Essential dextrin structure as donor substrate for 4-α-glucanotransferase in glycogen debranching enzyme.

Glycogen debranching enzyme is a single polypeptide with distinct catalytic sites for 4-α-glucanotransferase and amylo-α-1,6-glucosidase. To allow phosphorylase to degrade the inner tiers of highly branched glycogen, 4-α-glucanotransferase converts the phosphorylase-limit biantennary branch G-G-G-G-(G-G-G-G↔)G-G- (G: d-glucose, hyphens: α-1,4-linkages; double-headed arrow: α-1,6-linkage) into the G-G-G-G-(G↔)G-G- residue, which is then subjected to amylo-α-1,6-glucosidase to release the remaining G↔ residue. However, while the essential side-chain structure of the 4-α-glucanotransferase donor substrate has been determined to be the G-G-G-G↔ residue (Watanabe, Y., et al. (2008) J. Biochem.143, 435-440), its essential main-chain structure remains to be investigated. In this study, we probed the 4-α-glucanotransferase donor-binding region using novel fluorogenic dextrins Gm-(G4↔)G-Gn-F (F: 1-deoxy-1-[(2-pyridyl)amino]-d-glucitol) and maltohexaose (G6) as the donor and acceptor substrates, respectively. 4-α-Glucanotransferase exhibited maximum activity towards G4-(G4↔)G-F and G4-(G4↔)G-G-F, indicating that recognition of the G4-(G4↔)G-moiety was essential for full enzyme function. Notably, when the 4-α-glucanotransferase activity towards G4-(G4↔)G-G-F was taken as unity, those towards nonbranching dextrins were < 0.001. This indicated that the disproportionation activities towards maltooligosaccharides (Gm) are abnormal behaviours of 4-α-glucanotransferase. Notably, however, these activities have been traditionally measured to identify the 4-α-glucanotransferase mutations causing glycogen storage disease type III. This study provides a basis for more accurate identification.

Combined resistant dextrin and low-dose Mg oxide administration increases short-chain fatty acid and lactic acid production by gut microbiota.

The consumption of resistant dextrin improves constipation, while its fermentation and degradation by the intestinal microbiota produce short-chain fatty acids (SCFA) and lactic acid, which have beneficial effects on host metabolism and immunity. Mg oxide (MgO) is an important mineral that is used to treat constipation. Therefore, resistant dextrin and MgO are often administered together to improve constipation. However, limited information is available regarding the effect of this combination on SCFA and lactic acid production. Crl:CD1(ICR) mice were fed a Mg-free diet with 5% resistant dextrin, followed by oral administration of MgO. We collected the cecum contents and measured SCFA and lactic acid levels. Additionally, the human subjects received resistant dextrin and Mg supplements as part of their habitual diet. The results of this study demonstrate that intestinal microbiota cannot promote SCFA and lactic acid production in the absence of Mg. In a mouse model, low doses of MgO promoted the production of SCFA and lactic acid, whereas high doses decreased their production. In humans, the combined consumption of resistant dextrin and Mg supplements increased the production of SCFA and lactic acid. The production of SCFA and lactic acid from dietary fiber may be augmented by the presence of MgO.

Slowly digestible property of highly branched α-limit dextrins produced by 4,6-α-glucanotransferase from Streptococcus thermophilus evaluated in vitro and in vivo.

Starch molecules are first degraded to slowly digestible α-limit dextrins (α-LDx) and rapidly hydrolyzable linear malto-oligosaccharides (LMOs) by salivary and pancreatic α-amylases. In this study, we designed a slowly digestible highly branched α-LDx with maximized α-1,6 linkages using 4,6-α-glucanotransferase (4,6-αGT), which creates a short length of α-1,4 side chains with increasing branching points. The results showed that a short length of external chains mainly composed of 1-8 glucosyl units was newly synthesized in different amylose contents of corn starches, and the α-1,6 linkage ratio of branched α-LDx after the chromatographical purification was significantly increased from 4.6% to 22.1%. Both in vitro and in vivo studies confirmed that enzymatically modified α-LDx had improved slowly digestible properties and extended glycemic responses. Therefore, 4,6-αGT treatment enhanced the slowly digestible properties of highly branched α-LDx and promises usefulness as a functional ingredient to attenuate postprandial glucose homeostasis.

Observation of Cellodextrin Accumulation Resulted from Non-Conventional Secretion of Intracellular ß-Glucosidase by Engineered Saccharomyces cerevisiae Fermenting Cellobiose.

Although engineered Saccharomyces cerevisiae fermenting cellobiose is useful for the production of biofuels from cellulosic biomass, cellodextrin accumulation is one of the main problems reducing ethanol yield and productivity in cellobiose fermentation with S. cerevisiae expressing cellodextrin transporter (CDT) and intracellular ß-glucosidase (GH1-1). In this study, we investigated the reason for the cellodextrin accumulation and how to alleviate its formation during cellobiose fermentation using engineered S. cerevisiae fermenting cellobiose. From the series of cellobiose fermentation using S. cerevisiae expressing only GH1-1 under several culture conditions, it was discovered that small amounts of GH1-1 were secreted and cellodextrin was generated through trans-glycosylation activity of the secreted GH1-1. As GH1-1 does not have a secretion signal peptide, non-conventional protein secretion might facilitate the secretion of GH1-1. In cellobiose fermentations with S. cerevisiae expressing only GH1-1, knockout of TLG2 gene involved in non-conventional protein secretion pathway significantly delayed cellodextrin formation by reducing the secretion of GH1-1 by more than 50%. However, in cellobiose fermentations with S. cerevisiae expressing both GH1-1 and CDT-1, TLG2 knockout did not show a significant effect on cellodextrin formation, although secretion of GH1-1 was reduced by more than 40%. These results suggest that the development of new intracellular ß-glucosidase, not influenced by non-conventional protein secretion, is required for better cellobiose fermentation performances of engineered S. cerevisiae fermenting cellobiose.

Modulation of the fecal microbiome and metabolome by resistant dextrin ameliorates hepatic steatosis and mitochondrial abnormalities in mice.

Targeting the gut-liver axis by manipulating the intestinal microbiome is a promising therapy for nonalcoholic fatty liver disease (NAFLD). This study modulated the intestinal microbiota to explore whether resistant dextrin, as a potential prebiotic, could ameliorate high-fat diet (HFD)-induced hepatic steatosis in C57BL/6J mice. After two months of feeding, significant hepatic steatosis with mitochondrial dysfunction was observed in the HFD-fed mice. However, the concentrations of triglycerides and malondialdehyde in liver tissue and the levels of alanine aminotransferase and aspartate aminotransferase in the serum of mice fed an HFD plus resistant dextrin diet (HFID) were significantly decreased compared to the HFD-fed mice. Additionally, hepatic mitochondrial integrity and reactive oxygen species accumulation were improved in HFID-fed mice, ameliorating hepatic steatosis. The fecal microbiome of HFD-fed mice was enriched in Bifidobacterium, Lactobacillus, and Globicatella, while resistant dextrin increased the abundance of Parabacteroides, Blautia, and Dubosiella. Major changes in fecal metabolites were confirmed for HFID-fed mice, including those related to entero-hepatic circulation (i.e., bile acids), tryptophan metabolism (e.g., indole derivatives), and lipid metabolism (e.g., lipoic acid), as well as increased antioxidants including isorhapontigenin. Furthermore, resistant dextrin decreased inflammatory cytokine levels and intestinal permeability and ameliorated intestinal damage. Together, these findings augmented current knowledge on prebiotic treatment for NAFLD.

The Lipomyces starkeyi gene Ls120451 encodes a cellobiose transporter that enables cellobiose fermentation in Saccharomyces cerevisiae.

Processed lignocellulosic biomass is a source of mixed sugars that can be used for microbial fermentation into fuels or higher value products, like chemicals. Previously, the yeast Saccharomyces cerevisiae was engineered to utilize its cellodextrins through the heterologous expression of sugar transporters together with an intracellular expressed ß-glucosidase. In this study, we screened a selection of eight (putative) cellodextrin transporters from different yeast and fungal hosts in order to extend the catalogue of available cellobiose transporters for cellobiose fermentation in S. cerevisiae. We confirmed that several in silico predicted cellodextrin transporters from Aspergillus niger were capable of transporting cellobiose with low affinity. In addition, we found a novel cellobiose transporter from the yeast Lipomyces starkeyi, encoded by the gene Ls120451. This transporter allowed efficient growth on cellobiose, while it also grew on glucose and lactose, but not cellotriose nor cellotetraose. We characterized the transporter more in-depth together with the transporter CdtG from Penicillium oxalicum. CdtG showed to be slightly more efficient in cellobiose consumption than Ls120451 at concentrations below 1.0 g/L. Ls120451 was more efficient in cellobiose consumption at higher concentrations and strains expressing this transporter grew slightly slower, but produced up to 30% more ethanol than CdtG.

Effects of reaction condition on glycosidic linkage structure, physical-chemical properties and in vitro digestibility of pyrodextrins prepared from native waxy maize starch.

Glycosidic linkage structure, physical-chemical properties and in vitro digestibility of pyrodextrins prepared using different reaction conditions were characterized. Intensification of reaction condition promoted starch hydrolysis and transglucosidation until the solubility of pyrodextrin reached 100%. New branch points were formed including α-1,2, ß-1,2, ß-1,4, ß-1,6 and α-1,6 linkages. Majority of the branch points was α-1,6 and ß-1,6 linkages which in together accounted for more than 70% of the total branches. The degree of branching increased at intensified reaction conditions and plateaued at approximately 24%. Exhaustively hydrolyzing pyrodextrin by α-amylase and amyloglucosidase significantly decreased the degree of α-1,4 but not α-1,6 linkages. The retained α-1,4 and α-1,6 linkages were probably protected from enzyme hydrolysis by the non-starch linkages due to steric hindrance. The resistant starch content was positively correlated with the degree of branching of pyrodextrin. The decreased in vitro digestibility of pyrodextrin was attributed to the formation of new glycosidic linkages.

A re-evaluation of diastatic Saccharomyces cerevisiae strains and their role in brewing.

Diastatic strains of Saccharomyces cerevisiae possess the unique ability to hydrolyze and ferment long-chain oligosaccharides like dextrin and starch. They have long been regarded as important spoilage microbes in beer, but recent studies have inspired a re-evaluation of the significance of the group. Rather than being merely wild-yeast contaminants, they are highly specialized, domesticated yeasts belonging to a major brewing yeast lineage. In fact, many diastatic strains have unknowingly been used as production strains for decades. These yeasts are used in the production of traditional beer styles, like saison, but also show potential for creation of new beers with novel chemical and physical properties. Herein, we review results of the most recent studies and provide a detailed account of the structure, regulation, and functional role of the glucoamylase-encoding STA1 gene in relation to brewing and other fermentation industries. The state of the art in detecting diastatic yeast in the brewery is also summarized. In summary, these latest results highlight that having diastatic S. cerevisiae in your brewery is not necessarily a bad thing. KEY POINTS: •Diastatic S. cerevisiae strains are important spoilage microbes in brewery fermentations. •These strains belong to the 'Beer 2' or 'Mosaic beer' brewing yeast lineage. •Diastatic strains have unknowingly been used as production strains in breweries. •The STA1-encoded glucoamylase enables efficient maltotriose use.

Three-Enzyme Phosphorylase Cascade for Integrated Production of Short-Chain Cellodextrins.

Cellodextrins are linear ß-1,4-gluco-oligosaccharides that are soluble in water up to a degree of polymerization (DP) of ≈6. Soluble cellodextrins have promising applications as nutritional ingredients. A DP-controlled, bottom-up synthesis from expedient substrates is desired for their bulk production. Here, a three-enzyme glycoside phosphorylase cascade is developed for the conversion of sucrose and glucose into short-chain (soluble) cellodextrins (DP range 3-6). The cascade reaction involves iterative ß-1,4-glucosylation of glucose from α-glucose 1-phosphate (αGlc1-P) donor that is formed in situ from sucrose and phosphate. With final concentration and yield of the soluble cellodextrins set as targets for biocatalytic synthesis, three major factors of reaction efficiency are identified and partly optimized: the ratio of enzyme activity, the ratio of sucrose and glucose, and the phosphate concentration used. The efficient use of the phosphate/αGlc1-P shuttle for cellodextrin production is demonstrated and the soluble product at 40 g L-1 is obtained under near-complete utilization of the donor substrate offered (88 mol% from 200 mm sucrose). The productivity is 16 g (L h)-1 . Through a simple two-step route, the soluble cellodextrins are recovered from the reaction mixture in ≥95% purity and ≈92% yield. Overall, this study provides the basis for their integrated production.

High level production of flavonoid rhamnosides by metagenome-derived Glycosyltransferase C in Escherichia coli utilizing dextrins of starch as a single carbon source.

Flavonoids exert a wide variety of biological functions that are highly attractive for the pharmaceutical and healthcare industries. However, their application is often limited by low water solubility and poor bioavailability, which can generally be relieved through glycosylation. Glycosyltransferase C (GtfC), a metagenome-derived, bacterial glycosyltransferase, was used to produce novel and rare rhamnosides of various flavonoids, including chrysin, diosmetin, biochanin A, and hesperetin. Some of them are to our knowledge firstly described within this work. In our study we deployed a new metabolic engineering approach to increase the rhamnosylation rate in Escherichia coli whole cell biotransformations. The coupling of maltodextrin metabolism to glycosylation was developed in E. coli MG1655 with the model substrate hesperetin. The process proved to be highly dependent on the availability of maltodextrins. Maximal production was achieved by the deletion of the phosphoglucomutase (pgm) and UTP-glucose-1-phosphate uridyltransferase (galU) genes and simultaneous overexpression of the dTDP-rhamnose synthesis genes (rmlABCD) as well as glucan 1,4-alpha-maltohexaosidase for increased maltodextrin degradation next to GtfC in E. coli UHH_CR5-A. These modifications resulted in a 3.2-fold increase of hesperetin rhamnosides compared to E. coli MG1655 expressing GtfC in 24 h batch fermentations. Furthermore, E. coli UHH-CR_5-A was able to produce a final product titer of 2.4 g/L of hesperetin-3'-O-rhamnoside after 48 h. To show the versatility of the engineered E. coli strain, biotransformations of quercetin and kaempferol were performed, leading to production of 4.3 g/L quercitrin and 1.9 g/L afzelin in a 48 h time period, respectively. So far, these are the highest published yields of flavonoid rhamnosylation using a biotransformation approach. These results clearly demonstrate the high potential of the engineered E. coli production host as a platform for the high level biotransformation of flavonoid rhamnosides.

A deletion in the STA1 promoter determines maltotriose and starch utilization in STA1+ Saccharomyces cerevisiae strains.

Diastatic strains of Saccharomyces cerevisiae are common contaminants in beer fermentations and are capable of producing an extracellular STA1-encoded glucoamylase. Recent studies have revealed variable diastatic ability in strains tested positive for STA1, and here, we elucidate genetic determinants behind this variation. We show that poorly diastatic strains have a 1162-bp deletion in the promoter of STA1. With CRISPR/Cas9-aided reverse engineering, we show that this deletion greatly decreases the ability to grow in beer and consume dextrin, and the expression of STA1. New PCR primers were designed for differentiation of highly and poorly diastatic strains based on the presence of the deletion in the STA1 promoter. In addition, using publically available whole genome sequence data, we show that the STA1 gene is prevalent among the 'Beer 2'/'Mosaic Beer' brewing strains. These strains utilize maltotriose efficiently, but the mechanisms for this have been unknown. By deleting STA1 from a number of highly diastatic strains, we show here that extracellular hydrolysis of maltotriose through STA1 appears to be the dominant mechanism enabling maltotriose use during wort fermentation in STA1+ strains. The formation and retention of STA1 seems to be an alternative evolutionary strategy for efficient utilization of sugars present in brewer's wort. The results of this study allow for the improved reliability of molecular detection methods for diastatic contaminants in beer and can be exploited for strain development where maltotriose use is desired.

In-depth study of the changes in properties and molecular structure of cassava starch during resistant dextrin preparation.

Physical, chemical and thermal properties, as well as molecular structure of cassava-based resistant dextrins prepared under different dextrinization conditions (0.04-0.10% HCl, 100-120 °C, 60-180 min) were determined. Increasing acid concentration, temperature and heating time resulted in the products with darker color, higher solubility, reducing sugar content, total dietary fiber and proportion of high molecular weight fiber fraction. An endothermic peak at 45-70 °C, having enthalpy of 1.66-2.14 J/g, was found from the samples processed under mild conditions (0.04-0.08% HCl, 100 °C, 60 min). However, harsher dextrinization conditions eliminated this endotherm. Dextrinization led to 1000-fold decrease in weight-average molecular weight (Mw) of the products, comparing to the native starch. Stronger processing conditions yielded the resistant dextrins with slightly higher Mw but composing of shorter branched chains. During dextrinization, hydrolysis was a predominant step, while transglucosidation and repolymerization played key roles in modifying molecular structure and properties, especially dietary fiber content, of resistant dextrins.

Different gelatinization characteristics of small and large barley starch granules impact their enzymatic hydrolysis and sugar production during mashing.

This study investigates the impact of different gelatinization characteristics of small and large barley starch granules on their enzymatic hydrolysis and sugar production during mashing. Therefore, a barley malt suspension was consecutively incubated at 45, 62, 72 and 78 °C to monitor starch behavior and enzymatic starch hydrolysis and sugar production. The combination of microscopic and rapid visco analyses showed that small starch granules persisted longer in the system and were present non-gelatinized at temperatures higher than 62 °C. HPAEC-PAD analysis showed that 8% of the total amount of starch, predominantly small granules, gelatinized at temperatures between 62 °C and 78 °C. Due to their delayed gelatinization in this system, their enzymatic hydrolysis yielded relatively more dextrins compared to what was observed for large granules. It was concluded that small granules should be taken into account when optimizing enzymatic hydrolysis of barley starch, like in brewing, distilling or bio-ethanol production.

Polymer Masked-Unmasked Protein Therapy: Identification of the Active Species after Amylase Activation of Dextrin-Colistin Conjugates.

Polymer masked-unmasked protein therapy (PUMPT) uses conjugation of a biodegradable polymer, such as dextrin, hyaluronic acid, or poly(l-glutamic acid), to mask a protein or peptide's activity; subsequent locally triggered degradation of the polymer at the target site regenerates bioactivity in a controllable fashion. Although the concept of PUMPT is well established, the relationship between protein unmasking and reinstatement of bioactivity is unclear. Here, we used dextrin-colistin conjugates to study the relationship between the molecular structure (degree of unmasking) and biological activity. Size exclusion chromatography was employed to collect fractions of differentially degraded conjugates and ultraperformance liquid chromatography-mass spectrometry (UPLC-MS) employed to characterize the corresponding structures. Antimicrobial activity was studied using a minimum inhibitory concentration (MIC) assay and confocal laser scanning microscopy of LIVE/DEAD-stained biofilms with COMSTAT analysis. In vitro toxicity of the degraded conjugate was assessed using an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. UPLC-MS revealed that the fully "unmasked" dextrin-colistin conjugate composed of colistin bound to at least one linker, whereas larger species were composed of colistin with varying lengths of glucose units attached. Increasing the degree of dextrin modification by succinoylation typically led to a greater number of linkers bound to colistin. Greater antimicrobial and antibiofilm activity were observed for the fully "unmasked" conjugate compared to the partially degraded species (MIC = 0.25 and 2-8 µg/mL, respectively), whereas dextrin conjugation reduced colistin's in vitro toxicity toward kidney cells, even after complete unmasking. This study highlights the importance of defining the structure-antimicrobial activity relationship for novel antibiotic derivatives and demonstrates the suitability of LC-MS to aid the design of biodegradable polymer-antibiotic conjugates.

Characterization of the Transglycosylation Reaction of 4-α-Glucanotransferase (MalQ) and Its Role in Glycogen Breakdown in Escherichia coli.

We first confirmed the involvement of MalQ (4-α-glucanotransferase) in Escherichia coli glycogen breakdown by both in vitro and in vivo assays. In vivo tests of the knock-out mutant, ΔmalQ, showed that glycogen slowly decreased after the stationary phase compared to the wild-type strain, indicating the involvement of MalQ in glycogen degradation. In vitro assays incubated glycogen-mimic substrate, branched cyclodextrin (maltotetraosyl-ß-CD: G4- ß-CD) and glycogen phosphorylase (GlgP)-limit dextrin with a set of variable combinations of E. coli enzymes, including GlgX (debranching enzyme), MalP (maltodextrin phosphorylase), GlgP and MalQ. In the absence of GlgP, the reaction of MalP, GlgX and MalQ on substrates produced glucose-1-P (glc-1-P) 3-fold faster than without MalQ. The results revealed that MalQ led to disproportionate G4 released from GlgP-limit dextrin to another acceptor, G4, which is phosphorylated by MalP. In contrast, in the absence of MalP, the reaction of GlgX, GlgP and MalQ resulted in a 1.6-fold increased production of glc-1-P than without MalQ. The result indicated that the G4-branch chains of GlgP-limit dextrin are released by GlgX hydrolysis, and then MalQ transfers the resultant G4 either to another branch chain or another G4 that can immediately be phosphorylated into glc-1-P by GlgP. Thus, we propose a model of two possible MalQ-involved pathways in glycogen degradation. The operon structure of MalP-defecting enterobacteria strongly supports the involvement of MalQ and GlgP as alternative pathways in glycogen degradation.

Enhanced depolymerization and utilization of raw lignocellulosic material by co-cultures of Ruminiclostridium thermocellum with hemicellulose-utilizing partners.

Ruminiclostridium thermocellum is one of the most promising candidates for consolidated bioprocessing (CBP) of low-cost lignocellulosic materials to biofuels but it still shows poor performance in its ability to deconstruct untreated lignocellulosic substrates. One promising approach to increase R. thermocellum's rate of hydrolysis is to co-culture this cellulose-specialist with partners that possess synergistic hydrolysis enzymes and metabolic capabilities. We have created co-cultures of R. thermocellum with two hemicellulose utilizers, Ruminiclostridium stercorarium and Thermoanaerobacter thermohydrosulfuricus, both of which secrete xylanolytic enzymes and utilize the pentose oligo- and monosaccharides that inhibit R. thermocellum's hydrolysis and metabolism. When grown on milled wheat straw, the co-cultures were able to solubilize up to 58% more of the total polysaccharides than the R. thermocellum mono-culture control. Repeated passaging of the co-cultures on wheat straw yielded stable populations with reduced R. thermocellum cell numbers, indicating competition for cellodextrins released from cellulose hydrolysis, although these stabilized co-cultures were still able to outperform the mono-culture controls. Repeated passaging on Avicel cellulose also yielded stable populations. Overall, the observed synergism suggests that co-culturing R. thermocellum with other members is a viable option for increasing the rate and extent of untreated lignocellulose deconstruction by R. thermocellum for CBP purposes.

Controlled release of dextrin-conjugated growth factors to support growth and differentiation of neural stem cells.

An essential aspect of stem cell in vitro culture and in vivo therapy is achieving sustained levels of growth factors to support stem cell survival and expansion, while maintaining their multipotency and differentiation potential. This study investigated the ability of dextrin (~74,000 g/mol; 27.8 mol% succinoylation) conjugated to epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF; or FGF-2) (3.9 and 6.7% w/w protein loading, respectively) to support the expansion and differentiation of stem cells in vitro via sustained, controllable growth factor release. Supplementation of mouse neural stem cells (mNSCs) with dextrin-growth factor conjugates led to greater and prolonged proliferation compared to unbound EGF/bFGF controls, with no detectable apoptosis after 7 days of treatment. Immunocytochemical detection of neural precursor (nestin) and differentiation (Olig2, MAP2, GFAP) markers verified that controlled release of dextrin-conjugated growth factors preserves stem cell properties of mNSCs for up to 7 days. These results show the potential of dextrin-growth factor conjugates for localized delivery of bioactive therapeutic agents to support stem cell expansion and differentiation, and as an adjunct to direct neuronal repair.

Evidence of Dextrin Hydrolyzing Enzymes in Cascade Hops ( Humulus lupulus).

Dry-hopping, the addition of hops to beer during or after fermentation, is a common practice in brewing to impart hoppy flavor to beer. Previously assumed to be inert ingredients, recent evidence suggests that hops contain biologically active compounds that may also extract into beer and complicate the brewing process by altering the final composition of beer. Experiments described herein provide evidence of microbial and/or plant-derived enzymes associated with hops ( Humulus lupulus) which can impact beer quality by influencing the composition of fermentable and nonfermentable carbohydrates in dry-hopped beer. Fully attenuated and packaged commercial lager beer was dry-hopped at a rate of 10 g hops/L beer with pelletized Cascade hops, dosed with 106 cells/mL of ale yeast, and incubated at 20 °C. Real extract of the treated beer declined significantly within several days with a reduction of 1 °P (% w/w) after 5 days and then slowly to a total reduction of approximately 2 °P after 40 days. When fully fermented, this was equivalent to the production of an additional 4.75% (v/v) of CO2 and an additional 1.3% (v/v) of alcohol. The refermentation of beer driven by dry-hopping was attributed to the low but persistent activities of several starch degrading enzymes present in Cascade hops including amyloglucosidase, α-amylase, ß-amylase, and limit dextrinase. The effect of hop-derived enzymes on beer was time, temperature, and dose-dependent. Characterizing bioactive enzymes in hops will help hop suppliers and brewers to address the unexpected quality and safety issues surrounding hopping practices in beer.

A new interpretation of sulfate activation of rabbit muscle glycogen phosphorylase.

It is widely known that sulfate ion at high concentration serves like an allosteric activator of glycogen phosphorylase (GP). Based on the crystallographic studies on GP, it has been assumed that the sulfate ion is bound close to the phosphorylatable Ser14 site of nonactivated GP, causing a conformational change to catalytically-active GP. However, there are also reports that sulfate ion inhibits allosterically-activated GP by preventing the phosphate substrate from attaching to the catalytic site. In the present study, using a high concentration of sulfate ion, significant enhancement of GP activity was observed when macromolecular glycogen was used as substrate but not when smaller maltohexaose was used. In glycogen solution, nonreducing-end glucose residues are localized on the surface of glycogen and are not distributed homogenously in the solution. Using cyclodextrin-immobilized column chromatography, we found that sulfate at high concentration promoted GP-dextrin binding through the dextrin-binding site (DBS) located away from the catalytic site. This result is consistent with the properties of the DBSs found in glycogen-debranching enzyme and ß-amylase. Therefore, we propose a new interpretation of the sulfate activation of GP, wherein sulfate ions at high concentration promote glycogen-binding to the DBS directly, and glycogen-binding to the catalytic site indirectly. Our findings were successfully applied to the affinity purification of porcine brain GP.

Enhanced cellobiose fermentation by engineered Saccharomyces cerevisiae expressing a mutant cellodextrin facilitator and cellobiose phosphorylase.

To efficiently ferment intermediate cellodextrins released during cellulose hydrolysis, Saccharomyces cerevisiae has been engineered by introduction of a heterologous cellodextrin utilizing pathway consisting of a cellodextrin transporter and either an intracellular ß-glucosidase or a cellobiose phosphorylase. Among two types of cellodextrin transporters, the passive facilitator CDT-2 has not enabled better cellobiose fermentation than the active transporter CDT-1, which suggests that the CDT-2 might be engineered to provide energetic benefits over the active transporter in cellobiose fermentation. We attempted to improve cellobiose transporting activity of CDT-2 through laboratory evolution. Nine rounds of a serial subculture of S. cerevisiae expressing CDT-2 and cellobiose phosphorylase on cellobiose led to the isolation of an evolved strain capable of fermenting cellobiose to ethanol 10-fold faster than the original strain. After sequence analysis of the isolated CDT-2, a single point mutation on CDT-2 (N306I) was revealed to be responsible for enhanced cellobiose fermentation. Also, the engineered strain expressing the mutant CDT-2 with cellobiose phosphorylase showed a higher ethanol yield than the engineered strain expressing CDT-1 and intracellular ß-glucosidase under anaerobic conditions, suggesting that CDT-2 coupled with cellobiose phosphorylase may be better choices for efficient production of cellulosic ethanol with the engineered yeast.