory conditions. Further optimizations using fermentors proved that the strategy described in this study can be transferred to industrial scale, presenting a new approach for biotechnological FK-506 production. KEY POINTS: • The role of the global Crp (cAMP receptor protein) regulator for FK-506 biosynthesis in S. tsukubaensis was demonstrated • Crp overexpression in S. tsukubaensis was applied as an optimization strategy to enhance FK-506 and FK-520 production resulting in two-fold yield increase.

Penicillium chrysogenum as a fungal factory for feruloyl esterases.

Plant biomass is a promising substrate for biorefinery, as well as a source of bioactive compounds, platform chemicals, and precursors with multiple industrial applications. These applications depend on the hydrolysis of its recalcitrant structure. However, the effective biological degradation of plant cell walls requires several enzymatic groups acting synergistically, and novel enzymes are needed in order to achieve profitable industrial hydrolysis processes. In the present work, a feruloyl esterase (FAE) activity screening of Penicillium spp. strains revealed a promising candidate (Penicillium rubens Wisconsin 54-1255; previously Penicillium chrysogenum), where two FAE-ORFs were identified and subsequently overexpressed. Enzyme extracts were analyzed, confirming the presence of FAE activity in the respective gene products (PrFaeA and PrFaeB). PrFaeB-enriched enzyme extracts were used to determine the FAE activity optima (pH 5.0 and 50-55 °C) and perform proteome analysis by means of MALDI-TOF/TOF mass spectrometry. The studies were completed with the determination of other lignocellulolytic activities, an untargeted metabolite analysis, and upscaled FAE production in stirred tank reactors. The findings described in this work present P. rubens as a promising lignocellulolytic enzyme producer. KEY POINTS: • Two Penicillium rubens ORFs were first confirmed to have feruloyl esterase activity. • Overexpression of the ORFs produced a novel P. rubens strain with improved activity. • The first in-depth proteomic study of a P. rubens lignocellulolytic extract is shown.

Mechanistic Basis for Understanding the Dual Activities of the Bifunctional Azotobacter vinelandii Mannuronan C-5-Epimerase and Alginate Lyase AlgE7.

The structure and functional properties of alginates are dictated by the monomer composition and molecular weight distribution. Mannuronan C-5-epimerases determine the monomer composition by catalyzing the epimerization of ß-d-mannuronic acid (M) residues into α-l-guluronic acid (G) residues. The molecular weight is affected by alginate lyases, which catalyze a ß-elimination mechanism that cleaves alginate chains. The reaction mechanisms for the epimerization and lyase reactions are similar, and some enzymes can perform both reactions. These dualistic enzymes share high sequence identity with mannuronan C-5-epimerases without lyase activity. The mechanism behind their activity and the amino acid residues responsible for it are still unknown. We investigate mechanistic determinants involved in the bifunctional epimerase and lyase activity of AlgE7 from Azotobacter vinelandii. Based on sequence analyses, a range of AlgE7 variants were constructed and subjected to activity assays and product characterization by nuclear magnetic resonance (NMR) spectroscopy. Our results show that calcium promotes lyase activity, whereas NaCl reduces the lyase activity of AlgE7. By using defined polymannuronan (polyM) and polyalternating alginate (polyMG) substrates, the preferred cleavage sites of AlgE7 were found to be M|XM and G|XM, where X can be either M or G. From the study of AlgE7 mutants, R148 was identified as an important residue for the lyase activity, and the point mutant R148G resulted in an enzyme with only epimerase activity. Based on the results obtained in the present study, we suggest a unified catalytic reaction mechanism for both epimerase and lyase activities where H154 functions as the catalytic base and Y149 functions as the catalytic acid. IMPORTANCE Postharvest valorization and upgrading of algal constituents are promising strategies in the development of a sustainable bioeconomy based on algal biomass. In this respect, alginate epimerases and lyases are valuable enzymes for tailoring the functional properties of alginate, a polysaccharide extracted from brown seaweed with numerous applications in food, medicine, and material industries. By providing a better understanding of the catalytic mechanism and of how the two enzyme actions can be altered by changes in reaction conditions, this study opens further applications of bacterial epimerases and lyases in the enzymatic tailoring of alginate polymers.

High-throughput assay for effect screening of amphotericin B and bioactive components on filamentous Candida albicans.

AIMS: The aim of this study was to develop a high-throughput robotic microtiter plate-based screening assay for Candida albicans, optimizing growth conditions to replicate the filamentous biofilm growth found in vivo, and subsequently, to demonstrate the assay by evaluating the effect of nutritional drinks alone and in combination with the antifungal amphotericin B (AmB). METHODS AND RESULTS: Candida albicans cultured in a defined growth medium showed filamentous growth in microcolonies, mimicking the morphology of oral mucosal disease (oral candidiasis). Addition of nutrient drinks containing fruit juices, fish oil and whey protein to the medium resulted in changed morphology and promoted growth as free yeast cells and with weak biofilm structures. Minimum inhibitory concentration of AmB on the biofilms was 0.25 µg ml-1 , and this was eightfold reduced (0.0038 µg ml-1 ) in the presence of the nutritional drinks. CONCLUSIONS: The established assay demonstrated applicability for screening of antifungal and anti-biofilm effects of bioactive substances on C. albicans biofilm with clinically relevant morphology. SIGNIFICANCE AND IMPACT OF THE STUDY: Candida albicans is the causative agent of the majority of fungal infections globally. The filamentous morphology of C. albicans and the ability to form biofilm are traits known to increase virulence and resistance towards antifungals. This study describes the development of a plate-based in vitro screening method mimicking the filamentous morphology of C. albicans found in vivo. The assay established can thus facilitate efficient antifungal drug discovery and development.

Alginate Degradation: Insights Obtained through Characterization of a Thermophilic Exolytic Alginate Lyase.

Enzymatic depolymerization of seaweed polysaccharides is gaining interest for the production of functional oligosaccharides and fermentable sugars. Herein, we describe a thermostable alginate lyase that belongs to polysaccharide lyase family 17 (PL17) and was derived from an Arctic Mid-Ocean Ridge (AMOR) metagenomics data set. This enzyme, AMOR_PL17A, is a thermostable exolytic oligoalginate lyase (EC 4.2.2.26), which can degrade alginate, poly-ß-d-mannuronate, and poly-α-l-guluronate within a broad range of pHs, temperatures, and salinity conditions. Site-directed mutagenesis showed that tyrosine Y251, previously suggested to act as a catalytic acid, indeed is essential for catalysis, whereas mutation of tyrosine Y446, previously proposed to act as a catalytic base, did not affect enzyme activity. The observed reaction products are protonated and deprotonated forms of the 4,5-unsaturated uronic acid monomer, Δ, two hydrates of DEH (4-deoxy-l-erythro-5-hexulosuronate), which are formed after ring opening, and, finally, two epimers of a 5-member hemiketal called 4-deoxy-d-manno-hexulofuranosidonate (DHF), formed through intramolecular cyclization of hydrated DEH. The detection and nuclear magnetic resonance (NMR) assignment of these hemiketals refine our current understanding of alginate degradation.IMPORTANCE The potential markets for seaweed-derived products and seaweed processing technologies are growing, yet commercial enzyme cocktails for complete conversion of seaweed to fermentable sugars are not available. Such an enzyme cocktail would require the catalytic properties of a variety of different enzymes, where fucoidanases, laminarinases, and cellulases together with endo- and exo-acting alginate lyases would be the key enzymes. Here, we present an exo-acting alginate lyase that efficiently produces monomeric sugars from alginate. Since it is only the second characterized exo-acting alginate lyase capable of degrading alginate at a high industrially relevant temperature (≥60°C), this enzyme may be of great biotechnological and industrial interest. In addition, in-depth NMR-based structural elucidation revealed previously undescribed rearrangement products of the unsaturated monomeric sugars generated from exo-acting lyases. The insight provided by the NMR assignment of these products facilitates future assessment of product formation by alginate lyases.

Engineering chitinolytic activity into a cellulose-active lytic polysaccharide monooxygenase provides insights into substrate specificity.

Lytic polysaccharide monooxygenases (LPMOs) catalyze oxidative cleavage of recalcitrant polysaccharides such as cellulose and chitin and play an important role in the enzymatic degradation of biomass. Although it is clear that these monocopper enzymes have extended substrate-binding surfaces for interacting with their fibrous substrates, the structural determinants of LPMO substrate specificity remain largely unknown. To gain additional insight into substrate specificity in LPMOs, here we generated a mutant library of a cellulose-active family AA10 LPMO from Streptomyces coelicolor A3(2) (ScLPMO10C, also known as CelS2) having multiple substitutions at five positions on the substrate-binding surface that we identified by sequence comparisons. Screening of this library using a newly-developed MS-based high-throughput assay helped identify multiple enzyme variants that contained four substitutions and exhibited significant chitinolytic activity and a concomitant decrease in cellulolytic activity. The chitin-active variants became more rapidly inactivated during catalysis than a natural chitin-active AA10 LPMO, an observation likely indicative of suboptimal substrate binding leading to autocatalytic oxidative damage of these variants. These results reveal several structural determinants of LPMO substrate specificity and underpin the notion that productive substrate binding by these enzymes is complex, depending on a multitude of amino acids located on the substrate-binding surface.

Exploiting Mannuronan C-5 Epimerases in Commercial Alginate Production.

Alginates are one of the major polysaccharide constituents of marine brown algae in commercial manufacturing. However, the content and composition of alginates differ according to the distinct parts of these macroalgae and have a direct impact on the concentration of guluronate and subsequent commercial value of the final product. The Azotobacter vinelandii mannuronan C-5 epimerases AlgE1 and AlgE4 were used to determine their potential value in tailoring the production of high guluronate low-molecular-weight alginates from two sources of high mannuronic acid alginates, the naturally occurring harvested brown algae (Ascophyllum nodosum, Durvillea potatorum, Laminaria hyperborea and Lessonia nigrescens) and a pure mannuronic acid alginate derived from fermented production of the mutant strain of Pseudomonas fluorescens NCIMB 10,525. The mannuronan C-5 epimerases used in this study increased the content of guluronate from 32% up to 81% in both the harvested seaweed and bacterial fermented alginate sources. The guluronate-rich alginate oligomers subsequently derived from these two different sources showed structural identity as determined by proton nuclear magnetic resonance (1H NMR), high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and size-exclusion chromatography with online multi-angle static laser light scattering (SEC-MALS). Functional identity was determined by minimum inhibitory concentration (MIC) assays with selected bacteria and antibiotics using the previously documented low-molecular-weight guluronate enriched alginate OligoG CF-5/20 as a comparator. The alginates produced using either source showed similar antibiotic potentiation effects to the drug candidate OligoG CF-5/20 currently in development as a mucolytic and anti-biofilm agent. These findings clearly illustrate the value of using epimerases to provide an alternative production route for novel low-molecular-weight alginates.

Biosynthesis and Function of Long Guluronic Acid-Blocks in Alginate Produced by Azotobacter vinelandii.

With the present accessibility of algal raw material, microbial alginates as a source for strong gelling material are evaluated as an alternative for advanced applications. Recently, we have shown that alginate from algal sources all contain a fraction of very long G-blocks (VLG), that is, consecutive sequences of guluronic acid (G) residues of more than 100 residues. By comparing the gelling properties of these materials with in vitro epimerized polymannuronic acid (poly-M) with shorter G-blocks, but comparable with the G-content, we could demonstrate that VLG have a large influence on gelling properties. Hypothesized to function as reinforcement bars, VLG prevents the contraction of the gels during formation (syneresis) and increases the Young's modulus (strength of the gel). Here we report that these VLG structures are also present in alginates from Azotobacter vinelandii and that these polymers consequently form stable, low syneretic gels with calcium, comparable in mechanical strength to algal alginates with the similar monomeric composition. The bacterium expresses seven different extracellular mannuronan epimerases (AlgE1-AlgE7), of which only the bifunctional epimerase AlgE1 seems to be able to generate the long G-blocks when acting on poly-M. The data implies evidence for a processive mode of action and the necessity of two catalytic sites to obtain the observed epimerization pattern. Furthermore, poly-M epimerized with AlgE1 in vitro form gels with comparable or higher rigidity and gel strength than gels made from brown seaweed alginate with matching G-content. These findings strengthen the viability of commercial alginate production from microbial sources.

Chitosan as a Wound Dressing Starting Material: Antimicrobial Properties and Mode of Action.

Fighting bacterial resistance is one of the concerns in modern days, as antibiotics remain the main resource of bacterial control. Data shows that for every antibiotic developed, there is a microorganism that becomes resistant to it. Natural polymers, as the source of antibacterial agents, offer a new way to fight bacterial infection. The advantage over conventional synthetic antibiotics is that natural antimicrobial agents are biocompatible, non-toxic, and inexpensive. Chitosan is one of the natural polymers that represent a very promising source for the development of antimicrobial agents. In addition, chitosan is biodegradable, non-toxic, and most importantly, promotes wound healing, features that makes it suitable as a starting material for wound dressings. This paper reviews the antimicrobial properties of chitosan and describes the mechanisms of action toward microbial cells as well as the interactions with mammalian cells in terms of wound healing process. Finally, the applications of chitosan as a wound-dressing material are discussed along with the current status of chitosan-based wound dressings existing on the market.

Identification of genes affecting alginate biosynthesis in Pseudomonas fluorescens by screening a transposon insertion library.

BACKGROUND: Polysaccharides often are necessary components of bacterial biofilms and capsules. Production of these biopolymers constitutes a drain on key components in the central carbon metabolism, but so far little is known concerning if and how the cells divide their resources between cell growth and production of exopolysaccharides. Alginate is an industrially important linear polysaccharide synthesized from fructose 6-phosphate by several bacterial species. The aim of this study was to identify genes that are necessary for obtaining a normal level of alginate production in alginate-producing Pseudomonas fluorescens. RESULTS: Polysaccharide biosynthesis is costly, since it utilizes nucleotide sugars and sequesters carbon. Consequently, transcription of the genes necessary for polysaccharide biosynthesis is usually tightly regulated. In this study we used an engineered P. fluorescens SBW25 derivative where all genes encoding the proteins needed for biosynthesis of alginate from fructose 6-phosphate and export of the polymer are expressed from inducible Pm promoters. In this way we would avoid identification of genes merely involved in regulating the expression of the alginate biosynthetic genes. The engineered strain was subjected to random transposon mutagenesis and a library of about 11500 mutants was screened for strains with altered alginate production. Identified inactivated genes were mainly found to encode proteins involved in metabolic pathways related to uptake and utilization of carbon, nitrogen and phosphor sources, biosynthesis of purine and tryptophan and peptidoglycan recycling. CONCLUSIONS: The majority of the identified mutants resulted in diminished alginate biosynthesis while cell yield in most cases were less affected. In some cases, however, a higher final cell yield were measured. The data indicate that when the supplies of fructose 6-phosphate or GTP are diminished, less alginate is produced. This should be taken into account when bacterial strains are designed for industrial polysaccharide production.

Cytotoxicity of Poly(Alkyl Cyanoacrylate) Nanoparticles.

Although nanotoxicology has become a large research field, assessment of cytotoxicity is often reduced to analysis of one cell line only. Cytotoxicity of nanoparticles is complex and should, preferentially, be evaluated in several cell lines with different methods and on multiple nanoparticle batches. Here we report the toxicity of poly(alkyl cyanoacrylate) nanoparticles in 12 different cell lines after synthesizing and analyzing 19 different nanoparticle batches and report that large variations were obtained when using different cell lines or various toxicity assays. Surprisingly, we found that nanoparticles with intermediate degradation rates were less toxic than particles that were degraded faster or more slowly in a cell-free system. The toxicity did not vary significantly with either the three different combinations of polyethylene glycol surfactants or with particle size (range 100-200 nm). No acute pro- or anti-inflammatory activity on cells in whole blood was observed.

The effect of the carbohydrate binding module on substrate degradation by the human chitotriosidase.

Human chitotriosidase (HCHT) is one of two active glycoside hydrolase family 18 chitinases produced by humans. The enzyme is associated with several diseases and is thought to play a role in the anti-parasite responses of the innate immune system. HCHT occurs in two isoforms, one 50 kDa (HCHT50) and one 39 kDa variant (HCHT39). Common for both isoforms is a catalytic domain with the (ß/α)8 TIM barrel fold. HCHT50 has an additional linker-region, followed by a C-terminal carbohydrate-binding module (CBM) classified as CBM family 14 in the CAZy database. To gain further insight into enzyme functionality and especially the effect of the CBM, we expressed both isoforms and compared their catalytic properties on chitin and high molecular weight chitosans. HCHT50 degrades chitin faster than HCHT39 and much more efficiently. Interestingly, both HCHT50 and HCHT39 show biphasic kinetics on chitosan degradation where HCHT50 is faster initially and HCHT39 is faster in the second phase. Moreover, HCHT50 produces distinctly different oligomer distributions than HCHT39. This is likely due to increased transglycosylation activity for HCHT50 due the CBM extending the positive subsites binding surface and therefore promoting transglycosylation. Finally, studies with both chitin and chitosan showed that both isoforms have a similarly low degree of processivity. Combining functional and structural features of the two isoforms, it seems that HCHT combines features of exo-processive and endo-nonprocessive chitinases with the somewhat unusual CBM14 to reach a high degree of efficiency, in line with its alleged physiological task of being a "complete" chitinolytic machinery by itself.

New Deferoxamine Glycoconjugates Produced upon Overexpression of Pathway-Specific Regulatory Gene in the Marine Sponge-Derived Streptomyces albus PVA94-07.

Activation of silent biosynthetic gene clusters in Streptomyces bacteria via overexpression of cluster-specific regulatory genes is a promising strategy for the discovery of novel bioactive secondary metabolites. This approach was used in an attempt to activate a cryptic gene cluster in a marine sponge-derived Streptomyces albus PVA94-07 presumably governing the biosynthesis of peptide-based secondary metabolites. While no new peptide-based metabolites were detected in the recombinant strain, it was shown to produce at least four new analogues of deferoxamine with additional acyl and sugar moieties, for which chemical structures were fully elucidated. Biological activity tests of two of the new deferoxamine analogues revealed weak activity against Escherichia coli. The gene knockout experiment in the gene cluster targeted for activation, as well as overexpression of certain genes from this cluster did not have an effect on the production of these compounds by the strain overexpressing the regulator. It seems plausible that the production of such compounds is a response to stress imposed by the production of an as-yet unidentified metabolite specified by the cryptic cluster.

Anti-microbial and cytotoxic 1,6-dihydroxyphenazine-5,10-dioxide (iodinin) produced by Streptosporangium sp. DSM 45942 isolated from the fjord sediment.

Phenazine natural products/compounds possess a range of biological activities, including anti-microbial and cytotoxic, making them valuable starting materials for drug development in several therapeutic areas. These compounds are biosynthesized almost exclusively by eubacteria of both terrestrial and marine origins from erythrose 4-phosphate and phosphoenol pyruvate via the shikimate pathway. In this paper, we report isolation of actinomycete bacteria from marine sediment collected in the Trondheimfjord, Norway. Screening of the isolates for biological activity produced several "hits", one of which was followed up by identification and purification of the active compound from the actinomycete bacterium Streptosporangium sp. The purified compound, identified as 1,6-dihydroxyphenazine-5,10-dioxide (iodinin), was subjected to extended tests for biological activity against bacteria, fungi and mammalian cells. In these tests, the iodinin demonstrated high anti-microbial and cytotoxic activity, and was particularly potent against leukaemia cell lines. This is the first report on the isolation of iodinin from a marine-derived Streptosporangium.

In-process epimerisation of alginates from Saccharina latissima, Alaria esculenta and Laminaria hyperborea.

Alginates are valued in many industries, due to their versatile properties. These polysaccharides originate from brown algae (Phaeophyceae) and some bacteria of the Azotobacter and Pseudomonas genera, consisting of 1 â†’ 4 linked ß-d-mannuronic acid (M), and its C5-epimer α-l-guluronic acid (G). Several applications rely on a high G-content, which confers good gelling properties. Because of its high natural G-content (FG = 0.60-0.75), the alginate from Laminaria hyperborea (LH) has sustained a thriving industry in Norway. Alginates from other sources can be upgraded with mannuronan C-5 epimerases that convert M to G, and this has been demonstrated in many studies, but not applied in the seaweed industry. The present study demonstrates epimerisation directly in the process of alginate extraction from cultivated Saccharina latissima (SL) and Alaria esculenta (AE), and the lamina of LH. Unlike conventional epimerisation, which comprises multiple steps, this in-process protocol can decrease the time and costs necessary for alginate upgrading. In-process epimerisation with AlgE1 enzyme enhanced G-content and hydrogel strength in all examined species, with the greatest effect on SL (FG from 0.44 to 0.76, hydrogel Young's modulus from 22 to 34 kPa). As proof of concept, an upscaled in-process epimerisation of alginate from fresh SL was successfully demonstrated.

Combinatorial mutagenesis and selection of improved signal sequences and their application for high-level production of translocated heterologous proteins in Escherichia coli.

We previously designed the consensus signal peptide (CSP) and demonstrated that it can be used to strongly stimulate heterologous protein production in Escherichia coli. A comparative study using CSP and two bacterial signal sequences, pelB and ompA, showed that the effect of signal sequences on both expression level and translocation efficiency can be highly protein specific. We report here the generation of CSP mutant libraries by a combinatorial mutagenesis approach. Degenerated CSP oligonucleotides were cloned in frame with the 5' end of the bla gene, encoding the mature periplasmic ß-lactamase released from its native signal sequence. This novel design allows for a direct selection of improved signal sequences that positively affect the expression level and/or translocation efficiency of ß-lactamase, based on the ampicillin tolerance level of the E. coli host cells. By using this strategy, 61 different CSP mutants with up to 8-fold-increased ampicillin tolerance level and up to 5.5-fold-increased ß-lactamase expression level were isolated and characterized genetically. A subset of the CSP mutants was then tested with the alternative reporter gene phoA, encoding periplasmic alkaline phosphatase (AP), resulting in an up to 8-fold-increased production level of active AP protein in E. coli. Moreover, it was demonstrated that the CSP mutants can improve the production of the medically important human interferon α2b under high-cell-density cultivations. Our results show that there is a clear potential for improving bacterial signal sequences by using combinatorial mutagenesis, and bioinformatics analyses indicated that the beneficial mutations could not be rationally predicted.

Mannuronan C-5 epimerases suited for tailoring of specific alginate structures obtained by high-throughput screening of an epimerase mutant library.

The polysaccharide alginate is produced by brown algae and some bacteria and is composed of the two monomers, ß-D-mannuronic acid (M) and α-L-guluronic acid (G). The distribution and composition of M/G are important for the chemical-physical properties of alginate and result from the activity of a family of mannuronan C-5 epimerases that converts M to G in the initially synthesized polyM. Traditionally, G-rich alginates are commercially most interesting due to gelling and viscosifying properties. From a library of mutant epimerases we have isolated enzymes that introduce a high level of G-blocks in polyM more efficiently than the wild-type enzymes from Azotobacter vinelandii when employed for in vitro epimerization reactions. This was achieved by developing a high-throughput screening method to discriminate between different alginate structures. Furthermore, genetic and biochemical analyses of the mutant enzymes have revealed structural features that are important for the differences in epimerization pattern found for the various epimerases.

Iodinin (1,6-dihydroxyphenazine 5,10-dioxide) from Streptosporangium sp. induces apoptosis selectively in myeloid leukemia cell lines and patient cells.

Despite recent improvement in therapy, acute myeloid leukemia (AML) is still associated with high lethality. In the presented study, we analyzed the bioactive compound iodinin (1,6-dihydroxyphenazine 5,10-dioxide) from a marine actinomycetes bacterium for the ability to induce cell death in a range of cell types. Iodinin showed selective toxicity to AML and acute promyelocytic (APL) leukemia cells, with EC50 values for cell death up to 40 times lower for leukemia cells when compared with normal cells. Iodinin also successfully induced cell death in patient-derived leukemia cells or cell lines with features associated with poor prognostic such as FLT3 internal tandem duplications or mutated/deficient p53. The cell death had typical apoptotic morphology, and activation of apoptotic signaling proteins like caspase-3. Molecular modeling suggested that iodinin could intercalate between bases in the DNA in a way similar to the anti-cancer drug daunorubicin (DNR), causing DNA-strand breaks. Iodinin induced apoptosis in several therapy-resistant AML-patient blasts, but to a low degree in peripheral blood leukocytes, and in contrast to DNR, not in rat cardiomyoblasts. The low activity towards normal cell types that are usually affected by anti-leukemia therapy suggests that iodinin and related compounds represent promising structures in the development of anti-cancer therapy.

Mannuronate C-5 epimerases and their use in alginate modification.

Alginate is a polysaccharide consisting of ß-D-mannuronate (M) and α-L-guluronate (G) produced by brown algae and some bacterial species. Alginate has a wide range of industrial and pharmaceutical applications, owing mainly to its gelling and viscosifying properties. Alginates with high G content are considered more valuable since the G residues can form hydrogels with divalent cations. Alginates are modified by lyases, acetylases, and epimerases. Alginate lyases are produced by alginate-producing organisms and by organisms that use alginate as a carbon source. Acetylation protects alginate from lyases and epimerases. Following biosynthesis, alginate C-5 epimerases convert M to G residues at the polymer level. Alginate epimerases have been found in brown algae and alginate-producing bacteria, predominantly Azotobacter and Pseudomonas species. The best characterised epimerases are the extracellular family of AlgE1-7 from Azotobacter vinelandii(Av). AlgE1-7 all consist of combinations of one or two catalytic A-modules and one to seven regulatory R-modules, but even though they are sequentially and structurally similar, they create different epimerisation patterns. This makes the AlgE enzymes promising for tailoring of alginates to have the desired properties. The present review describes the current state of knowledge regarding alginate-active enzymes with focus on epimerases, characterisation of the epimerase reaction, and how alginate epimerases can be used in alginate production.