Analysis of the raw starch-binding domain by mutation of a glucoamylase from Aspergillus awamori var. kawachi expressed in Saccharomyces cerevisiae

Co-production of sugars and aroma compounds from tobacco waste using biomass-degrading enzymes produced by Aspergillus brunneoviolaceus Ab-10

Biomass-degrading enzymes produced by microorganisms have a great potential in the processing of agricultural wastes. In order to produce suitable biomass-degrading enzymes for releasing sugars and aroma compounds from tobacco scraps, the feasibility of directly using the scraps as a carbon source for enzyme production was investigated in this study. By comparative studies of ten fungal strains isolated from tobacco leaves, Aspergillus brunneoviolaceus Ab-10 was found to produce an efficient enzyme mixture for the saccharification of tobacco scraps. Proteomic analysis identified a set of plant biomass-degrading enzymes in the enzyme mixture, including amylases, hemicellulases, cellulases and pectinases. At a substrate concentration of 100 g/L and enzyme dosage of 4 mg/g, glucose of 17.6 g/L was produced from tobacco scraps using the crude enzyme produced by A. brunneoviolaceus Ab-10. In addition, the contents of 23 volatile molecules, including the aroma compounds 4-ketoisophorone and benzyl alcohol, were significantly increased after the enzymatic treatment. The results provide a strategy for valorization of tobacco waste by integrating the production of biomass-degrading enzymes into the tobacco scrap processing system.

Mixed food waste valorization using a thermostable glucoamylase enzyme produced by a newly isolated filamentous fungus: A sustainable biorefinery approach

Food waste is a lucrative source of complex nutrients, which can be transformed into a multitude of bioproducts by the aid of microbial cell factories. The current study emphasizes isolating Glucoamylase enzyme (GA) producing strains that can effectively break down mixed food waste (MW), which serves as a substrate for biomanufacturing. The screening procedure relied heavily on the growth of isolated fungi on starch agar media, to specifically identify the microbes with the highest starch hydrolysis potential. A strain displayed the highest GA activity of 2.9 ± 0.14 U/ml which was selected and identified as Aspergillus fumigatus via molecular methods of identification. Exposure of the A. fumigatus with 200 mM Ethyl methanesulphonate (EMS) led to a 23.79% increase compared to the wild-type GA. The growth conditions like cultivation temperature or the number of spores in the inoculum were investigated. Further, maximum GA activity was exhibited at pH 5, 55 °C, and at 5 mM Ca2+ concentration. The GA showed thermostability, retaining activity even after long periods of exposure to temperatures as high as 95 °C. The improvement of hydrolysis of MW was achieved by Taguchi design where a maximum yield of 0.57 g g-1 glucose was obtained in the hydrolysate. This study puts forth the possibility that mixed food waste, despite containing spices and other microbial growth-inhibitory substances, can be efficiently hydrolyzed to release glucose units, by robust fungal cell factories. The glucose released can then be utilized as a carbon source for the production of value-added products.

Making Traditional Japanese Distilled Liquor, Shochu and Awamori, and the Contribution of White and Black Koji Fungi

The traditional Japanese single distilled liquor, which uses koji and yeast with designated ingredients, is called "honkaku shochu." It is made using local agricultural products and has several types, including barley shochu, sweet potato shochu, rice shochu, and buckwheat shochu. In the case of honkaku shochu, black koji fungus (Aspergillus luchuensis) or white koji fungus (Aspergillus luchuensis mut. kawachii) is used to (1) saccharify the starch contained in the ingredients, (2) produce citric acid to prevent microbial spoilage, and (3) give the liquor its unique flavor. In order to make delicious shochu, when cultivating koji fungus during the shochu production process, we use a unique temperature control method to ensure that these three important elements, which greatly affect the taste of the produced liquor, are balanced without any excess or deficiency. This review describes in detail the production method of honkaku shochu, a distilled spirit unique to Japan and whose market is expected to expand worldwide, with special attention paid to the koji fungi cultivation step. Furthermore, we describe the history of the koji fungi used today in the production of shochu, and we provide a thorough explanation of the characteristics of each koji fungi. We also report the latest research progress on this topic.

A Rubisco-binding protein is required for normal pyrenoid number and starch sheath morphology in Chlamydomonas reinhardtii

A phase-separated, liquid-like organelle called the pyrenoid mediates CO2 fixation in the chloroplasts of nearly all eukaryotic algae. While most algae have 1 pyrenoid per chloroplast, here we describe a mutant in the model alga Chlamydomonas that has on average 10 pyrenoids per chloroplast. Characterization of the mutant leads us to propose a model where multiple pyrenoids are favored by an increase in the surface area of the starch sheath that surrounds and binds to the liquid-like pyrenoid matrix. We find that the mutant's phenotypes are due to disruption of a gene, which we call StArch Granules Abnormal 1 (SAGA1) because starch sheath granules, or plates, in mutants lacking SAGA1 are more elongated and thinner than those of wild type. SAGA1 contains a starch binding motif, suggesting that it may directly regulate starch sheath morphology. SAGA1 localizes to multiple puncta and streaks in the pyrenoid and physically interacts with the small and large subunits of the carbon-fixing enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), a major component of the liquid-like pyrenoid matrix. Our findings suggest a biophysical mechanism by which starch sheath morphology affects pyrenoid number and CO2-concentrating mechanism function, advancing our understanding of the structure and function of this biogeochemically important organelle. More broadly, we propose that the number of phase-separated organelles can be regulated by imposing constraints on their surface area.

Enhanced Bioethanol Production from Potato Peel Waste Via Consolidated Bioprocessing with Statistically Optimized Medium

In this study, an extensive screening was undertaken to isolate some amylolytic microorganisms capable of producing bioethanol from starchy biomass through Consolidated Bioprocessing (CBP). A total of 28 amylolytic microorganisms were isolated, from which 5 isolates were selected based on high α-amylase and glucoamylase activities and identified as Candida wangnamkhiaoensis, Hyphopichia pseudoburtonii (2 isolates), Wickerhamia sp., and Streptomyces drozdowiczii based on 26S rDNA and 16S rDNA sequencing. Wickerhamia sp. showed the highest ethanol production (30.4 g/L) with fermentation yield of 0.3 g ethanol/g starch. Then, a low cost starchy waste, potato peel waste (PPW) was used as a carbon source to produce ethanol by Wickerhamia sp. Finally, in order to obtain maximum ethanol production from PPW, a fermentation medium was statistically designed. The effect of various medium ingredients was evaluated initially by Plackett-Burman design (PBD), where malt extracts, tryptone, and KH₂PO₄ showed significantly positive effect (p value < 0.05). Using Response Surface Modeling (RSM), 40 g/L (dry basis) PPW and 25 g/L malt extract were found optimum and yielded 21.7 g/L ethanol. This study strongly suggests Wickerhamia sp. as a promising candidate for bioethanol production from starchy biomass, in particular, PPW through CBP.

Simultaneous saccharification and viscosity reduction of cassava pulp using a multi-component starch- and cell-wall degrading enzyme for bioethanol production

In this study, an efficient ethanol production process using simultaneous saccharification and viscosity reduction of raw cassava pulp with no prior high temperature pre-gelatinization/liquefaction step was developed using a crude starch- and cell wall-degrading enzyme preparation from Aspergillus aculeatus BCC17849. Proteomic analysis revealed that the enzyme comprised a complex mixture of endo- and exo-acting amylases, cellulases, xylanases, and pectina ses belonging to various glycosyl hydrolase families. Enzymatic hydrolysis efficiency was dependent on the initial solid loading in the reaction. Reduction in mixture viscosity was observed with a rapid decrease in complex viscosity from 3785 to 0.45 Pa s with the enzyme dosage of 2.19 mg/g on a dried weight basis within the first 2 h, which resulted from partial destruction of the plant cell wall fiber and degradation of the released starch granules by the enzymes as shown by scanning electron microscopy. Saccharification of cassava pulp at an initial solid of 16% (w/v) in a bench-scale bioreactor resulted in 736.4 mg glucose/g, which is equivalent to 82.92% glucose yield based on the total starch and glucan in the substrate, after 96 h at 40 °C. Simultaneous saccharification and fermentation of cassava pulp by Saccharomyces cerevisiae with the uncooked enzymatic process led to a final ethanol concentration of 6.98% w/v, equivalent to 96.7% theoretical yield based on the total starch and cellulose content. The results demonstrated potential of the enzyme for low-energy processing of cassava pulp in biofuel industry.

Advances in molecular engineering of carbohydrate-binding modules

Carbohydrate-binding modules (CBMs) are non-catalytic domains that are generally appended to carbohydrate-active enzymes. CBMs have a broadly conserved structure that allows recognition of a notable variety of carbohydrates, in both their soluble and insoluble forms, as well as in their alpha and beta conformations and with different types of bonds or substitutions. This versatility suggests a high functional plasticity that is not yet clearly understood, in spite of the important number of studies relating protein structure and function. Several studies have explored the flexibility of these systems by changing or improving their specificity toward substrates of interest. In this review, we examine the molecular strategies used to identify CBMs with novel or improved characteristics. The impact of the spatial arrangement of the functional amino acids of CBMs is discussed in terms of unexpected new functions that are not related to the original biological roles of the enzymes. Proteins 2017; 85:1602-1617. © 2017 Wiley Periodicals, Inc.

Development of enzyme technology for Aspergillus oryzae, A. sojae, and A. luchuensis, the national microorganisms of Japan

This paper describes the modern enzymology in Japanese bioindustries. The invention of Takadiastase by Jokiti Takamine in 1894 has revolutionized the world of industrial enzyme production by fermentation. In 1949, a new γ-amylase (glucan 1,4-α-glucosidase, EC 3.2.1.3) from A. luchuensis (formerly designated as A. awamori), was found by Kitahara. RNase T1 (guanyloribonuclease, EC 3.1.27.3) was discovered by Sato and Egami. Ando discovered Aspergillus nuclease S1 (single-stranded nucleate endonuclease, EC 3.1.30.1). Aspergillopepsin I (EC 3.4.23.18) from A. tubingensis (formerly designated as A. saitoi) activates trypsinogen to trypsin. Shintani et al. demonstrated Asp76 of aspergillopepsin I as the binding site for the basic substrate, trypsinogen. The new oligosaccharide moieties Man10GlcNAc2 and Man11GlcNAc2 were identified with α-1,2-mannosidase (EC 3.2.1.113) from A. tubingensis. A yeast mutant compatible of producing Man5GlcNAc2 human compatible sugar chains on glycoproteins was constructed. The acid activation of protyrosinase from A. oryzae at pH 3.0 was resolved. The hyper-protein production system of glucoamylase was established in a submerged culture.

Transcriptomic analysis of temperature responses of Aspergillus kawachii during barley koji production

The koji mold Aspergillus kawachii is used for making the Japanese distilled spirit shochu. During shochu production, A. kawachii is grown in solid-state culture (koji) on steamed grains, such as rice or barley, to convert the grain starch to glucose and produce citric acid. During this process, the cultivation temperature of A. kawachii is gradually increased to 40 °C and is then lowered to 30 °C. This temperature modulation is important for stimulating amylase activity and the accumulation of citric acid. However, the effects of temperature on A. kawachii at the gene expression level have not been elucidated. In this study, we investigated the effect of solid-state cultivation temperature on gene expression for A. kawachii grown on barley. The results of DNA microarray and gene ontology analyses showed that the expression of genes involved in the glycerol, trehalose, and pentose phosphate metabolic pathways, which function downstream of glycolysis, was downregulated by shifting the cultivation temperature from 40 to 30 °C. In addition, significantly reduced expression of genes related to heat shock responses and increased expression of genes related with amino acid transport were also observed. These results suggest that solid-state cultivation at 40 °C is stressful for A. kawachii and that heat adaptation leads to reduced citric acid accumulation through activation of pathways branching from glycolysis. The gene expression profile of A. kawachii elucidated in this study is expected to contribute to the understanding of gene regulation during koji production and optimization of the industrially desirable characteristics of A. kawachii.

Enzymatic conversions of starch

This article surveys methods for the enzymatic conversion of starch, involving hydrolases and nonhydrolyzing enzymes, as well as the role of microorganisms producing such enzymes. The sources of the most common enzymes are listed. These starch conversions are also presented in relation to their applications in the food, pharmaceutical, pulp, textile, and other branches of industry. Some sections are devoted to the fermentation of starch to ethanol and other products, and to the production of cyclodextrins, along with the properties of these products. Light is also shed on the enzymes involved in the digestion of starch in human and animal organisms. Enzymatic processes acting on starch are useful in structural studies of the substrates and in understanding the characteristics of digesting enzymes. One section presents the application of enzymes to these problems. The information that is included covers the period from the early 19th century up to 2009.

Decomposition of insoluble and hard-to-degrade animal proteins by enzyme E77 and its potential applications

Insoluble and hard-to-degrade animal proteins are group of troublesome proteins, such as collagen, elastin, keratin, and prion proteins that are largely generated by the meat industry and ultimately converted to industrial wastes. We analyzed the ability of the abnormal prion protein-degrading enzyme E77 to degrade insoluble and hard-to-degrade animal proteins including keratin, collagen, and elastin. The results indicate that E77 has a much higher keratinolytic activity than proteinase K and subtilisin. Maximal E77 keratinolytic activity was observed at pH 12.0 and 65 °C. E77 was also adsorbed by keratin in a pH-independent manner. E77 showed lower collagenolytic and elastinolytic specificities than proteinase K and subtilisin. Moreover, E77 treatment did not damage collagens in ovine small intestines but did almost completely remove the muscles. We consider that E77 has the potential ability for application in the processing of animal feedstuffs and sausages.

Designing industrial yeasts for the consolidated bioprocessing of starchy biomass to ethanol

Consolidated bioprocessing (CBP), which integrates enzyme production, saccharification and fermentation into a one step process, is a promising strategy for the effective ethanol production from cheap lignocellulosic and starchy materials. CBP requires a highly engineered microbial strain able to both hydrolyze biomass with enzymes produced on its own and convert the resulting simple sugars into high-titer ethanol. Recently, heterologous production of cellulose and starch-degrading enzymes has been achieved in yeast hosts, which has realized direct processing of biomass to ethanol. However, essentially all efforts aimed at the efficient heterologous expression of saccharolytic enzymes in yeast have involved laboratory strains and much of this work has to be transferred to industrial yeasts that provide the fermentation capacity and robustness desired for large scale bioethanol production. Specifically, the development of an industrial CBP amylolytic yeast would allow the one-step processing of low-cost starchy substrates into ethanol. This article gives insight in the current knowledge and achievements on bioethanol production from starchy materials with industrial engineered S. cerevisiae strains.

Loss of Aspergillus oryzae amyR function indirectly affects hemicellulolytic and cellulolytic enzyme production

Aspergillus oryzae AB390, a derivative of A. oryzae OR101, was found to be suitable for soy sauce production, yielding a product light brown in color. Compared to the parent strain, hemicellulase and cellulase activities in the mutant were higher; however, its amylase activity was found to be much lower. To determine the cause of these differences, the enzymatic profile change, as a function of the carbon source in submerged cultures, was examined. Amylase activity in AB390 was hardly detectable and not affected by the carbon source utilized. In the absence of starch where glucose could not be generated, hemicellulase and cellulase activities in both the parent and mutant were the same. A nonsense mutation was found in the upstream region of the putative transactivation domain of the transcriptional activator of the amylolytic genes, amyR in AB390. Complementation of AB390 with the wild-type amyR reduced hemicellulase and cellulase activities and increased amylase activity in soy sauce koji, the mold responsible for giving soy sauce. Northern analysis and two-dimensional (2-D) electrophoresis indicated that the unique enzymatic profile of AB390 was regulated transcriptionally. The results suggested that the loss of amyR function indirectly affected the production of hemicellulolytic and cellulolytic enzymes, likely through a carbon catabolite repression-mediated control.

The carbohydrate-binding module family 20--diversity, structure, and function

Starch-active enzymes often possess starch-binding domains (SBDs) mediating attachment to starch granules and other high molecular weight substrates. SBDs are divided into nine carbohydrate-binding module (CBM) families, and CBM20 is the earliest-assigned and best characterized family. High diversity characterizes CBM20s, which occur in starch-active glycoside hydrolase families 13, 14, 15, and 77, and enzymes involved in starch or glycogen metabolism, exemplified by the starch-phosphorylating enzyme glucan, water dikinase 3 from Arabidopsis thaliana and the mammalian glycogen phosphatases, laforins. The clear evolutionary relatedness of CBM20s to CBM21s, CBM48s and CBM53s suggests a common clan hosting most of the known SBDs. This review surveys the diversity within the CBM20 family, and makes an evolutionary comparison with CBM21s, CBM48s and CBM53s, discussing intrafamily and interfamily relationships. Data on binding to and enzymatic activity towards soluble ligands and starch granules are summarized for wild-type, mutant and chimeric fusion proteins involving CBM20s. Noticeably, whereas CBM20s in amylolytic enzymes confer moderate binding affinities, with dissociation constants in the low micromolar range for the starch mimic beta-cyclodextrin, recent findings indicate that CBM20s in regulatory enzymes have weaker, low millimolar affinities, presumably facilitating dynamic regulation. Structures of CBM20s, including the first example of a full-length glucoamylase featuring both the catalytic domain and the SBD, are summarized, and distinct architectural and functional features of the two SBDs and roles of pivotal amino acids in binding are described. Finally, some applications of SBDs as affinity or immobilization tags and, recently, in biofuel and in planta bioengineering are presented.

Recent advances in microbial raw starch degrading enzymes

Raw starch degrading enzymes (RSDE) refer to enzymes that can directly degrade raw starch granules below the gelatinization temperature of starch. These promising enzymes can significantly reduce energy and simplify the process in starch industry. RSDE are ubiquitous and produced by plants, animals, and microorganisms. However, microbial sources are the most preferred one for large-scale production. During the past few decades, RSDE have been studied extensively. This paper reviews the recent development in the production, purification, properties, and application of microbial RSDE. This is the first review on microbial RSDE to date.

Protein O-glycosylation in fungi: diverse structures and multiple functions

Protein glycosylation is essential for eukaryotic cells from yeasts to humans. When compared to N-glycosylation, O-glycosylation is variable in sugar components and the mode of linkages connecting the sugars. In fungi, secretory proteins are commonly mannosylated by protein O-mannosyltransferase (PMT) in the endoplasmic reticulum, and subsequently glycosylated by several glycosyltransferases in the Golgi apparatus to form glycoproteins with diverse O-glycan structures. Protein O-glycosylation has roles in modulating the function of secretory proteins by enhancing the stability and solubility of the proteins, by affording protection from protease degradation, and by acting as a sorting determinant in yeasts. In filamentous fungi, protein O-glycosylation contributes to proper maintenance of fungal morphology, hyphal development, and differentiation. This review describes recent studies of the structure and function of protein O-glycosylation in industrially and medically important fungi.

Solution structure of family 21 carbohydrate-binding module from Rhizopus oryzae glucoamylase

CBMs (carbohydrate-binding modules) function independently to assist carbohydrate-active enzymes. Family 21 CBMs contain approx. 100 amino acid residues, and some members have starchbinding functions or glycogen-binding activities. We report here the first structure of a family 21 CBM from the SBD (starch-binding domain) of Rhizopus oryzae glucoamylase (RoCBM21) determined by NMR spectroscopy. This CBM has a beta-sandwich fold with an immunoglobulin-like structure. Ligand-binding properties of RoCBM21 were analysed by chemical-shift perturbations and automated docking. Structural comparisons with previously reported SBDs revealed two types of topologies, namely type I and type II, with CBM20, CBM25, CBM26 and CBM41 showing type I topology, with CBM21 and CBM34 showing type II topology. According to the chemical-shift perturbations, RoCBM21 contains two ligand-binding sites. Residues in site II are similar to those found in the family 20 CBM from Aspergillus niger glucoamylase (AnCBM20). Site I, however, is embedded in a region with unique sequence motifs only found in some members of CBM21s. Additionally, docking of beta-cyclodextrin and malto-oligosaccharides highlights that side chains of Y83 and W47 (one-letter amino acid code) form the central part of the conserved binding platform in the SBD. The structure of RoCBM21 provides the first direct evidence of the structural features and the basis for protein-carbohydrate recognition from an SBD of CBM21.

A new clan of CBM families based on bioinformatics of starch-binding domains from families CBM20 and CBM21

Approximately 10% of amylolytic enzymes are able to bind and degrade raw starch. Usually a distinct domain, the starch-binding domain (SBD), is responsible for this property. These domains have been classified into families of carbohydrate-binding modules (CBM). At present, there are six SBD families: CBM20, CBM21, CBM25, CBM26, CBM34, and CBM41. This work is concentrated on CBM20 and CBM21. The CBM20 module was believed to be located almost exclusively at the C-terminal end of various amylases. The CBM21 module was known as the N-terminally positioned SBD of Rhizopus glucoamylase. Nowadays many nonamylolytic proteins have been recognized as possessing sequence segments that exhibit similarities with the experimentally observed CBM20 and CBM21. These facts have stimulated interest in carrying out a rigorous bioinformatics analysis of the two CBM families. The present analysis showed that the original idea of the CBM20 module being at the C-terminus and the CBM21 module at the N-terminus of a protein should be modified. Although the CBM20 functionally important tryptophans were found to be substituted in several cases, these aromatics and the regions around them belong to the best conserved parts of the CBM20 module. They were therefore used as templates for revealing the corresponding regions in the CBM21 family. Secondary structure prediction together with fold recognition indicated that the CBM21 module structure should be similar to that of CBM20. The evolutionary tree based on a common alignment of sequences of both modules showed that the CBM21 SBDs from alpha-amylases and glucoamylases are the closest relatives to the CBM20 counterparts, with the CBM20 modules from the glycoside hydrolase family GH13 amylopullulanases being possible candidates for the intermediate between the two CBM families.

Microbial starch-binding domain

Glucosidic bonds from different non-soluble polysaccharides such as starch, cellulose and xylan are hydrolyzed by amylases, cellulases and xylanases, respectively. These enzymes are produced by microorganisms. They have a modular structure that is composed of a catalytic domain and at least one non-catalytic domain that is involved in polysaccharide binding. Starch-binding modules are present in microbial enzymes that are involved in starch metabolism; these are classified into several different families on the basis of their amino acid sequence similarities. Such binding domains promote attachment to the substrate and increase its concentration at the active site of the enzyme, which allows microorganisms to degrade non-soluble starch. Fold similarities are better conserved than sequences; nevertheless, it is possible to notice two evolutionary clusters of microbial starch-binding domains. These domains have enormous potential as tags for protein immobilization, as well as for the tailoring of enzymes that play a part in polysaccharide metabolism.

Glucoamylase starch-binding domain of Aspergillus niger B1: molecular cloning and functional characterization

Carbohydrate-binding modules (CBMs) are protein domains located within a carbohydrate-active enzyme, with a discrete fold that can be separated from the catalytic domain. Starch-binding domains (SBDs) are CBMs that are usually found at the C-terminus in many amylolytic enzymes. The SBD from Aspergillus niger B1 (CMI CC 324262) was cloned and expressed in Escherichia coli as an independent domain and the recombinant protein was purified on starch. The A. niger B1 SBD was found to be similar to SBD from A. kawachii, A. niger var. awamori and A. shirusami (95-96% identity) and was classified as a member of the CBM family 20. Characterization of SBD binding to starch indicated that it is essentially irreversible and that its affinity to cationic or anionic starch, as well as to potato or corn starch, does not differ significantly. These observations indicate that the fundamental binding area on these starches is essentially the same. Natural and chemically modified starches are among the most useful biopolymers employed in the industry. Our study demonstrates that SBD binds effectively to both anionic and cationic starch.

Engineering of polyploid Saccharomyces cerevisiae for secretion of large amounts of fungal glucoamylase

We engineered Saccharomyces cerevisiae cells that produce large amounts of fungal glucoamylase (GAI) from Aspergillus awamori var. kawachi. To do this, we used the delta-sequence-mediated integration vector system and the heat-induced endomitotic diploidization method. delta-Sequence-mediated integration is known to occur mainly in a particular chromosome, and the copy number of the integration is variable. In order to construct transformants carrying the GAI gene on several chromosomes, haploid cells carrying the GAI gene on different chromosomes were crossed with each other. The cells were then allowed to form spores, which was followed by dissection. Haploid cells containing GAI genes on multiple chromosomes were obtained in this way. One such haploid cell contained the GAI gene on five chromosomes and exhibited the highest GAI activity (5.93 U/ml), which was about sixfold higher than the activity of a cell containing one gene on a single chromosome. Furthermore, we performed heat-induced endomitotic diploidization for haploid transformants to obtain polyploid mater cells carrying multiple GAI genes. The copy number of the GAI gene increased in proportion to the ploidy level, and larger amounts of GAI were secreted.

amyP, a reporter gene to study strain degeneration in Clostridium acetobutylicum ATCC 824

Clostridium acetobutylicum produces an extracellular alpha-amylase when grown on glucose as the sole carbon source. This enzyme was previously characterized from a biochemical point of view but its encoding gene was never identified. The 2283-bp amyP gene encodes a 83013-Da mature protein with an N-terminal domain that exhibits strong identity to the family 13 glycosyl hydrolases such as the Bacillus alpha-amylases. Transcriptional analysis revealed that amyP is transcribed in solventogenic but not in acidogenic chemostat cultures. These results are in agreement with the extracellular alpha-amylase activities indicating that the expression of amyP is regulated at the transcriptional level. amyP is located on the pSOL1 megaplasmid that carries all the genes involved in the final steps of solvent formation. Degeneration of C. acetobutylicum has been associated to the loss of pSOL1. We demonstrate here that amyP can be used as a reporter system to quantitatively follow this phenomenon.

Isolation of a raw starch-binding fragment from barley alpha-amylase

Barley alpha-amylase was purified by ammonium sulfate fraction, ion-exchange, ultrafiltration, and gel filtration to homogeneity. The purified enzyme was partially digested with trypsin, and the reaction mixture was applied to a cyclohepta-amylose epoxy Sepharose 6B column. Bound fragments were eluted by free cyclohepta-amylose, lyophilized, and separated on Tricine gels. Four fragments were shown to interact with beta-cyclodextrin. The fragment that could be identified on the gel with the lowest molecular weight (11 kDa) was electroblotted onto PVDF membrane for sequencing. The N-terminal sequence of this fragment was determined with the N-terminal amino acid corresponding to Ala283 in the whole protein. The trypsin cleavage was at Lys282/Ala283 and the C-terminal cleavage occurred at Lys354/Ile355 to give a fragment size of 11 kDa as estimated by SDS-PAGE. The fragment would be located at the C-terminal region, forming a majority of the antiparallel beta-sheets in domain C and the alpha7- and alpha8-helices of the (alpha/beta)8 domain.

Molecular cloning, characterization, and differential expression of a glucoamylase gene from the basidiomycetous fungus Lentinula edodes

The complete nucleotide sequence of putative glucoamylase gene gla1 from the basidiomycetous fungus Lentinula edodes strain L54 is reported. The coding region of the genomic glucoamylase sequence, which is preceded by eukaryotic promoter elements CAAT and TATA, spans 2,076 bp. The gla1 gene sequence codes for a putative polypeptide of 571 amino acids and is interrupted by seven introns. The open reading frame sequence of the gla1 gene shows strong homology with those of other fungal glucoamylase genes and encodes a protein with an N-terminal catalytic domain and a C-terminal starch-binding domain. The similarity between the Gla1 protein and other fungal glucoamylases is from 45 to 61%, with the region of highest conservation found in catalytic domains and starch-binding domains. We compared the kinetics of glucoamylase activity and levels of gene expression in L. edodes strain L54 grown on different carbon sources (glucose, starch, cellulose, and potato extract) and in various developmental stages (mycelium growth, primordium appearance, and fruiting body formation). Quantitative reverse transcription PCR utilizing pairs of primers specific for gla1 gene expression shows that expression of gla1 was induced by starch and increased during the process of fruiting body formation, which indicates that glucoamylases may play an important role in the morphogenesis of the basidiomycetous fungus.

Review: cyclodextrins and their interaction with amylolytic enzymes

This review is concerned with inhibition of amylases by cyclodextrins (cyclic maltooligosaccharides), the interaction that occurs between amylases and cyclodextrins and the application of cyclodextrin affinity chromatography in the purification of amylases. In many cases, amylases that are competitively inhibited by cyclodextrins can be purified by cyclodextrin affinity chromatography with the cyclodextrins interacting with the active site on such enzymes. Interestingly amylases that are not competitively inhibited by cyclodextrins may also be purified by cyclodextrin affinity chromatography. Therefore, cyclodextrin affinity chromatography can function in the purification of such amylolytic enzymes with the interaction occurring at a site removed from the active site. In such cases it appears that the cyclodextrin is interacting with an affinity site or binding site that is present on some amylolytic enzymes. It seems that certain similarities occur among the binding sites of such enzymes. Literature concerning amylases, and their subsequent purification using cyclodextrin affinity chromatography is reviewed and the fundamental basis of the interaction of the cyclodextrin with amylolytic enzymes is discussed here.

Identification and cloning of GCA1, a gene that encodes a cell surface glucoamylase from Candida albicans

Adherence of yeast cells of Candida albicans to human oesophageal cells is greater when cells are grown in 500 mM D-galactose in comparison to D-glucose at the same concentration. Moreover, a 190 kDa mannoprotein (MP190) from a yeast cell wall preparation is highly expressed when cells are grown in the presence of galactose but less so in glucose. We now report on the identification of the MP190 and the isolation of its encoding gene. MP190 was purified, and three internal peptides were isolated and sequenced. Each of the three peptides showed significant homology (65-85%) with a glucoamylase (GAM1) from the yeast, Schwanniomyces occidentalis. In order to isolate the C. albicans homologue of GAM1 (GCA1), we probed a genomic library with a 0.9-kb internal fragment of the S. occidentalis GAM1 and isolated a 2.3-kb clone that corresponded to the 5' region of the gene. Polymerase chain reaction (PCR) amplification was used to isolate the remainder of the open reading frame. GCA1 encodes a 946 amino acid protein containing three putative hydrophobic, membrane-spanning domains and 15 potential N-glycosylation sites. Both Gca1p and GAM1 are novel to the family of glycosyl hydrolases. Northern analysis indicated that GCA1 is transcribed to a greater extent in galactose than in sucrose or glucose. Also, using reverse transcriptase (RT)-PCR, we observed expression of GCA1 in a rat model of oral candidiasis, indicating that Gca1p is expressed during disease development.

Functional analysis of O-linked oligosaccharides in threonine/serine-rich region of Aspergillus glucoamylase by expression in mannosyltransferase-disruptants of yeast

The glaA gene encoding glucoamylase I (GAI) of Aspergillus awamori var. kawachi was heterologously expressed in mannosyltransferase mutants of Saccharomyces cerevisiae, in which the pmt1 gene and the kre2 gene were disrupted. The GAI enzymes expressed in these yeast mutant cells exhibited a lesser extent of O-glycosylation. Secretion of GAI expressed in the pmt1-disruptant and in the kre2-disruptant, respectively, was almost the same as that of GAI expressed in wild type (wt) strains. The number of O-linked mannose in GAI from wt yeast strain ranged in size from one (Man1) to five (Man5). On the other hand, the O-linked oligosaccharides of GAI from the pmt1-disruptant ranged in size from Man1 to Man4. Man5 was not detected and Man2-Man4 were reduced in proportion to the reduction of Man1. The O-linked oligosaccharides of GAI from the kre2-disruptant ranged from Man1 to Man4, and the molar amount of Man4 was reduced to 27.3%, compared to that of the wt strain. The hydrolyzing abilities for soluble starch and the adsorbing abilities on raw starch were comparable between both disruptants and wt strains. However, the digesting abilities for raw starch of the disruptants were decreased to 70% of those of the wt strains. Stabilities of GAI of the disruptants were reduced toward extreme pH and high temperature, compared to those of the wt strains. These results demonstrate that the O-linked oligosaccharides of GAI are responsible for the enzyme stability and activity toward insoluble substrates but not for secretion.

Expression and functional analysis of a hyperglycosylated glucoamylase in a parental host, Aspergillus awamori var. kawachi

A modified glucoamylase gene (glaA) with an extra Thr- and Ser-rich Gp-I domain (T. Semimaru, M. Goto, K. Furukawa, and S. Hayashida, Appl. Environ. Microbiol. 61:2885-2890, 1995) was introduced into a mutant parental host, Aspergillus awamori var. kawachi, in which the original glaA gene had been completely deleted and replaced with the hygromycin phosphotransferase gene. The modified glaA was successfully expressed and secreted. The modified glucoamylase possessed higher digestibility of raw corn starch and higher stabilities in response to heat and extreme pH.

Microbial hydrolysis of polysaccharides

Microorganisms are efficient degraders of starch, chitin, and the polysaccharides in plant cell walls. Attempts to purify hydrolases led to the realization that a microorganism may produce a multiplicity of enzymes, referred to as a system, for the efficient utilization of a polysaccharide. In order to fully characterize a particular enzyme, it must be obtained free of the other components of a system. Quite often, this proves to be very difficult because of the complexity of a system. This realization led to the cloning of the genes encoding them as an approach to eliminating other components. More than 400 such genes have been cloned and sequenced, and the enzymes they encode have been grouped into more than 50 families of related amino acid sequences. The enzyme systems revealed in this manner are complex on two quite different levels. First, many of the individual enzymes are complex, as they are modular proteins comprising one or more catalytic domains linked to ancillary domains that often include one or more substrate-binding domains. Second, the systems are complex, comprising from a few to 20 or more enzymes, all of which hydrolyze a particular substrate. Systems for the hydrolysis of plant cell walls usually contain more components than systems for the hydrolysis of starch and chitin because the cell walls contain several polysaccharides. In general, the systems produced by different microorganisms for the hydrolysis of a particular polysaccharide comprise similar enzymes from the same families.

Efficient production from Aspergillus niger of a heterologous protein and an individual protein domain, heavy isotope-labelled, for structure-function analysis

Aspergillus niger has been used successfully to secrete proteins labelled with 13C and/or 15N to a specific activity of > 99% for high resolution NMR analysis. In the case of a heterologous protein, hen egg-white lysozyme, 15N single-labelled and 13C, 15N double-labelled forms were secreted at yields of 100-200 mg l-1 by optimising the type of carbon source used and the ratio of carbon to nitrogen. Another protein, the glucoamylase starch-binding domain from A. niger, was also produced as the 15N single-labelled form at 20-40 mg l-1.

Expression in Aspergillus niger of the starch-binding domain of glucoamylase. Comparison with the proteolytically produced starch-binding domain

Glucoamylase 1 from Aspergillus niger is an economically important enzyme in many industrial processes. It hydrolyses granular starch and comprises two distinct domains, a catalytic and a starch-binding domain (SBD). We have transformed A. niger with an expression vector for the secretion of SBD for physico-chemical studies. This was achieved by introducing into the glucoamylase gene a short sequence encoding an endoproteolytic cleavage recognition site such that free SBD was secreted at yields up to 200 mg/l. Free SBD was also obtained by proteolytic digestion of full-length glucoamylase 1. Electrospray mass spectroscopy was used to determine the carbohydrate content of both SBDs. It revealed that the engineered one is more glycosylated: an average of three mannose residues compared to one for the proteolytically derived SBD. Sequencing results also suggest partial glycosylation for the three Thr residues involved (510, 511, 513). It is probable that the engineered SBD represents the true glycosylation level of the SBD in native glucoamylase. Binding of beta-cyclodextrin to the SBD was investigated. It was found that the stoichiometry and the spectral perturbation of Trp residues were identical for both SBDs, but the engineered SBD bound less strongly to the ligand. At high concentrations of beta-cyclodextrin relative to the estimated Kd values, the maximum absorbance changes were identical. The observed difference at low beta-cyclodextrin levels was probably due to the higher level of glycosylation of the expressed SBD. We conclude that the proteolytically derived and expressed starch binding domains both bind 2 mol beta-cyclodextrin/mol protein, but that the pattern of glycosylation and strength of binding are different.

Functional analysis of the threonine- and serine-rich Gp-I domain of glucoamylase I from Aspergillus awamori var. kawachi

Glucoamylase I (GAI) from Aspergillus awamori var. kawachi hydrolyzes raw starch efficiently and is composed of three functional domains: the amino-terminal catalytic GAI' domain (A-1 to V-469), the threonine- and serine-rich O-glycosylated Gp-I domain (A-470 to V-514), and the carboxy-terminal raw starch-binding Cp domain (A-515 to R-615). In order to investigate the role of the Gp-I domain, an additional repeat of Gp-I and internal deletions of the entire Gp-I sequence or parts of the Gp-I sequence were introduced within Gp-I. All mutant genes as well as the wild-type gene were inserted into a yeast-secretion vector, YEUp3H alpha, and expressed in Saccharomyces cerevisiae. Wild-type GAI expressed in yeast cells (GAY), GAGpI, having an extra Gp-I, and GA delta 470-493, lacking the A-470-to-T-493 sequences of Gp-I, were successfully secreted into the culture medium. On the other hand, GA delta 470-507, lacking A-470 to S-507, and GA delta GpI, lacking the entire Gp-I (A-470-to-V-514) sequence, failed to be secreted and remained in the yeast cells. The carbohydrate content of GAGpI was 1.2 times higher than that of GAY and 2.4 times higher than that of the original GAI. The raw starch digestibility of GAGpI was almost the same as that of GAY but was 1.5 times faster than that of GAI.(ABSTRACT TRUNCATED AT 250 WORDS)