Multiple attack and polarity of action of porcine pancreatic alpha-amylase

Maltogenic amylase: Its structure, molecular modification, and effects on starch and starch-based products

Maltogenic amylase (MAA) (EC3.2.1.133), a member of the glycoside hydrolase family 13 that mainly produces α-maltose, is widely used to extend the shelf life of bread as it softens bread, improves its elasticity, and preserves its flavor without affecting dough processing. Moreover, MAA is used as an improver in flour products. Despite its antiaging properties, the hydrolytic capacity and thermal stability of MAA can't meet the requirements of industrial application. However, genetic engineering techniques used for the molecular modification of MAA can alter its functional properties to meet application-specific requirements. This review briefly introduces the structure and functions of MAA, its application in starch modification, its effects on starch-based products, and its molecular modification to provide better insights for the application of genetically modified MAA in starch modification.

Molecular cloning and characterization of an alpha-amylase inhibitor (TkAAI) gene from Trichosanthes kirilowii Maxim

Trichosanthes kirilowii Maxim taxonomically belongs to the Cucurbitaceae family and Trichosanthes genus. Its whole fruit, fruit peel, seed and root are widely used in traditional Chinese medicines. A ribosome-inactivating protein with RNA N-glycosidase activity called Trichosanthrip was isolated and purified from the seeds of T. kirilowii in our recent previous research. To further explore the biological functions of Trichosanthrip, the cDNA of T. kirilowii alpha-amylase inhibitor (TkAAI) was cloned through rapid-amplification of cDNA ends and its sequence was analyzed. Also, the heterologous protein was expressed in Escherichia coli and its alpha-amylase activity was further measured under optimized conditions. The full-length cDNA of TkAAI was 613 bp. The speculated open reading frame sequence encoded 141 amino acids with a molecular weight of 16.14 kDa. Phylogenetic analysis demonstrated that the Alpha-Amylase Inhibitors Seed Storage domain sequence of TkAAI revealed significant evolutionary homology with the 2S albumin derived from the other plants in the Cucurbitaceae group. In addition, TkAAI was assembled into pET28a with eGFP to generate a prokaryotic expression vector and was induced to express in E. coli. The TkAAI-eGFP infusion protein was proven to exhibit alpha-amylase inhibitory activity against porcine pancreatic amylase in a suitable reaction system. Analysis of gene expression patterns proved that the relative expression level of TkAAI in seeds is highest. The results presented here forecasted that the TkAAI might play a crucial role during the development of T. kirilowii seeds and provided fundamental insights into the possibility of T. kirilowii derived medicine to treat diabetes related diseases.

Structural factors governing starch digestion and glycemic responses and how they can be modified by enzymatic approaches: A review and a guide

Starch is the most abundant glycemic carbohydrate in the human diet. Consumption of starch-rich food products that elicit high glycemic responses has been linked to the occurrence of noncommunicable diseases such as cardiovascular disease and diabetes mellitus type II. Understanding the structural features that govern starch digestibility is a prerequisite for developing strategies to mitigate any negative health implications it may have. Here, we review the aspects of the fine molecular structure that in native, gelatinized, and gelled/retrograded starch directly impact its digestibility and thus human health. We next provide an informed guidance for lowering its digestibility by using specific enzymes tailoring its molecular and three-dimensional supramolecular structure. We finally discuss in vivo studies of the glycemic responses to enzymatically modified starches and relevant food applications. Overall, structure-digestibility relationships provide opportunities for targeted modification of starch during food production and improving the nutritional profile of starchy foods.

Structures of two novel crystal forms of Aspergillus oryzae alpha amylase (taka-amylase)

The structures of Aspergillus oryzae α-amylase were determined in a tetragonal crystal, having one molecule as asymmetric unit, and a monoclinic crystal with two molecules as asymmetric unit. Both crystal forms were obtained from trace contaminants of an old commercial lipase preparation. Structures were determined and refined to 1.65 Å and 1.43 Å resolution respectively. The latter crystal has a non-crystallographic (NCS) twofold axis within the asymmetric unit. Glycosylation at Asn197 is evident, and in the tetragonal crystal can be seen to include three, partially disordered sugar residues following the initial N-acetyl glucosamine (NAG). Superposition of the tetragonal crystal model on the α-amylases from Bacillus subtilis (PDB:1BAG), pig pancreas (PDB:3L2L), and barley (PDB:1AMY), show a high degree of coincidence, particularly for the (β/α)₈-barrel domains, and especially within the active site. Using this structural agreement between amylases, we extrapolated the binding model of a six residue, limit dextrin found in pig pancreas α-amylase to the A. oryzae enzyme model, which predicts substrate interacting amino acid residues.

Catalytic efficiency of a multi-domain transglycosylating chitinase from Enterobacter cloacae subsp. cloacae (EcChi2) is influenced by polycystic kidney disease domains

Bacterial chitinases recruited multiple accessory domains for the conversion of recalcitrant polysaccharides to simple soluble sugars/amino sugars. Here, we report detailed properties of a multi-domain GH18 chitinase from Enterobacter cloacae subsp. cloacae (EcChi2) that preferred β-chitin as substrate. EcChi2 exhibited transglycosylation (TG) activity on oligomeric substrates from DP4-DP6. The high amount of DP2 is indicative of exo mode activity of EcChi2. We generated EcChi2 variants (truncated and fusion chimeras) and elucidated the role of catalytic and accessory domains. The catalytic efficiency of truncated GH18 and fusion chimera of GH18+ChBD1-ChBD2 decreased to 22 and 17-fold, respectively, than EcChi2, and lost the hydrolytic activity on polymeric substrates, except colloidal chitin. On the other hand, the catalytic activity of truncated PKD1-GH18-PKD2 on polymeric and oligomeric substrates was similar to EcChi2, suggesting that PKD domains are essential for increasing the rate of hydrolysis. Moreover, the truncated ChBD1-ChBD2 and fusion PKD1 + PKD2 participated in chitin-binding.

Novel cyclic thiourea derivatives of aminoalcohols at the presence of AlCl3 catalyst as potent α-glycosidase and α-amylase inhibitors: Synthesis, characterization, bioactivity investigation and molecular docking studies

The article is devoted to the targeted synthesis and study of cyclic thiourea and their various new derivatives as new organic compounds containing polyfunctional group in the molecule. First time the reaction of the corresponding synthesized pyrimidinethione with 1,2-epoxy-3-chlorpropane at the presence of AlCl₃ catalyst in 75-80% yield alkyl-1-(3-chloro-2-hydroxypropyl)-4-alkyl-6-phenyl-2-thioxo-1,2,5,6- tetrahydropyrimidine-5-carboxylates. In the next stage, new cyclic thiourea derivatives of aminoalcohols were synthesised from the reaction of chlorinated derivatives of pyrimidinethiones with single amines and their structures were investigated by spectroscopic methods. In this study, a series of novel compounds were tested towards some metabolic enzymes including α-glycosidase (α-Gly) and α-amylase (α-Amy) enzymes. Novel compounds showed K_is in ranging of 10.43 ± 0.94-111.37 ± 13.25 µM on α-glycosidase and IC₅₀ values in ranging of 14.38-106.51 µM on α-amylase. The novel cyclic thiourea derivatives of aminoalcohols had effective inhibition profiles against all tested metabolic enzymes. Binding affinity and inhibition mechanism of the most active compounds were detected with in silico studies and have shown that 2-Hydroxypropyl and butan-1-aminium moieties play a key role for inhibition of the enzymes.

Mobility of pectin methylesterase in pectin/cellulose gels is enhanced by the presence of cellulose and by its catalytic capacity

The pectin methylesterase action is usually studied in a homogeneous aqueous medium in the presence of a large excess of soluble substrate and water. However in the cell wall, the water content is much lower, the substrate is cross-linked with itself or with other polymers, and the enzyme has to diffuse through the solid matrix before catalysing the linkage breakdown. As plant primary cell walls can be considered as cellulose-reinforced hydrogels, this study investigated the diffusion of a fungal pectin methylesterase in pectin/cellulose gels used as cell wall-mimicking matrix to understand the impact of this matrix and its (micro) structure on the enzyme’s diffusion within it. The enzyme mobility was followed by synchrotron microscopy thanks to its auto-fluorescence after deep-UV excitation. Time-lapse imaging and quantification of intensity signal by image analysis revealed that the diffusion of the enzyme was impacted by at least two criteria: (i) only the active enzyme was able to diffuse, showing that the mobility was related to the catalytic ability, and (ii) the diffusion was improved by the presence of cellulose in the gel.

S-protected thiolated cyclodextrins as mucoadhesive oligomers for drug delivery

AIM

The purpose of this study was to develop a novel mucoadhesive thiolated and S-protected gamma cyclodextrin (γ-CD) with an intact ring backbone to assure a prolonged residence time at specific target sites.

METHOD

Thiolated γ-CD was generated through bromine substitution of its hydroxyl groups followed by replacement to thiol groups using thiourea. In the second step, thiol groups were protected by disulfide bond formation with 2-mercaptonicotinic acid (2-MNA).

RESULT

Thiolated γ-CD displayed 1385 ± 84 µmol thiol groups per gram of oligomer and the amount of MNA determined in the S-protected oligomer was 1153 ± 41 µmol per gram of oligomer. In-vitro screening of mucoadhesive properties of thiolated and S-protected γ-CD was done by two methods. Rheological investigation revealed the conjugates non-mucolytic with only a slight increase in viscosity of thiolated and S-protected γ-CD as compared to unmodified γ-CD, whereas mucoadhesive properties of the new thiolated and S-protected γ-CD performed on freshly excised porcine intestinal mucosa showed 44.4- and 50.9-fold improvement in mucoadhesion, respectively. The new conjugates did not show any cytotoxicity to Caco-2 cells even at a concentration of 1% (m/v) for 24 h. In addition, in-vitro studies of α-amylase degradation of γ-CD, γ-CD-SH and γ-CD-SS-MNA confirmed that all conjugates are biodegradable.

CONCLUSION

These outcomes predict that these new conjugates of γ-CD might provide a new favorable tool for drug delivery providing a prolonged residence time on mucosal surfaces.

Cloning, expression, and characterization of a porcine pancreatic α-amylase in Pichia pastoris

Pancreatic α-amylase (α-1, 4-glucan-4-glucanohydrolase, EC.3.2.1.1) plays a primary role in the intestinal digestion of feed starch and is often deficient in weanling pigs. The objective of this study was to clone, express, and characterize porcine pancreatic α-amylase (PPA). The full-length cDNA encoding the PPA was isolated from pig pancreas by RT-PCR and cloned into the pPICZαA vector. After the resultant pPICZαΑ-PPA plasmid was transferred into Pichia pastoris, Ni Sepharose affinity column was used to purify the over-expressed extracellular recombinant PPA protein (rePPA) that contains a His-tag to the C terminus and was characterized against the natural enzyme (α-amylase from porcine pancreas). The rePPA exhibited a molecular mass of approximately 58 kDa and showed optimal temperature (50 °C), optimal pH (7.5), K_m (47.8 mg/mL), and V_max (2,783 U/mg) similar to those of the natural enzyme. The recombinant enzyme was stable at 40 °C but lost 60% to 90% (P < 0.05) after exposure to heating at ≥50 °C for 30 min. The enzyme activity was little affected by Cu²⁺ or Fe³⁺, but might be inhibited (40% to 50%) by Zn²⁺ at concentrations in pig digesta. However, Ca²⁺ exhibited a dose-dependent stimulation of the enzyme activity. In conclusion, the present study successfully cloned the porcine pancreatic α-amylase gene and over-expressed the gene in P.pastoris as an extracellular, functional enzyme. The biochemical characterization of the over-produced enzyme depicts its potential and future improvement as an animal feed additive.

The GH26 β-mannanase RsMan26H from a symbiotic protist of the termite Reticulitermes speratus is an endo-processive mannobiohydrolase: heterologous expression and characterization

Symbiotic protists in the gut of termites are prominent natural resources for enzymes involved in lignocellulose degradation. Here we report expression, purification, and biochemical characterization of a glycoside hydrolase family 26 mannanase RsMan26H from the symbiotic protist of the lower termite, Reticulitermes speratus. Biochemical analysis of RsMan26H demonstrates that this enzyme is an endo-processive mannobiohydrolase producing mannobiose from oligo- and polysaccharides, followed by a minor accumulation of oligosaccharides larger than mannobiose. To our knowledge, this is the first report describing the unique mannobiohydrolase enzyme from the eukaryotic origin.

Chlorophyll composition and photochemical activity of photosystems detached from chloroplast grana and stroma lamellae

A stroma fraction that has photosystem 1 activity and grana lamellae fractions that have activities for both photosystems were isolated by differential centrifugation of a needle valve homogenate. Subsequent fractions, corresponding to photosystems 1 (F-1D) and 2 (F-2D) were isolated by digitonin treatment of the grana lamellae (P-10K) and compared with respect to their chlorophyll composition and electron transport activities.Fraction F-2D from grana lamellae having photosystem 2 activity is primarily active in photosystem 2 and contains only the four major forms of chlorophyll a with a predominance of chlorophyll a 677 nm. This fraction differs from the original grana membranes in the absence of the longwavelength form of chlorophyll a and in the widening of the absorption band of chlorophyll a 682 nm from 10.9 to 15.6 nm.Photosystem 1 particles from grana and stroma both have high photosystem 1 activity but differ from each other in the proportions of the four major forms of chlorophyll a. The short-wavelength forms of chlorophyll a and also chlorophyll b 650 nm in particles from grana lamellae comprise relatively more total area than these same forms in the particles from stroma. In addition, the fraction corresponding to photosystem 1 from grana lamellae is not shifted to the long-wavelength side of the main absorption maximum, as compared to the photosystem 2 particles from grana and the original grana membrane fraction; this is usually observed in fractions that have photosystem 1 activity. Furthermore, the longest wavelength form of chlorophyll a in the photosystem 1 particles from grana is at 700 nm, while in the same fraction from stroma, it is at 706 nm.The half-width of the four main forms of chlorophyll a and both forms of chlorophyll b in the photosystem 1 fraction from grana is narrower than that of the corresponding forms in the same fraction from stroma. This may indicate a different packing of pigment molecules that are aggregated on the surface of membranes of these two fractions.

X-ray crystallographic analyses of pig pancreatic alpha-amylase with limit dextrin, oligosaccharide, and alpha-cyclodextrin

Further refinement of the model using maximum likelihood procedures and reevaluation of the native electron density map has shown that crystals of pig pancreatic alpha-amylase, whose structure we reported more than 15 years ago, in fact contain a substantial amount of carbohydrate. The carbohydrate fragments are the products of glycogen digestion carried out as an essential step of the protein's purification procedure. In particular, the substrate-binding cleft contains a limit dextrin of six glucose residues, one of which contains both alpha-(1,4) and alpha-(1,6) linkages to contiguous residues. The disaccharide in the original model, shared between two amylase molecules in the crystal lattice, but also occupying a portion of the substrate-binding cleft, is now seen to be a tetrasaccharide. There are, in addition, several other probable monosaccharide binding sites. Furthermore, we have further reviewed our X-ray diffraction analysis of alpha-amylase complexed with alpha-cyclodextrin. alpha-Amylase binds three cyclodextrin molecules. Glucose residues of two of the rings superimpose upon the limit dextrin and the tetrasaccharide. The limit dextrin superimposes in large part upon linear oligosaccharide inhibitors visualized by other investigators. By comprehensive integration of these complexes we have constructed a model for the binding of polysaccharides having the helical character known to be present in natural substrates such as starch and glycogen.

Physical state of κ-carrageenan modulates the mode of action of κ-carrageenase from Pseudoalteromonas carrageenovora

Pseudoalteromonas carrageenovora κ-carrageenase is a glycoside hydrolase involved in the bioconversion of carrageenans. Carrageenans are sulfated galactans that are densely packed in red algal cell walls. Previous crystallographic investigations revealed that the active site of κ-carrageenase has a tunnel-shaped topology, suggesting a processive mode of action for this enzyme. To biochemically characterize the enzymatic depolymerization of κ-carrageenan, soluble and solid substrates (in both gel and powder forms) were incubated with P. carrageenovora κ-carrageenase. The average molecular mass of soluble carrageenan decreased rapidly, and all possible degradation products were observed, suggesting random degradation of κ-carrageenan. In contrast, as expected for a processive-type carrageenase, the average molecular mass of solid carrageenan decreased very slowly, and tetrasaccharide production was high. Interestingly, experimentally determined processivity was similar for gel and powder, suggesting that, in addition to an adapted catalytic site, the substrate must be in the solid state for κ-carrageenase processivity to operate, whatever the level of carrageenan ordering.

Human pancreatic digestive enzymes

A primary function of the pancreas is to produce digestive enzymes that are delivered to the small intestine for the hydrolysis of complex nutrients. Much of our understanding of digestive enzymes comes from studies in animals. New technologies and the availability of the sequence of the human genome allow for a critical review of older reports and assumptions based on animal studies. This report updates our understanding of human pancreatic digestive enzymes with a focus on new insights into the biology of human proteases, lipases and amylases.

Mechanism of action of theendo-(1 → 3)-α-glucanase MutAp from the mycoparasitic fungusTrichoderma harzianum

(1-->3)-alpha-glucanases catalyze the hydrolysis of fungal cell wall (1-->3)-alpha-glucan, and function during cell division of yeasts containing this cell wall component or act in mycoparasitic processes. Here, we characterize the mechanism of action of the (1-->3)-alpha-glucanase MutAp from the mycoparasitic fungus Trichoderma harzianum. We observed that MutAp releases predominantly beta-glucose upon hydrolysis of crystalline (1-->3)-alpha-glucan, indicating inversion of the anomeric configuration. After having identified (1-->3)-alpha-glucan tetrasaccharide as the minimal substrate for MutAp, we showed that reduced (1-->3)-alpha-glucan pentasaccharide is cleaved into a trisaccharide and a reduced disaccharide, demonstrating that MutAp displays endo-hydrolytic activity. We propose a model for the catalytic mechanism of MutAp, whereby the enzyme breaks an intrachain glycosidic linkage of (1-->3)-alpha-glucan, and then continues its hydrolysis towards the non-reducing end by releasing beta-glucose residues in a processive manner.

Bifidobacterium longum endogalactanase liberates galactotriose from type I galactans

A putative endogalactanase gene classified into glycoside hydrolase family 53 was revealed from the genome sequence of Bifidobacterium longum strain NCC2705 (Schell et al., Proc. Natl. Acad. Sci. USA 99:14422-14427, 2002). Since only a few endo-acting enzymes from bifidobacteria have been described, we have cloned this gene and characterized the enzyme in detail. The deduced amino acid sequence suggested that this enzyme was located extracellularly and anchored to the cell membrane. galA was cloned without the transmembrane domain into the pBluescript SK(-) vector and expressed in Escherichia coli. The enzyme was purified from the cell extract by anion-exchange and size exclusion chromatography. The purified enzyme had a native molecular mass of 329 kDa, and the subunits had a molecular mass of 94 kDa, which indicated that the enzyme occurred as a tetramer. The optimal pH of endogalactanase activity was 5.0, and the optimal temperature was 37 degrees C, using azurine-cross-linked galactan (AZCL-galactan) as a substrate. The K(m) and V(max) for AZCL-galactan were 1.62 mM and 99 U/mg, respectively. The enzyme was able to liberate galactotrisaccharides from (beta1-->4)galactans and (beta1-->4)galactooligosaccharides, probably by a processive mechanism, moving toward the reducing end of the galactan chain after an initial midchain cleavage. GalA's mode of action was found to be different from that of an endogalactanase from Aspergillus aculeatus. The enzyme seemed to be able to cleave (beta1-->3) linkages. Arabinosyl side chains in, for example, potato galactan hindered GalA.

Degradation of chitosans with chitinase B from Serratia marcescens

Family 18 chitinases such as chitinase B (ChiB) from Serratia marcescens catalyze glycoside hydrolysis via a mechanism involving the N-acetyl group of the sugar bound to the -1 subsite. We have studied the degradation of the soluble heteropolymer chitosan, to obtain further insight into catalysis in ChiB and to experimentally assess the proposed processive action of this enzyme. Degradation of chitosans with varying degrees of acetylation was monitored by following the size-distribution of oligomers, and oligomers were isolated and partly sequenced using (1)H-NMR spectroscopy. Degradation of a chitosan with 65% acetylated units showed that ChiB is an exo-enzyme which degrades the polymer chains from their nonreducing ends. The degradation showed biphasic kinetics: the faster phase is dominated by cleavage on the reducing side of two acetylated units (occupying subsites -2 and -1), while the slower kinetic phase reflects cleavage on the reducing side of a deacetylated and an acetylated unit (bound to subsites -2 and -1, respectively). The enzyme did not show preferences with respect to acetylation of the sugar bound in the +1 subsite. Thus, the preference for an acetylated unit is absolute in the -1 subsite, whereas substrate specificity is less stringent in the -2 and +1 subsites. Consequently, even chitosans with low degrees of acetylation could be degraded by ChiB, permitting the production of mixtures of oligosaccharides with different size distributions and chemical composition. Initially, the degradation of the 65% acetylated chitosan almost exclusively yielded oligomers with even-numbered chain lengths. This provides experimental evidence for a processive mode of action, moving the sugar chain two residues at a time. The results show that nonproductive binding events are not necessarily followed by substrate release but rather by consecutive relocations of the sugar chain.

On the mechanism of α-amylase

Two inhibitors, acarbose and cyclodextrins (CD), were used to investigate the active site structure and function of barley alpha-amylase isozymes, AMY1 and AMY2. The hydrolysis of DP 4900-amylose, reduced (r) DP18-maltodextrin and maltoheptaose (catalysed by AMY1 and AMY2) was followed in the absence and in the presence of inhibitor. Without inhibitor, the highest activity was obtained with amylose, kcat/Km decreased 103-fold using rDP18-maltodextrin and 10(5) to 10(6)-fold using maltoheptaose as substrate. Acarbose is an uncompetitive inhibitor with inhibition constant (L1i) for amylose and maltodextrin in the micromolar range. Acarbose did not bind to the active site of the enzyme, but to a secondary site to give an abortive ESI complex. Only AMY2 has a second secondary binding site corresponding to an ESI2 complex. In contrast, acarbose is a mixed noncompetitive inhibitor of maltoheptaose hydrolysis. Consequently, in the presence of this oligosaccharide substrate, acarbose bound both to the active site and to a secondary binding site. alpha-CD inhibited the AMY1 and AMY2 catalysed hydrolysis of amylose, but was a very weak inhibitor compared to acarbose.beta- and gamma-CD are not inhibitors. These results are different from those obtained previously with PPA. However in AMY1, as already shown for amylases of animal and bacterial origin, in addition to the active site, one secondary carbohydrate binding site (s1) was necessary for activity whereas two secondary sites (s1 and s2) were required for the AMY2 activity. The first secondary site in both AMY1 and AMY2 was only functional when substrate was bound in the active site. This appears to be a general feature of the alpha-amylase family.

Biochemical characterization of Aspergillus awamori exoinulinase: substrate binding characteristics and regioselectivity of hydrolysis

1H-NMR analysis was applied to investigate the hydrolytic activity of Aspergillus awamori inulinase. The obtained NMR signals and deduced metabolite pattern revealed that the enzyme cleaves off only fructose from inulin and does not possess transglycosylating activity. Kinetics for the enzyme hydrolysis of inulooligosaccharides with different degree of polymerization (d.p.) were recorded. The enzyme hydrolyzed both beta2,1- as well as beta2,6-fructosyl linkages in fructooligosaccharides. From the k(cat)/K(m) ratios obtained with inulooligosaccharides with d.p. from 2 to 7, we deduce that the catalytic site of the inulinase contains at least five fructosyl-binding sites and can be classified as exo-acting enzyme. Product analysis of inulopentaose and inulohexaose hydrolysis by the Aspergillus inulinase provided no evidence for a possible multiple-attack mode of action, suggesting that the enzyme acts exclusively as an exoinulinase.

Subsite mapping of human salivary alpha-amylase and the mutant Y151M

This study characterizes the substrate-binding sites of human salivary alpha-amylase (HSA) and its Y151M mutant. It describes the first subsite maps, namely, the number of subsites, the position of cleavage sites and apparent subsite energies. The product pattern and cleavage frequencies were determined by high-performance liquid chromatography, utilizing a homologous series of chromophore-substituted maltooligosaccharides of degree of polymerization 3-10 as model substrates. The binding region of HSA is composed of four glycone and three aglycone-binding sites, while that of Tyr151Met is composed of four glycone and two aglycone-binding sites. The subsite maps show that Y151M has strikingly decreased binding energy at subsite (+2), where the mutation has occurred (-2.6 kJ/mol), compared to the binding energy at subsite (+2) of HSA (-12.0 kJ/mol).

Bacillus macerans cyclomaltodextrin glucanotransferase transglycosylation reactions with different molar ratios of D-glucose and cyclomaltohexaose

It was found that Bacillus macerans cyclomaltodextrin glucanotransferase (CGTase) reacts with cyclomaltohexaose (alpha-cyclodextrin, alpha-CD) to give a series of cyclomaltooligosaccharides (cyclomaltodextrins, CDs), having seven to more than 20 D-glucose residues and maltooligosaccharides (maltodextrins, MDs) from G5 to G12+. When D-glucose (Glc) was added to the alpha-CD at very low molar ratios (1:100) of Glc to alpha-CD, the predominant products (95%) were CDs, some of which were macrocyclic MDs with 20-60 D-glucose residues, along with MDs that also had high molecular weights, containing 10-75 D-glucose residues and gave a blue iodine-iodide color. As the molar ratio of Glc to alpha-CD was increased, the amount of CDs progressively decreased and MDs proportionately increased in the range of G2-G12. At 25 mM alpha-CD and Glc to alpha-CD molar ratio of 1:1, a 75% yield of MDs, G1-G12, each in approximately equal amounts, was obtained; and at 20 mM and a 5:1 ratio, a 97% yield of MDs, G2-G9, was obtained but in unequal amounts. At higher ratios (10:1), the CDs completely disappeared, and at very high ratios (50:1 to 100:1) only low-molecular-weight MDs, G2-G4, were formed.

Subsite mapping of the binding region of alpha-amylases with a computer program

A computer program has been evaluated for subsite map calculations of depolymerases. The program runs in windows and uses the experimentally determined bond cleavage frequencies (BCFs) for determination of the number of subsites, the position of the catalytic site and for calculation of subsite binding energies. The apparent free energy values were optimized by minimization of the differences of the measured and calculated BCF data. The program called suma (SUbsite Mapping of alpha-Amylases) is freely available for research and educational purposes via the Internet (E-mail: gyemant@tigris.klte.hu). The advantages of this program are demonstrated through alpha-amylases of different origin, e.g. porcine pancreatic alpha-amylase (PPA) studied in our laboratory, in addition to barley and rice alpha-amylases published in the literature. Results confirm the popular 'five subsite model' for PPA with three glycone and two aglycone binding sites. Calculations for barley alpha-amylase justify the '6 + 2 + (1) model' prediction. The binding area of barley alpha-amylase is composed of six glycone, two aglycone binding sites followed by a barrier subsite at the reducing end of the binding site. Calculations for rice alpha-amylase represent an entirely new map with a '(1) + 2 + 5 model', where '(1)' is a barrier subsite at the nonreducing end of the binding site and there are two glycone and five aglycone binding sites. The rice model may be reminiscent of the action of the bacterial maltogenic amylase, that is, suggesting an exo-mechanism for this enzyme.

Reactions of alpha amylases with starch granules in aqueous suspension giving products in solution and in a minimum amount of water giving products inside the granule

Porcine pancreatic alpha amylase (PPA) and Bacillus amyloliquefaciens alpha amylase (BAA) were allowed to react with starch granules from maize, waxy maize, amylomaize-7, and potato in an aqueous suspension with a starch to water ratio of 1:10 and in a minimum of water with a starch to water ratio of 1:1. Quantitative amounts of the maltodextrin products were determined by TLC and scanning densitometry. The two alpha amylases gave different products that were characteristic of their unique action patterns. The percent conversion differed for the different kinds of starches and for the two kinds of reaction conditions. Maize and waxy maize starches were converted into about twice as much maltodextrins than were amylomaize-7 and potato starches by both enzymes and under both reaction conditions. The aqueous suspension gave much greater conversion into maltodextrins than did the minimum water condition. BAA gave 3-14% greater conversion of the granules into maltodextrins than did PPA, with the exception of potato starch.

Changing a single amino acid residue switches processive and non-processive behavior of Aspergillus niger endopolygalacturonase I and II

Processivity, also known as multiple attack on a single chain, is a feature commonly encountered only in enzymes in which the substrate binds in a tunnel. However, of the seven Aspergillus niger endopolygalacturonases, which have an open substrate binding cleft, four enzymes show processive behavior, whereas the other endopolygalacturonases are randomly acting enzymes. In a previous study (Benen, J.A.E., Kester, H.C.M., and Visser, J. (1999) Eur. J. Biochem. 259, 577-585) we proposed that the high affinity for the substrate of subsite -5 of processive endopolygalacturonase I constitutes the origin of the multiple attack behavior. Based on primary sequence alignments of A. niger endopolygalacturonases and three-dimensional structure analysis of endopolygalacturonase II, an arginine residue was identified in the processive enzymes at a position commensurate with subsite -5, whereas a serine residue was present at this position in the non-processive enzymes. In endopolygalacturonase I mutation R95S was introduced, and in endopolygalacturonase II mutation S91R was introduced. Product progression analysis on polymer substrate and bond cleavage frequency studies using oligogalacturonides of defined chain length for the mutant enzymes revealed that processive/non-processive behavior is indeed interchangeable by one single amino acid substitution at subsite -5, Arg-->Ser or Ser-->Arg.

Characterization of a novel endopolygalacturonase from Aspergillus niger with unique kinetic properties

We isolated and characterized a new type of endopolygalacturonase (PG)-encoding gene, pgaD, from Aspergillus niger. The primary structure of PGD differs from that of other A. niger PGs by a 136 amino acid residues long N-terminal extension. Biochemical analysis demonstrated extreme processive behavior of the enzyme on oligomers longer than five galacturonate units. Furthermore, PGD is the only A. niger PG capable of hydrolyzing di-galacturonate. It is tentatively concluded that the enzyme is composed of four subsites. The physiological role of PGD is discussed.

Fungal polygalacturonases exhibit different substrate degradation patterns and differ in their susceptibilities to polygalacturonase-inhibiting proteins

Polygalacturonic acid (PGA) was hydrolyzed by polygalacturonases (PGs) purified from six fungi. The oligogalacturonide products were analyzed by HPAEC-PAD (high performance anion exchange chromatography-pulsed amperimetric detection) to assess their relative amounts and degrees of polymerization. The abilities of the fungal PGs to reduce the viscosity of a solution of PGA were also determined. The potential abilities of four polygalacturonase-inhibiting proteins (PGIPs) from three plant species to inhibit or to modify the hydrolytic activity of the fungal PGs were determined by colorimetric and HPAEC-PAD analyses, respectively. Normalized activities of the different PGs acting upon the same substrate resulted in one of two distinct oligogalacturonide profiles. Viscometric analysis of the effect of PGs on the same substrate also supports two distinct patterns of cleavage. A wide range of susceptibility of the various PGs to inhibition by PGIPs was observed. The four PGs that were inhibited by all PGIPs tested exhibited an endo/exo mode of substrate cleavage, while the three PGs that were resistant to inhibition by one or more of the PGIPs proceed by a classic endo pattern of cleavage.

Enzymatic generation of binary block-copolymeric structures: mathematical analysis based on triad frequencies evaluated by NMR

A mathematical model is derived for describing a multiple-attack pathway for enzymatic generation of block structure in binary linear copolymers having initially a randomized sequential structure. The model is based on sequential information in terms of copolymer monads, diads, and triads estimated by nmr spectroscopy, and is applicable to enzymes attacking next to a reacted unit in the polymer chains. Then the block distribution of unreacted units remains constant and explicit relationships are provided. The probability of triad frequencies as a function of monads, i.e., progress curve of enzyme copolymer sequential structure, allows us to characterize the enzymatic mode of attack independently of enzyme kinetics. The produced fractions of heterogeneous triads centered by reacted units are shown to be affected, to a large extent, by the degree of multiple attack (d) entering into the formula as a variable parameter. The single-chain, d = infinity, and multiple-chain mechanisms, d = 1, representing the two extremes of the treated mechanism, are very clearly discriminated.

Kinetic characterization of Aspergillus niger N400 endopolygalacturonases I, II and C

Endopolygalacturonases I, II and C isolated from recombinant Aspergillus niger strains were characterized with respect to pH optimum, activity on polygalacturonic acid and mode of action and kinetics on oligogalacturonates of different chain length (n = 3-7). Apparent Vmax values using polygalacturonate as a substrate at the pH optimum, pH 4.1, were calculated as 13.8 mukat.mg-1, 36.5 mukat.mg-1 and 415 nkat.mg-1 for endopolygalacturonases I, II and C, respectively. K(m) values were < 0.15 mg.mL-1 for all three enzymes. Product progression analysis using polygalacturonate as a substrate revealed a random cleavage pattern for all three enzymes and suggested processive behavior for endopolygalacturonases I and C. This result was confirmed by analysis of the mode of action using oligogalacturonates. Processivity was observed when the degree of polymerization of the substrate exceeded 5 or 6 for endopolygalacturonase I and endopolygalacturonase C, respectively. The bond-cleavage frequencies obtained for the hydrolysis of the oligogalacturonates were used to assess subsite maps. The maps indicate that the minimum number of subsites is seven for all three enzymes. Using pectins of various degrees of esterification, it was shown that endopolygalacturonase II is the most sensitive to the presence of methyl esters. Like endopolygalacturonase II, endopolygalacturonases I, C and E, which was also included in this part of the study, preferred the non-esterified pectate. Additional differences in substrate specificity were revealed by analysis of the reaction products of hydrolysis of a mixture of pectate lyase-generated delta 4,5-unsaturated oligogalacturonates of degree of polymerization 4-8. Whereas endopolygalacturonase I showed a strong preference for generating the delta 4,5-unsaturated dimer, with endopolygalacturonase II the delta 4,5-unsaturated trimer accumulated, indicating further differences in substrate specificity. For endopolygalacturonases C and E both the delta 4,5-unsaturated dimer and trimer were observed, although in different ratios.

A monte carlo simulation of the depolymerization of linear homopolymers by endo-enzymes exhibiting random-attack probability and single-attack mechanism: application to the (1-->3), (1-->4)-beta-D-glucan/endo-(1-->3),(1-->4)-beta-D-glucanase system

A Monte Carlo simulation of the depolymerization of linear homopolymers by specific endo-enzymes exhibiting random-attack probability and a single-attack mechanism has been developed. The program simulates the "real" depolymerization versus time of a polydisperse sample of substrate by a specific endo-enzyme. Given the initial mass distribution and concentration of the substrate, the initial concentration of the enzyme, and its Michaelis-Menten constant, the program simulates the evolution of the mass distribution of the substrate with the depolymerization time. When tested against experimental data from the depolymerization of barley (1-->3),(1-->4)-beta-D-glucan by malt endo-(1-->3), (1-->4)-beta-D-glucanase, monitored using the Calcofluor-FIA method with fluorescent detection, excellent results were obtained. Copyright 1998 John Wiley & Sons, Inc.

Analysis of molecular size distributions of cellulose molecules during hydrolysis of cellulose by recombinant Cellulomonas fimi beta-1,4-glucanases

Four beta-1,4-glucanases (cellulases) of the cellulolytic bacterium Cellulomonas fimi were purified from Escherichia coli cells transformed with recombinant plasmids. Previous analyses using soluble substrates had suggested that CenA and CenC were endoglucanases while CbhA and CbhB resembled the exo-acting cellobiohydrolases produced by cellulolytic fungi. Analysis of molecular size distributions during cellulose hydrolysis by the individual enzymes confirmed these preliminary findings and provided further evidence that endoglucanase CenC has a more processive hydrolytic activity than CenA. The significant differences between the size distributions obtained during hydrolysis of bacterial microcrystalline cellulose and acid-swollen cellulose can be explained in terms of the accessibility of beta-1,4-glucan chains to enzyme attack. Endoglucanases and cellobiohydrolases were much more easily distinguished when the acid-swollen substrate was used.

Differential patterns of activity displayed by two exo-beta-1,3-glucanases associated with the Aspergillus fumigatus cell wall

Two exo-beta-1,3-glucanases (herein designated exoG-I and exoG-II) were isolated from the cell wall autolysate of the filamentous fungus Aspergillus fumigatus and purified by ion-exchange, hydrophobic-interaction, and gel filtration chromatographies. Molecular masses estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration chromatography were 82 kDa for the monomeric exoG-I and 230 kDa for the dimeric exoG-II. exoG-I and exoG-II were glycosylated, and N glycans accounted, respectively, for 2 and 44 kDa. Their pH optimum is 5.0. Their optimum temperatures are 55 degrees C for exoG-I and 65 degrees C for exoG-II. By a sensitive colorimetric method and high-performance anion-exchange chromatography for product analysis, two patterns of exo-beta-1,3-glucanase activities were found. The 230-kDa exoG-II enzyme acts on p-nitrophenyl-beta-D-glucoside, beta-1,6-glucan, and beta-1,3-glucan. This activity, which retains the anomeric configuration of glucose released, presented a multichain pattern of attack of the glucan chains and a decrease in the maximum initial velocity (Vm) with the increasing size of the substrate. In contrast, the 82-kDa exoG-I, which inverts the anomeric configuration of the glucose released, hydrolyzed exclusively the beta-1,3-glucan chain with a minimal substrate size of 4 glucose residues. This enzyme presented a repetitive-attack pattern, characterized by an increase in Vm with an increase in substrate size and by a degradation of the glucan chain until it reached laminaritetraose, the limit substrate size. The 82-kDa exoG-I and 230-kDa exoG-II enzymes correspond to a beta-1,3-glucan-glucohydrolase (EC 3.2.1.58) and to a beta-D-glucoside-glucohydrolase (EC 3.2.1.21), respectively. The occurrence and functions of these two classes of exo-beta-1,3-glucanases in other fungal species are discussed.

Action pattern of porcine pancreatic alpha-amylase on three different series of beta-maltooligosaccharide glycosides

A technique for the investigation of the action pattern of porcine pancreatic amylase (PPA) has been developed by utilising as model substrates 2-chloro-4-nitrophenyl (CNP) and 4-nitrophenyl (NP) beta-glycosides of maltooligosaccharides of dp 4-8 and some NP derivatives modified at the nonreducing end with a 4,6-O-benzylidene (Bnl) group. The action pattern was investigated by the method of product analysis, using an HPLC method. The product pattern and cleavage frequency was very similar in the CNP- and NP-oligomers and showed that the glucopyranose residue could be replaced by the aglycon group. Modification of the nonreducing end of NP glycosides to give a 4,6-O-benzylidene-D-glucopyranosyl group indicated a favourable interaction between the Bnl group and the subsites (-3) and (-5) but an unfavourable one with subsite (-4), which resulted in a clear shift in the product pattern. The results obtained with the digestion of the benzylidene-protected substrates confirm a multiple attack mechanism for PPA.