Similarities and differences in the biochemical and enzymological properties of the four isomaltases from Saccharomyces cerevisiae

cAMP in budding yeast: Also a messenger for sucrose metabolism?

S. cerevisiae (or budding yeast) is an important micro-organism for sucrose-based fermentation in biotechnology. Yet, it is largely unknown how budding yeast adapts to sucrose transitions. Sucrose can only be metabolized when the invertase or the maltose machinery are expressed and we propose that the Gpr1p receptor signals extracellular sucrose availability via the cAMP peak to adapt cells accordingly. A transition to sucrose or glucose gave a transient cAMP peak which was maximally induced for sucrose. When transitioned to sucrose, cAMP signalling mutants showed an impaired cAMP peak together with a lower growth rate, a longer lag phase and a higher final OD600 compared to a glucose transition. These effects were not caused by altered activity or expression of enzymes involved in sucrose metabolism and imply a more general metabolic adaptation defect. Basal cAMP levels were comparable among the mutant strains, suggesting that the transient cAMP peak is required to adapt cells correctly to sucrose. We propose that the short-term dynamics of the cAMP signalling cascade detects long-term extracellular sucrose availability and speculate that its function is to maintain a fermentative phenotype at continuously low glucose and fructose concentrations.

Crucial aspects of metabolism and cell biology relating to industrial production and processing of Saccharomyces biomass

The multitude of applications to which Saccharomyces spp. are put makes these yeasts the most prolific of industrial microorganisms. This review considers biological aspects pertaining to the manufacture of industrial yeast biomass. It is proposed that the production of yeast biomass can be considered in two distinct but interdependent phases. Firstly, there is a cell replication phase that involves reproduction of cells by their transitions through multiple budding and metabolic cycles. Secondly, there needs to be a cell conditioning phase that enables the accrued biomass to withstand the physicochemical challenges associated with downstream processing and storage. The production of yeast biomass is not simply a case of providing sugar, nutrients, and other growth conditions to enable multiple budding cycles to occur. In the latter stages of culturing, it is important that all cells are induced to complete their current budding cycle and subsequently enter into a quiescent state engendering robustness. Both the cell replication and conditioning phases need to be optimized and considered in concert to ensure good biomass production economics, and optimum performance of industrial yeasts in food and fermentation applications. Key features of metabolism and cell biology affecting replication and conditioning of industrial Saccharomyces are presented. Alternatives for growth substrates are discussed, along with the challenges and prospects associated with defining the genetic bases of industrially important phenotypes, and the generation of new yeast strains."I must be cruel only to be kind: Thus bad begins, and worse remains behind." William Shakespeare: Hamlet, Act 3, Scene 4.

Modeling and evaluation of the sucrose-degrading activity of recombinantly produced oligo-1,6-glucosidase from A. gonensis

Fructose is the most preferred sugar to provide benefits for sweetening and health. As many industrial enzymes are used to produce High Fructose Syrup (HFS), it is vital to explore alternative enzymes for fructose production. Oligo-α-1,6-glucosidase (O-1-6-glucosidase) hydrolyzes non-reducing ends of isomaltooligosaccharides, panose, palatinose, and an a-limit dextrin by breaking α-1,6-glucoside bonds, although it generally has no activity on α-1,4-glucoside bonds of maltooligosaccharides. In this study, sucrose-hydrolyzing activity of O-1-6-glucosidase of thermophilic A. gonensis was evaluated. For this purpose, O-1-6-glucosidase gene region of A. gonensis was cloned in the pET28(a)+ expression vector, the expression product was purified, modeled, and biochemically characterized. The optimal activity of the enzyme was to be at pH 7.0 and 60 °C. The enzyme activity was halved at the end of the 276th h at 60 °C. The enzyme maintained its activity even after 300 h at pH 6.0-10.0. The values of Km, Vmax, kcat, and kcat/Km were determined as 44.69 ± 1.27 mM, 6.28 ± 0.05 µmoL/min/mg protein, 6.70 1/s and 0.15 1/mMs-1, respectively. While Zn2+, Cu2+, Pb2+, Ag2+, Fe3+, Hg2+, and Al2+ metal ions inhibited O-1-6-glucosidase, Mn2+, Fe2+, and Mg2+ ions activated the enzyme. Consequently, A. gonensis O-1-6-glucosidase (rAgoSuc2) has interesting properties, especially for HFS production.

Alpha-Glucosidase Inhibitory Assay-Screened Isolation and Molecular Docking Model from Bauhinia pulla Active Compounds

The aim of this research was to establish the constituents of Bauhinia pulla as anti-diabetic agents. A phytochemistry analysis was conducted by chromatographic and spectroscopic techniques. The alpha-glucosidase inhibitory assay screening resulted in the isolation of eight known compounds of quercetin, quercitrin, luteolin, 5-deoxyluteolin, 4-methyl ether isoliquiritigenin, 3,2',4'-trihydroxy-4-methoxychalcone, stigmasterol and β-sitosterol. Ethanol leaf extracts showed potential effects, which led to a strong inhibitory activity of isolated quercetin at 138.95 µg/mL and 5.41 µg/mL of IC₅₀, respectively. The docking confirmed that flavonoids and chalcones had the same potential binding sites and responsibilities for their activity. This study was the first report of Bauhinia pulla chemical constituents and its alpha-glucosidase inhibition.

Improving the Utilization of Isomaltose and Panose by Lager Yeast Saccharomyces pastorianus

Approximately 25% of all carbohydrates in industrial worts are poorly, if at all, fermented by brewing yeast. This includes dextrins, β-glucans, arabinose, xylose, disaccharides such as isomaltose, nigerose, kojibiose, and trisaccharides such as panose and isopanose. As the efficient utilization of carbohydrates during the wort’s fermentation impacts the alcohol yield and the organoleptic traits of the product, developing brewing strains with enhanced abilities to ferment subsets of these sugars is highly desirable. In this study, we developed Saccharomyces pastorianus laboratory yeast strains with a superior capacity to grow on isomaltose and panose. First, we designed a plasmid toolbox for the stable integration of genes into lager strains. Next, we used the toolbox to elevate the levels of the α-glucoside transporter Agt1 and the major isomaltase Ima1. This was achieved by integrating synthetic AGT1 and IMA1 genes under the control of strong constitutive promoters into defined genomic sites. As a result, strains carrying both genes showed a superior capacity to grow on panose and isomaltose, indicating that Ima1 and Agt1 act in synergy to consume these sugars. Our study suggests that non-GMO strategies aiming to develop strains with improved isomaltose and panose utilization could include identifying strains that overexpress AGT1 and IMA1.

Molecular characterization and heterologous expression of two α-glucosidases from Metschnikowia spp, both producers of honey sugars

BACKGROUND

α-Glucosidases are widely distributed enzymes with a varied substrate specificity that are traditionally used in biotechnological industries based on oligo- and polysaccharides as starting materials. According to amino acid sequence homology, α-glucosidases are included into two major families, GH13 and GH31. The members of family GH13 contain several α-glucosidases with confirmed hydrolytic activity on sucrose. Previously, a sucrose splitting activity from the nectar colonizing yeast Metschnikowia reukaufii which produced rare sugars with α-(1→1), α-(1→3) and α-(1→6) glycosidic linkages from sucrose was described.

RESULTS

In this study, genes codifying for α-glucosidases from the nectaries yeast M. gruessii and M. reukaufii were characterised and heterologously expressed in Escherichia coli for the first time. Recombinant proteins (Mg-αGlu and Mr-αGlu) were purified and biochemically analysed. Both enzymes mainly displayed hydrolytic activity towards sucrose, maltose and p-nitrophenyl-α-D-glucopyranoside. Structural analysis of these proteins allowed the identification of common features from the α-amylase family, in particular from glycoside hydrolases that belong to family GH13. The three acidic residues comprising the catalytic triad were identified and their relevance for the protein hydrolytic mechanism confirmed by site-directed mutagenesis. Recombinant enzymes produced oligosaccharides naturally present in honey employing sucrose as initial substrate and gave rise to mixtures with the same products profile (isomelezitose, trehalulose, erlose, melezitose, theanderose and esculose) previously obtained with M. reukaufii cell extracts. Furthermore, the same enzymatic activity was detected with its orthologous Mg-αGlu from M. gruessii. Interestingly, the isomelezitose amounts obtained in reactions mediated by the recombinant proteins, ~ 170 g/L, were the highest reported so far.

CONCLUSIONS

Mg/Mr-αGlu were heterologously overproduced and their biochemical and structural characteristics analysed. The recombinant α-glucosidases displayed excellent properties in terms of mild reaction conditions, in addition to pH and thermal stability. Besides, the enzymes produced a rare mixture of hetero-gluco-oligosaccharides by transglucosylation, mainly isomelezitose and trehalulose. These compounds are natural constituents of honey which purification from this natural source is quite unviable, what make these enzymes very interesting for the biotechnological industry. Finally, it should be remarked that these sugars have potential applications as food additives due to their suitable sweetness, viscosity and humectant capacity.

Assessing Population Diversity of Brettanomyces Yeast Species and Identification of Strains for Brewing Applications

Brettanomyces yeasts have gained popularity in many sectors of the biotechnological industry, specifically in the field of beer production, but also in wine and ethanol production. Their unique properties enable Brettanomyces to outcompete conventional brewer’s yeast in industrially relevant traits such as production of ethanol and pleasant flavors. Recent advances in next-generation sequencing (NGS) and high-throughput screening techniques have facilitated large population studies allowing the selection of appropriate yeast strains with improved traits. In order to get a better understanding of Brettanomyces species and its potential for beer production, we sequenced the whole genome of 84 strains, which we make available to the scientific community and carried out several in vitro assays for brewing-relevant properties. The collection includes isolates from different substrates and geographical origin. Additionally, we have included two of the oldest Carlsberg Research Laboratory isolates. In this study, we reveal the phylogenetic pattern of Brettanomyces species by comparing the predicted proteomes of each strain. Furthermore, we show that the Brettanomyces collection is well described using similarity in genomic organization, and that there is a direct correlation between genomic background and phenotypic characteristics. Particularly, genomic patterns affecting flavor production, maltose assimilation, beta-glucosidase activity, and phenolic off-flavor (POF) production are reported. This knowledge yields new insights into Brettanomyces population survival strategies, artificial selection pressure, and loss of carbon assimilation traits. On a species-specific level, we have identified for the first time a POF negative Brettanomyces anomalus strain, without the main spoilage character of Brettanomyces species. This strain (CRL-90) has lost DaPAD1, making it incapable of converting ferulic acid to 4-ethylguaiacol (4-EG) and 4-ethylphenol (4-EP). This loss of function makes CRL-90 a good candidate for the production of characteristic Brettanomyces flavors in beverages, without the contaminant increase in POF. Overall, this study displays the potential of exploring Brettanomyces yeast species biodiversity to find strains with relevant properties applicable to the brewing industry.

Characterization of a Maltase from an Early-Diverged Non-Conventional Yeast Blastobotrys adeninivorans

Genome of an early-diverged yeast Blastobotrys (Arxula) adeninivorans (Ba) encodes 88 glycoside hydrolases (GHs) including two α-glucosidases of GH13 family. One of those, the rna_ARAD1D20130g-encoded protein (BaAG2; 581 aa) was overexpressed in Escherichia coli, purified and characterized. We showed that maltose, other maltose-like substrates (maltulose, turanose, maltotriose, melezitose, malto-oligosaccharides of DP 4‒7) and sucrose were hydrolyzed by BaAG2, whereas isomaltose and isomaltose-like substrates (palatinose, α-methylglucoside) were not, confirming that BaAG2 is a maltase. BaAG2 was competitively inhibited by a diabetes drug acarbose (Ki = 0.8 µM) and Tris (Ki = 70.5 µM). BaAG2 was competitively inhibited also by isomaltose-like sugars and a hydrolysis product-glucose. At high maltose concentrations, BaAG2 exhibited transglycosylating ability producing potentially prebiotic di- and trisaccharides. Atypically for yeast maltases, a low but clearly recordable exo-hydrolytic activity on amylose, amylopectin and glycogen was detected. Saccharomyces cerevisiae maltase MAL62, studied for comparison, had only minimal ability to hydrolyze these polymers, and its transglycosylating activity was about three times lower compared to BaAG2. Sequence identity of BaAG2 with other maltases was only moderate being the highest (51%) with the maltase MalT of Aspergillus oryzae.

Integrated Robotic Mini Bioreactor Platform for Automated, Parallel Microbial Cultivation With Online Data Handling and Process Control

During process development, the experimental search space is defined by the number of experiments that can be performed in specific time frames but also by its sophistication (e.g., inputs, sensors, sampling frequency, analytics). High-throughput liquid-handling stations can perform a large number of automated experiments in parallel. Nevertheless, the experimental data sets that are obtained are not always relevant for development of industrial bioprocesses, leading to a high rate of failure during scale-up. We present an automated mini bioreactor platform that enables parallel cultivations in the milliliter scale with online monitoring and control, well-controlled conditions, and advanced feeding strategies similar to industrial processes. The combination of two liquid handlers allows both automated mini bioreactor operation and at-line analysis in parallel. A central database enables end-to-end data exchange and fully integrated device and process control. A model-based operation algorithm allows for the accurate performance of complex cultivations for scale-down studies and strain characterization via optimal experimental redesign, significantly increasing the reliability and transferability of data throughout process development. The platform meets the tradeoff between experimental throughput and process control and monitoring comparable to laboratory-scale bioreactors.

Extracellular maltotriose hydrolysis by Saccharomyces cerevisiae cells lacking the AGT1 permease

In brewing, maltotriose is the least preferred sugar for uptake by Saccharomyces cerevisiae cells. Although the AGT1 permease is required for efficient maltotriose fermentation, we have described a new phenotype in some agt1Δ strains of which the cells do not grow on maltotriose during the first 3-4 days of incubation, but after that, they start to grow on the sugar aerobically. Aiming to characterize this new phenotype, we performed microarray gene expression analysis which indicated upregulation of high-affinity glucose transporters (HXT4, HXT6 and HXT7) and α-glucosidases (MAL12 and IMA5) during this delayed cellular growth. Since these results suggested that this phenotype might be due to extracellular hydrolysis of maltotriose, we attempted to detect glucose in the media during growth. When an hxt-null agt1Δ strain was grown on maltotriose, it also showed the delayed growth on this carbon source, and glucose accumulated in the medium during maltotriose consumption. Considering that the poorly characterized α-glucosidase encoded by IMA5 was among the overexpressed genes, we deleted this gene from an agt1Δ strain that showed delayed growth on maltotriose. The ima5Δ agt1Δ strain showed no maltotriose utilization even after 200 h of incubation, suggesting that IMA5 is likely responsible for the extracellular maltotriose hydrolysis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Maltotriose is the second most abundant sugar present in brewing. However, many yeast strains have difficulties to consume maltotriose, mainly because of its low uptake rate by the yeast cells when compared to glucose and maltose uptake. The AGT1 permease is required for efficient maltotriose fermentation, but some strains deleted in this gene are still able to grow on maltotriose after an extensive lag phase. This manuscript shows that such delayed growth on maltotriose is a consequence of extracellular hydrolysis of the sugar. Our results also indicate that the IMA5-encoded α-glucosidase is likely the enzyme responsible for this phenotype.

Genome Mining of Non-Conventional Yeasts: Search and Analysis of MAL Clusters and Proteins

Genomic clustering of functionally related genes is rare in yeasts and other eukaryotes with only few examples available. Here, we summarize our data on a nontelomeric MAL cluster of a non-conventional methylotrophic yeast Ogataea (Hansenula) polymorpha containing genes for α-glucosidase MAL1, α-glucoside permease MAL2 and two hypothetical transcriptional activators. Using genome mining, we detected MAL clusters of varied number, position and composition in many other maltose-assimilating non-conventional yeasts from different phylogenetic groups. The highest number of MAL clusters was detected in Lipomyces starkeyi while no MAL clusters were found in Schizosaccharomyces pombe and Blastobotrys adeninivorans. Phylograms of α-glucosidases and α-glucoside transporters of yeasts agreed with phylogenesis of the respective yeast species. Substrate specificity of unstudied α-glucosidases was predicted from protein sequence analysis. Specific activities of Scheffersomycesstipitis α-glucosidases MAL7, MAL8, and MAL9 heterologously expressed in Escherichia coli confirmed the correctness of the prediction-these proteins were verified promiscuous maltase-isomaltases. α-Glucosidases of earlier diverged yeasts L. starkeyi, B. adeninivorans and S. pombe showed sequence relatedness with α-glucosidases of filamentous fungi and bacilli.

Evidence for loss and reacquisition of alcoholic fermentation in a fructophilic yeast lineage

Fructophily is a rare trait that consists of the preference for fructose over other carbon sources. Here, we show that in a yeast lineage (the Wickerhamiella/Starmerella, W/S clade) comprised of fructophilic species thriving in the high-sugar floral niche, the acquisition of fructophily is concurrent with a wider remodeling of central carbon metabolism. Coupling comparative genomics with biochemical and genetic approaches, we gathered ample evidence for the loss of alcoholic fermentation in an ancestor of the W/S clade and subsequent reinstatement through either horizontal acquisition of homologous bacterial genes or modification of a pre-existing yeast gene. An enzyme required for sucrose assimilation was also acquired from bacteria, suggesting that the genetic novelties identified in the W/S clade may be related to adaptation to the high-sugar environment. This work shows how even central carbon metabolism can be remodeled by a surge of HGT events.

Cells build their components, such as the molecular machinery that helps them obtain energy from their environment, by following the instructions contained in genes. This genetic information is usually transferred from parents to offspring. Over the course of several generations, genes can accumulate small changes and the molecules they code for can acquire new roles: yet, this process is normally slow. However, certain organisms can also obtain completely new genes by ‘stealing’ them from other species. For example, yeasts, such as the ones used to make bread and beer, can take genes from nearby bacteria. This ‘horizontal gene transfer’ helps organisms to rapidly gain new characteristics, which is particularly useful if the environment changes quickly.

One way that yeasts get the energy they need is by breaking down sugars through a process called alcoholic fermentation. To do this, most yeast species prefer to use a sugar called glucose, but a small group of ‘fructophilic’ species instead favors a type of sugar known as fructose. Scientists do not know exactly how fructophilic yeasts came to be, but there is some evidence horizontal gene transfers may have been involved in the process.

Now, Gonçalves et al. have compared the genetic material of fructophilic yeasts with that of other groups of yeasts . Comparing genetic material helps scientists identify similarities and differences between species, and gives clues about why specific genetic features first evolved.

The experiments show that, early in their history, fructophilic yeasts lost the genes that allowed them to do alcoholic fermentation, probably since they could obtain energy in a different way. However, at a later point in time, these yeasts had to adapt to survive in flower nectar, an environment rich in sugar. They then favored fructose as their source of energy, possibly because this sugar can compensate more effectively for the absence of alcoholic fermentation. Later, the yeasts acquired a gene from nearby bacteria, which allowed them to do alcoholic fermentation again: this improved their ability to use the other sugars present in flower nectars.

When obtaining energy, yeasts and other organisms produce substances that are relevant to industry. Studying natural processes of evolution can help scientists understand how organisms can change the way they get their energy and adapt to new challenges. In turn, this helps to engineer yeasts into ‘cell factories’ that produce valuable chemicals in environmentally friendly and cost-effective ways.

Rhamnolipids production from sucrose by engineered Saccharomyces cerevisiae

Biosurfactants are biological tensioactive agents that can be used in the cosmetic and food industries. Rhamnolipids are glycolipid biosurfactants naturally produced by Pseudomonas aeruginosa and are composed of one or two rhamnose molecules linked to beta-hydroxy fatty acid chains. These compounds are green alternatives to petrochemical surfactants, but their large-scale production is still in its infancy, hindered due to pathogenicity of natural producer, high substrate and purification costs and low yields and productivities. This study, for the first time, aimed at producing mono-rhamnolipids from sucrose by recombinant GRAS Saccharomyces cerevisiae strains. Six enzymes from P. aeruginosa involved in mono-rhamnolipid biosynthesis were functionally expressed in the yeast. Furthermore, its SUC2 invertase gene was disrupted and a sucrose phosphorylase gene from Pelomonas saccharophila was also expressed to reduce the pathway's overall energy requirement. Two strains were constructed aiming to produce mono-rhamnolipids and the pathway's intermediate dTDP-L-rhamnose. Production of both molecules was analyzed by confocal microscopy and mass spectrometry, respectively. These strains displayed, for the first time as a proof of concept, the potential of production of these molecules by a GRAS eukaryotic microorganism from an inexpensive substrate. These constructs show the potential to further improve rhamnolipids production in a yeast-based industrial bioprocess.

Receptor protein of Lysinibacillus sphaericus mosquito-larvicidal toxin displays amylomaltase activity

The activated binary toxin (BinAB) from Lysinibacillus sphaericus binds to surface receptor protein (Cqm1) on the midgut cell membrane and kills Culex quinquefasciatus larvae on internalization. Cqm1 is attached to cells via a glycosyl-phosphatidylinositol (GPI) anchor. It has been classified as a member of glycoside hydrolase family 13 of the CAZy database. Here, we report characterization of the ordered domain (residues 23-560) of Cqm1. Gene expressing Cqm1 of BinAB susceptible mosquito was chemically synthesized and the protein was purified using E. coli expression system. Values for the Michaelis-Menten kinetics parameters towards 4-nitrophenyl α-D-glucopyranoside (α-pNPG) substrate were estimated to be 0.44 mM (Km) and 1.9 s^-1 (kcat). Thin layer chromatography experiments established Cqm1 as α-glucosidase competent to cleave α-1,4-glycosidic bonds of maltose and maltotriose with high glycosyltransferase activity to form glucose-oligomers. The observed hydrolysis and synthesis of glucose-oligomers is consistent with open and accessible active-site in the structural model. The protein also hydrolyses glycogen and sucrose. These activities suggest that Cqm1 may be involved in carbohydrate metabolism in mosquitoes. Further, toxic BinA component does not inhibit α-glucosidase activity of Cqm1, while BinB reduced the activity by nearly 50%. The surface plasmon resonance study reveals strong binding of BinB with Cqm1 (Kd, 9.8 nM). BinA interaction with Cqm1 however, is 1000-fold weaker. Notably the estimated Kd values match well with dissociation constants reported earlier with larvae brush border membrane fractions. The Cqm1 protein forms a stable dimer that is consistent with its apical localization in lipid rafts. Its melting temperature (T_m) as observed by thermofluor-shift assay is 51.5 °C and Ca²⁺ provides structural stability to the protein.

Elimination of sucrose transport and hydrolysis in Saccharomyces cerevisiae: a platform strain for engineering sucrose metabolism

Many relevant options to improve efficacy and kinetics of sucrose metabolism in Saccharomyces cerevisiae and, thereby, the economics of sucrose-based processes remain to be investigated. An essential first step is to identify all native sucrose-hydrolysing enzymes and sucrose transporters in this yeast, including those that can be activated by suppressor mutations in sucrose-negative strains. A strain in which all known sucrose-transporter genes (MAL11, MAL21, MAL31, MPH2, MPH3) were deleted did not grow on sucrose after 2 months of incubation. In contrast, a strain with deletions in genes encoding sucrose-hydrolysing enzymes (SUC2, MAL12, MAL22, MAL32) still grew on sucrose. Its specific growth rate increased from 0.08 to 0.25 h⁻¹ after sequential batch cultivation. This increase was accompanied by a 3-fold increase of in vitro sucrose-hydrolysis and isomaltase activities, as well as by a 3- to 5-fold upregulation of the isomaltase-encoding genes IMA1 and IMA5. One-step Cas9-mediated deletion of all isomaltase-encoding genes (IMA1-5) completely abolished sucrose hydrolysis. Even after 2 months of incubation, the resulting strain did not grow on sucrose. This sucrose-negative strain can be used as a platform to test metabolic engineering strategies and for fundamental studies into sucrose hydrolysis or transport.

Comparative analysis of the expression level of recombinant ginsenoside-transforming β-glucosidase in GRAS hosts and mass production of the ginsenoside Rh2-Mix

The ginsenoside Rh₂, a pharmaceutically active component of ginseng, is known to have anticancer and antitumor effects. However, white ginseng and red ginseng have extremely low concentrations of Rh₂ or Rh₂-Mix [20(S)-Rh₂, 20(R)-Rh₂, Rk₂, and Rh₃]. To enhance the production of food-grade ginsenoside Rh₂, an edible enzymatic bioconversion technique was developed adopting GRAS host strains. A β-glucosidase (BglPm), which has ginsenoside conversion ability, was expressed in three GRAS host strains (Corynebacterium glutamicum, Saccharomyces cerevisiae and Lactococus lactis) by using a different vector system. Enzyme activity in these three GRAS hosts were 75.4%, 11.5%, and 9.3%, respectively, compared to that in the E. coli pGEX 4T-1 expression system. The highly expressed BglPm_C in C. glutamicum can effectively transform the ginsenoside Rg₃-Mix [20(S)-Rg₃, 20(R)-Rg₃, Rk₁, Rg₅] to Rh₂-Mix [20(S)-Rh₂, 20(R)-Rh₂, Rk₂, Rh₃] using a scaled-up biotransformation reaction, which was performed in a 10-L jar fermenter at pH 6.5/7.0 and 37°C for 24 h. To our knowledge, this is the first report in which 50 g of PPD-Mix (Rb₁, Rb₂, Rb₃, R_c, and Rd) as a starting substrate was converted to ginsenoside Rg₃-Mix by acid heat treatment and then 24.5-g Rh₂-Mix was obtained by enzymatic transformation of Rg₃-Mix through by BglPm_C. Utilization of this enzymatic method adopting a GRAS host could be usefully exploited in the preparation of ginsenoside Rh₂-Mix in cosmetics, functional food, and pharmaceutical industries, thereby replacing the E. coli expression system.

Maltase protein of Ogataea (Hansenula) polymorpha is a counterpart to the resurrected ancestor protein ancMALS of yeast maltases and isomaltases

Saccharomyces cerevisiae maltases use maltose, maltulose, turanose and maltotriose as substrates, isomaltases use isomaltose, α‐methylglucoside and palatinose and both use sucrose. These enzymes are hypothesized to have evolved from a promiscuous α‐glucosidase ancMALS through duplication and mutation of the genes. We studied substrate specificity of the maltase protein MAL1 from an earlier diverged yeast, Ogataea polymorpha (Op), in the light of this hypothesis. MAL1 has extended substrate specificity and its properties are strikingly similar to those of resurrected ancMALS. Moreover, amino acids considered to determine selective substrate binding are highly conserved between Op MAL1 and ancMALS. Op MAL1 represents an α‐glucosidase in which both maltase and isomaltase activities are well optimized in a single enzyme. Substitution of Thr200 (corresponds to Val216 in S. cerevisiae isomaltase IMA1) with Val in MAL1 drastically reduced the hydrolysis of maltose‐like substrates (α‐1,4‐glucosides), confirming the requirement of Thr at the respective position for this function. Differential scanning fluorimetry (DSF) of the catalytically inactive mutant Asp199Ala of MAL1 in the presence of its substrates and selected monosaccharides suggested that the substrate‐binding pocket of MAL1 has three subsites (–1, +1 and +2) and that binding is strongest at the –1 subsite. The DSF assay results were in good accordance with affinity (K_m) and inhibition (K_i) data of the enzyme for tested substrates, indicating the power of the method to predict substrate binding. Deletion of either the maltase (MAL1) or α‐glucoside permease (MAL2) gene in Op abolished the growth of yeast on MAL1 substrates, confirming the requirement of both proteins for usage of these sugars. © 2016 The Authors. Yeast published by John Wiley & Sons, Ltd.

Sucrose and Saccharomyces cerevisiae: a relationship most sweet

Sucrose is an abundant, readily available and inexpensive substrate for industrial biotechnology processes and its use is demonstrated with much success in the production of fuel ethanol in Brazil. Saccharomyces cerevisiae, which naturally evolved to efficiently consume sugars such as sucrose, is one of the most important cell factories due to its robustness, stress tolerance, genetic accessibility, simple nutrient requirements and long history as an industrial workhorse. This minireview is focused on sucrose metabolism in S. cerevisiae, a rather unexplored subject in the scientific literature. An analysis of sucrose availability in nature and yeast sugar metabolism was performed, in order to understand the molecular background that makes S. cerevisiae consume this sugar efficiently. A historical overview on the use of sucrose and S. cerevisiae by humans is also presented considering sugarcane and sugarbeet as the main sources of this carbohydrate. Physiological aspects of sucrose consumption are compared with those concerning other economically relevant sugars. Also, metabolic engineering efforts to alter sucrose catabolism are presented in a chronological manner. In spite of its extensive use in yeast-based industries, a lot of basic and applied research on sucrose metabolism is imperative, mainly in fields such as genetics, physiology and metabolic engineering.