On the mechanism of α-amylase

Analysis of the mechanism of resistance to enzymatic hydrolysis of RS-5 resistant starch

RS-5 refers to the resistant starch formed by complexation of starch molecules with other molecules. In this study, the molecular mechanism of RS-5 was analysed. First, it was found, when α-amylase acted on the starch-lipid complexes, the glucose residues involved in complexation cannot be hydrolyzed by α-amylase, while the glucose residues not directly involved in complexation can be hydrolyzed. Second, lipid molecules are not necessary for the formation of RS-5 and can be replaced with small peptides or decanal molecules. Considering the multiple health hazards that may result from excessive lipid intake, small peptides composed of essential amino acids may be more desirable materials for RS-5 preparation. Third, starch-lipid complexes had strong interactions with α-amylase, which provides evidence in support of the sliding continuum hydrolysis hypothesis of α-amylase. These results revealed the mechanism of RS-5 at the molecular level, which provides a reference for the production and research of RS-5.

Optimization of Ultrasound-Assisted Deep Eutectic Solvent Extraction, Characterization, and Bioactivities of Polysaccharide from Pericarpium Citri Reticulatae

The ultrasonic-assisted deep eutectic solvent method was used to extract the polysaccharides of Pericarpium Citri Reticulatae (PCRP), and the ultrasound-assisted DES extraction process was optimized by Box-Behnken response surface test using the extraction rate of the PCRP as an index; the in vitro activities of purified the PCRP(PCRPs-1) were investigated by determining the scavenging rate of DPPH• and ABTS•+ as well as by enzyme inhibition assay. The monosaccharide composition was analyzed by HPLC. The best process conditions for response surface optimization were a material-liquid ratio of 1:37 g/mL, water content of 44%, time of 89 min, and power of 320 W. The polysaccharide extraction rate was measured to be 5.41%, which was well optimized when compared with that of the ordinary aqueous extraction method of 3.92%. By α-glucosidase and α-amylase inhibition activity test, it showed that the PCRPs-1 had hypoglycemic activity. The DPPH radical scavenging activity test and ABTS + scavenging activity test indicated that the PCRPs-1 had good biological activity. Analysis of the monosaccharide fractions showed that the PCRPs-1 consisted of mannose, rhamnose, glucuronic acid, galacturonic acid, glucose, galactose, xylose, and arabinose, with molar ratios of 1:39.24:4.41:8.91:7.83:86.00:1.02:9.17. The activity studies showed that PCRPs-1 possessed certain hypoglycaemic and antioxidant activities.

Analysis of the relationship between starch molecular conformation and enzymatic hydrolysis efficiency

Resistant starch (RS) is important in controlling diabetes. The primary objective of this study is to examine the impact of molecular conformation on the enzymatic hydrolysis efficiency of starch by α-amylase. And the interactions between starch molecules with different conformations and α-amylase were analysed by using molecule dynamics simulation and molecular docking. It was found, the natural conformational starch molecule was hydrolysed from the middle of the starch chain by α-amylase, producing polysaccharides. The bent PS-conformational starch molecules with multiple O2-O3 intramolecular hydrogen bonds produced by high-pressure was hydrolysed from the head of the starch chain to produce glucose, which is not conducive to RS formation. The stretched H-conformation without intramolecular hydrogen bonds produced by heat treatment was not hydrolysed by α-amylase. However, it occupied the active groove and formed strong interactions with α-amylase, which prevented other starch molecules from binding to α-amylase, thus reducing hydrolysis efficiency. Moreover, the total interaction energies between the three starch molecules and α-amylase were approximately 78 kJ/mol. And several hydrogen bonds were formed between the starch molecules and α-amylase, which provides evidence for the continuous sliding hydrolysis hypothesis of α-amylase. Moreover, these results provide an important reference for elucidating the mechanism of RS formation.

Exploration of the Transglycosylation Activity of Barley Limit Dextrinase for Production of Novel Glycoconjugates

A few α-glucan debranching enzymes (DBEs) of the large glycoside hydrolase family 13 (GH13), also known as the α-amylase family, have been shown to catalyze transglycosylation as well as hydrolysis. However, little is known about their acceptor and donor preferences. Here, a DBE from barley, limit dextrinase (HvLD), is used as a case study. Its transglycosylation activity is studied using two approaches; (i) natural substrates as donors and different p-nitrophenyl (pNP) sugars as well as different small glycosides as acceptors, and (ii) α-maltosyl and α-maltotriosyl fluorides as donors with linear maltooligosaccharides, cyclodextrins, and GH inhibitors as acceptors. HvLD showed a clear preference for pNP maltoside both as acceptor/donor and acceptor with the natural substrate pullulan or a pullulan fragment as donor. Maltose was the best acceptor with α-maltosyl fluoride as donor. The findings highlight the importance of the subsite +2 of HvLD for activity and selectivity when maltooligosaccharides function as acceptors. However, remarkably, HvLD is not very selective when it comes to aglycone moiety; different aromatic ring-containing molecules besides pNP could function as acceptors. The transglycosylation activity of HvLD can provide glycoconjugate compounds with novel glycosylation patterns from natural donors such as pullulan, although the reaction would benefit from optimization.

Designing starch derivatives with desired structures and functional properties via rearrangements of glycosidic linkages by starch-active transglycosylases

Modification of starch by transglycosylases from glycoside hydrolase families has attracted much attention recently; these enzymes can produce starch derivatives with novel properties, i.e. processability and functionality, employing highly efficient and safe methods. Starch-active transglycosylases cleave starches and transfer linear fragments to acceptors introducing α-1,4 and/or linear/branched α-1,6 glucosidic linkages, resulting in starch derivatives with excellent properties such as complexing and resistance to digestion characteristics, and also may be endowed with new properties such as thermo-reversible gel formation. This review summarizes the effects of variations in glycosidic linkage composition on structure and properties of modified starches. Starch-active transglycosylases are classified into 4 groups that form compounds: (1) in cyclic with α-1,4 glucosidic linkages, (2) with linear chains of α-1,4 glucosidic linkages, (3) with branched α-1,6 glucosidic linkages, and (4) with linear chains of α-1,6 glucosidic linkages. We discuss potential processability and functionality of starch derivatives with different linkage combinations and structures. The changes in properties caused by rearrangements of glycosidic linkages provide guidance for design of starch derivatives with desired structures and properties, which promotes the development of new starch products and starch processing for the food industry.

Fucoidan Regulates Starch Digestion: In Vitro and Mechanistic Study

Bread is a high glycemic index (GI) food with high amounts of readily digestible carbohydrates. Fucoidan refers to a group of sulfated polysaccharides isolated from brown seaweed that has been gaining traction for its many functional properties, including its ability to inhibit starch hydrolases. In this study, fucoidan was added into bread to lower the glycemic index of bread. Fucoidan fortification at 3.0% reduced the starch digestion rate of baked bread by 21.5% as compared to control baked bread. This translated to a 17.7% reduction in the predicted GI (pGI) with 3.0% of fucoidan. Fucoidan was retained in the bread after baking. Although the in vitro bioavailability of fucoidan was negligible, the in vitro bioaccessibility of fucoidan was high, at 77.1–79.8%. This suggested that although fucoidan may not be absorbed via passive diffusion, there is potential for the fucoidan to be absorbed via other modes of absorption. Thus, there is a potential for the use of fucoidan as a functional ingredient in bread to reduce the glycemic potential of bread.

Over-Expression of a Wheat Late Maturity Alpha-Amylase Type 1 Impact on Starch Properties During Grain Development and Germination

The hydrolysis of starch is a complex process that requires synergistic action of multiple hydrolytic enzymes, including α-amylases. Wheat over-expression of TaAmy1, driven by seed specific promoter, resulted in a 20- to 230-fold total α-amylase activity in mature grains. Ectopic expression of TaAmy1 showed a significant elevated α-amylase activity in stem and leaf without consequences on transitory starch. In mature grain, overexpressed TaAMY1 was mainly located in the endosperm with high expression of TaAmy1. This is due to early developing grains having effect on starch granules from 18 days post-anthesis (DPA) and on soluble sugar accumulation from 30 DPA. While accumulation of TaAMY1 led to a high degree of damaged starch in grain, the dramatic alterations of starch visco-properties caused by the elevated levels of α-amylase essentially occurred during processing, thus suggesting a very small impact of related starch damage on grain properties. Abnormal accumulation of soluble sugar (α-gluco-oligosaccharide and sucrose) by TaAMY1 over-expression reduced the grain dormancy and enhanced abscisic acid (ABA) resistance. Germination study in the presence of α-amylase inhibitor suggested a very limited role of TaAMY1 in the early germination process and starch conversion into soluble sugars.

Lecithin Inclusion by α-Cyclodextrin Activates SREBP2 Signaling in the Gut and Ameliorates Postprandial Hyperglycemia

BACKGROUND

α-cyclodextrin (α-CD) is one of the dietary fibers that may have a beneficial effect on cholesterol and/or glucose metabolism, but its efficacy and mode of action remain unclear.

METHODS

In the present study, we examined the anti-hyperglycemic effect of α-CD after oral loading of glucose and liquid meal in mice.

RESULTS

Administration of 2 g/kg α-CD suppressed hyperglycemia after glucose loading, which was associated with increased glucagon-like peptide 1 (GLP-1) secretion and enhanced hepatic glucose sequestration. By contrast, 1 g/kg α-CD similarly suppressed hyperglycemia, but without increasing secretions of GLP-1 and insulin. Furthermore, oral α-CD administration disrupts lipid micelle formation through its inclusion of lecithin in the gut luminal fluid. Importantly, prior inclusion of α-CD with lecithin in vitro nullified the anti-hyperglycemic effect of α-CD in vivo, which was associated with increased intestinal mRNA expressions of SREBP2-target genes (Ldlr, Hmgcr, Pcsk9, and Srebp2).

CONCLUSIONS

α-CD elicits its anti-hyperglycemic effect after glucose loading by inducing lecithin inclusion in the gut lumen and activating SREBP2, which is known to induce cholecystokinin secretion to suppress hepatic glucose production via a gut/brain/liver axis.

Overexpression of a wheat α-amylase type 2 impact on starch metabolism and abscisic acid sensitivity during grain germination

Despite being of vital importance for seed establishment and grain quality, starch degradation remains poorly understood in organs such as cereal or legume seeds. In cereals, starch degradation requires the synergetic action of different isoforms of α-amylases. Ubiquitous overexpression of TaAmy2 resulted in a 2.0-437.6-fold increase of total α-amylase activity in developing leaf and harvested grains. These increases led to dramatic alterations of starch visco-properties and augmentation of soluble carbohydrate levels (mainly sucrose and α-gluco-oligosaccharide) in grain. Interestingly, the overexpression of TaAMY2 led to an absence of dormancy in ripened grain due to abscisic acid (ABA) insensitivity. Using an allosteric α-amylase inhibitor (acarbose), we demonstrated that ABA insensitivity was due to the increased soluble carbohydrate generated by the α-amylase excess. Independent from the TaAMY2 overexpression, inhibition of α-amylase during germination led to the accumulation of soluble α-gluco-oligosaccharides without affecting the first stage of germination. These findings support the hypotheses that (i) endosperm sugar may overcome ABA signalling and promote sprouting, and (ii) α-amylase may not be required for the initial stage of grain germination, an observation that questions the function of the amylolytic enzyme in the starch degradation process during germination.

Brewing with Starchy Adjuncts: Its Influence on the Sensory and Nutritional Properties of Beer

In brewing, the use of cereals (wheat, barley, maize, rice, sorghum, oats, rye or millet), pseudo-cereals (buckwheat, quinoa or amaranth) and tubers (sweet potato), as starch adjuncts, is being promoted for the production of a variety of high-quality beers, from sensory and nutritional points of view. The sensory properties of the obtained beer depend on the characteristics of each adjunct but also on the forms in which the adjunct is added: whole cereal, grits, malted, extruded grains, torrefied and syrup. Among these common forms, the extruded grains (maize or rice) produce a higher content of aroma compounds in beer. From a nutritional point of view, the use of non-conventional starch adjuncts, such as black rice, buckwheat or sweet potato, leads to an increase in the polyphenol content of the beer, and thus, its antioxidant capacity. Cereals such as maize, rice, sorghum or millet are the most promising for the production of gluten-free beers. A close relationship can be developed between the use of adjuncts in the beer industry and the use of commercial enzymes. Advances made by biotechnology to design new enzymes with different functionalities could be associated to a future increase in adjunct usage in brewing.

Grain Dimension, Nutrition and Nutraceutical Properties of Black and Red Varieties of Rice in India

Traditional colored rice varieties in India are the source of carbohydrates, phytochemicals and minerals. They facilitate the growth of probiotics in intestine and protect human from many chronic diseases. The present study investigated the nutritional properties such as total sugars, digestible sugars, resistant sugars, hydrolysis index, glycemic index and total proteins of thirteen colored varieties of rice in India. Nutraceutical properties like anti diabetic and prebiotic activity were investigated by standard methods. Chak hao poreiton and mappillai samba grains were 6.3 mm in length. Lowest length of 5.1 mm was recorded in 60 m Kuruvai. Among the rice varieties, mappillai samba has high concentration of digestible starch of 91% and Chak hao poreiton had low concentration of 62%. Resistant starch was 38% in Chak hao poreiton and 8% in mappillai samba. Lowest glycemic index of 52 and 53 were recorded in karuthakar poha and Chak hao poreiton respectively. Anthocyanin extracted from Chak hao poreiton inhibited 24% of human pancreatic α-amylase activity. It significantly increased the probiotic number from 0.15 CFU/mL to 1.95 CFU/mL. The study revealed that the black rice variety, Chak hao poreiton was rich in resistant starch and exhibited low glycemic index. The anthocyanins from Chak hao poreiton possessed significant antidiabetic and prebiotic activity. Molecular docking studies revealed the interaction of anthocyanin with pancreatic α-amylase, β-glucosidase and GLUT1.

Structural Dependence of Sulfated Polysaccharide for Diabetes Management: Fucoidan From Undaria pinnatifida Inhibiting α-Glucosidase More Strongly Than α-Amylase and Amyloglucosidase

Fucoidan refers to a group of sulfated polysaccharide that is commonly obtained from various species of brown seaweed. Fucoidan has gained increased popularity among researchers in the recent years due to its numerous biological activities, including its inhibitory effects against starch hydrolyzing enzymes such as α-amylase and α-glucosidase. This highlights the potential of fucoidan as an antidiabetic agent in the management and prevention of diabetes mellitus. In this study, the inhibitory effects of fucoidan isolated from the New Zealand Undaria pinnatifida seaweed species against three starch hydrolyzing enzymes—α-amylase, α-glucosidase, and amyloglucosidase—was investigated. It was demonstrated that while the fucoidan exhibited significant inhibitory effects against all the three starch hydrolases, it is an uncompetitive inhibitor of α-amylase and amyloglucosidase, and is a competitive inhibitor of α-glucosidase. Moreover, it exhibited significantly stronger inhibitory effects against α-glucosidase than α-amylase, thus having the desirable characteristics as an antidiabetic agent.

Alpha-Cyclodextrin Attenuates the Glycemic and Insulinemic Impact of White Bread in Healthy Male Volunteers

The demonstration of a physiological benefit has recently become an indispensible element of the definition of dietary fibers. In the here-reported pilot study, the effect of alpha-cyclodextrin (alpha-CD) on the postprandial glycemic and insulinemic effect of starch was examined. Twelve fasted, healthy male volunteers received, on three subsequent days, a test breakfast consisting of (A) 100 g fresh white bread (providing 50 g starch) and 250 mL drinking water, (B) the same bread with a supplement of 10 g alpha-CD dissolved in the drinking water, and (C) 25 g alpha-CD dissolved in drinking water. Capillary and venous blood was sampled before the breakfast and in regular intervals for a three-hour period thereafter. Glucose was determined in capillary blood and insulin in the plasma of venous blood samples. Breakfast (A) led to a rapid rise in blood glucose and insulin. In breakfast (B), alpha-CD reduced the areas under the curve of blood glucose and insulin significantly by 59% and 57%, respectively, demonstrating that alpha-CD inhibits and thereby delays starch digestion. Treatment (C) was not associated with a rise of blood glucose. Hence, alpha-CD complies with the current definition of dietary fiber in every respect.

Purification, biochemical, and molecular characterization of a novel extracellular thermostable and alkaline α-amylase from Tepidimonas fonticaldi strain HB23

The present study investigated the purification, biochemical, and molecular characterization of a novel thermostable α-amylase (TfAmy48) from Tepidimonas fonticaldi strain HB23. MALDI-TOF/MS analysis indicated that the purified enzyme is a monomer with a molecular mass of 48,138.10 Da. The results from amino-acid sequence analysis revealed high homology between the 25 NH₂-terminal residues of TfAmy48 and those of Gammaproteobacteria α-amylases. The optimum pH and temperature values for α-amylase activity were pH 8 and 80 °C, respectively. Thin-layer chromatography (TLC) analysis showed that the final hydrolyzed products of the enzyme from soluble potato starch were maltopentaose, maltose, and maltotriose, which indicate that TfAmy48 possessed an endo-acting pattern. Compared to Termamyl®300 L, TfAmy48 showed extreme stability and tolerance towards organic solvents and excellent compatibility with some commercial laundry detergents. These proprieties make TfAmy48 enzyme a potential candidate as a cleaning bioadditive in detergent composition. The Tfamy48 gene encoding TfAmy48 was cloned, sequenced, and heterologously-expressed in the extracellular fraction of Escherichia coli strain BL21(DE3)pLysS. The biochemical properties of the extracellular purified recombinant enzyme (rTfAmy48) were similar to those of native one. The highest sequence identity value (97%) was obtained with PsAmy1 α-amylase from Pseudomonas sp. strain KFCC10818, with only 16 amino-acid (aa) residues of difference.

Characterization of α-Glucosidase Inhibitor/Cyclodextrin Complex Prepared by Freeze-Drying

Miglitol (MT) is an α-glucosidase inhibitor with a postmeal blood glucose level lowering effect that is used to treat type 2 diabetes. In addition, α-cyclodextrin (αCD) has been reported to inhibit increases in postmeal blood glucose. The aim of this study was to prepare a freeze-dried product (FD) composed of MT and αCD or γCD (molar ratio of MT/αCD = 1/1, MT/γCD = 1/1) and to evaluate the physicochemical properties and biological activity of the FD. The PXRD profile of FD exhibited a halo pattern, and characteristic peaks derived from MT, αCD, and γCD were not observed. The TG-DTA results for FD indicated an increased weight loss temperature and the absence of an endothermic peak for MT. The NIR absorption spectrum measurement suggested an intermolecular interaction between MT and αCD or γCD in the FD. ¹H-¹H NOESY NMR spectroscopy (D₂O) revealed an intermolecular interaction in the FD. The results of the α-glucosidase activity inhibition test and the α-amylase activity inhibition test indicated that the FD exhibited the same inhibition rate as MT alone and the effects of MT were not altered by the freeze-drying method.

Extraction and identification of α-amylase inhibitor peptides from Nephelium lappacheum and Nephelium mutabile seed protein using gastro-digestive enzymes

The potential of N. lappacheum and N. mutabile seed as a source of α-amylase inhibitor peptides was explored based on the local traditional practice of using the seed. Different gastro-digestive enzymes (i.e. pepsin or chymotrypsin) or a sequential digestion were used to extract the peptides. The effects of digestion time and enzyme to substrate (E:S) ratio on the α-amylase inhibitory activity were investigated. Results showed that chymotrypsin was effective in producing the inhibitor peptides from rambutan seed protein at E:S ratio 1:20 for 1 h, whereas pepsin was more effective for pulasan seed protein under the same condition. A total of 20 and 31 novel inhibitor peptides were identified, respectively. These peptides could bind with the subsites of α-amylase (i.e. Trp58, Trp59, Tyr62, Asp96, Arg195, Asp197, Glu233, His299, Asp300, and His305) and formed a sliding barrier that preventing the formation of enzyme/substrate intermediate leading to lower α-amylase activity.

Cell wall degradation is required for normal starch mobilisation in barley endosperm

Starch degradation in barley endosperm provides carbon for early seedling growth, but the control of this process is poorly understood. We investigated whether endosperm cell wall degradation is an important determinant of the rate of starch degradation. We identified iminosugar inhibitors of enzymes that degrade the cell wall component arabinoxylan. The iminosugar 1,4-dideoxy-1, 4-imino-l-arabinitol (LAB) inhibits arabinoxylan arabinofuranohydrolase (AXAH) but does not inhibit the main starch-degrading enzymes α- and β-amylase and limit dextrinase. AXAH activity in the endosperm appears soon after the onset of germination and resides in dimers putatively containing two isoforms, AXAH1 and AXAH2. Upon grain imbibition, mobilisation of arabinoxylan and starch spreads across the endosperm from the aleurone towards the crease. The front of arabinoxylan degradation precedes that of starch degradation. Incubation of grains with LAB decreases the rate of loss of both arabinoxylan and starch, and retards the spread of both degradation processes across the endosperm. We propose that starch degradation in the endosperm is dependent on cell wall degradation, which permeabilises the walls and thus permits rapid diffusion of amylolytic enzymes. AXAH may be of particular importance in this respect. These results provide new insights into the mobilization of endosperm reserves to support early seedling growth.

Characterization of thermostable β-amylase isozymes from Lactobacillus fermentum

A strain of Lactobacillus fermentum producing two isozymes of a 20kDa β-amylase was isolated from the faecal sample of a newborn. The starin was identified by sequencing its 16S rRNA gene. The two β-amylase isozymes were resolved and visualized by two dimensional protein gel electrophoresis (2-D gel electrophoresis). Some of the physical and biochemical properties of the enzymes were characterized. The β-amylase displayed two optimum pH s, 5.0 and 10.0 and two optimum temperatures, 45°C and 37°C, respectively. The isozymes hydrolyzed different substrates: glycogen at pH 5.0, and corn starch at pH 10.0. The activity did not require Ca²⁺, though the activity at pH 10.0 was enhanced in the presence of 5.0mM and 10.0mM CaCl_2, 110% and 130%, respectively.

Inhibitory effects of neochamaejasmin B on P-glycoprotein in MDCK-hMDR1 cells and molecular docking of NCB binding in P-glycoprotein

Stellera chamaejasme L. (Thymelaeaceae) is widely distributed in Mongolia, Tibet and the northern parts of China. Its roots are commonly used as “Langdu”, which is embodied in the Pharmacopoeia of the P.R. China (2010) as a toxic Traditional Chinese Medicine. It is claimed to have antivirus, antitumor and antibacterial properties in China and other Asian countries. Studies were carried out to characterize the inhibition of neochamaejasmin B (NCB) on P-glycoprotein (P-gp, ABCB1, MDR1). Rhodamine-123 (R-123) transport and accumulation studies were performed in MDCK-hMDR1 cells. ABCB1 (MDR1) mRNA gene expression and P-gp protein expression were analyzed. Binding selectivity studies based on molecular docking were explored. R-123 transport and accumulation studies in MDCK-hMDR1 cells indicated that NCB inhibited the P-gp-mediated efflux in a concentration-dependent manner. RT-PCR and Western blot demonstrated that the P-gp expression was suppressed by NCB. To investigate the inhibition type of NCB on P-gp, K_i and K_i’ values were determined by double-reciprocal plots in R-123 accumulation studies. Since K_i was greater than K_i’, the inhibition of NCB on P-gp was likely a mixed type of competitive and non-competitive inhibition. The results were confirmed by molecular docking in our current work. The docking data indicated that NCB had higher affinity to P-gp than to Lig1 ((S)-5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-one).

Sequence and structural investigation of a novel psychrophilic α-amylase from Glaciozyma antarctica PI12 for cold-adaptation analysis

A novel α-amylase was isolated successfully from Glaciozyma antarctica PI12 using DNA walking and reverse transcription-polymerase chain reaction (RT-PCR) methods. The structure of this psychrophilic α-amylase (AmyPI12) from G. antarctica PI12 has yet to be studied in detail. A 3D model of AmyPI12 was built using a homology modelling approach to search for a suitable template and to generate an optimum target-template alignment, followed by model building using MODELLER9.9. Analysis of the AmyPI12 model revealed the presence of binding sites for a conserved calcium ion (CaI), non-conserved calcium ions (CaII and CaIII) and a sodium ion (Na). Compared with its template-the thermostable α-amylase from Bacillus stearothermophilus (BSTA)-the binding of CaII, CaIII and Na ions in AmyPI12 was observed to be looser, which suggests that the low stability of AmyPI12 allows the protein to work at different temperature scales. The AmyPI12 amino acid sequence and model were compared with thermophilic α-amylases from Bacillus species that provided the highest structural similarities with AmyPI12. These comparative studies will enable identification of possible determinants of cold adaptation.

Altered large-ring cyclodextrin product profile due to a mutation at Tyr-172 in the amylomaltase of Corynebacterium glutamicum

Corynebacterium glutamicum amylomaltase (CgAM) catalyzes the formation of large-ring cyclodextrins (LR-CDs) with a degree of polymerization of 19 and higher. The cloned CgAM gene was ligated into the pET-17b vector and used to transform Escherichia coli BL21(DE3). Site-directed mutagenesis of Tyr-172 in CgAM to alanine (Y172A) was performed to determine its role in the control of LR-CD production. Both the recombinant wild-type (WT) and Y172A enzymes were purified to apparent homogeneity and characterized. The Y172A enzyme exhibited lower disproportionation, cyclization, and hydrolysis activities than the WT. The k(cat)/K(m) of the disproportionation reaction of the Y172A enzyme was 2.8-fold lower than that of the WT enzyme. The LR-CD product profile from enzyme catalysis depended on the incubation time and the enzyme concentration. Interestingly, the Y172A enzyme showed a product pattern different from that of the WT CgAM at a long incubation time. The principal LR-CD products of the Y172A mutated enzyme were a cycloamylose mixture with a degree of polymerization of 28 or 29 (CD28 or CD29), while the principal LR-CD product of the WT enzyme was CD25 at 0.05 U of amylomaltase. These results suggest that Tyr-172 plays an important role in determining the LR-CD product profile of this novel CgAM.

The role of alpha-glucosidase in germinating barley grains

The importance of α-glucosidase in the endosperm starch metabolism of barley (Hordeum vulgare) seedlings is poorly understood. The enzyme converts maltose to glucose (Glc), but in vitro studies indicate that it can also attack starch granules. To discover its role in vivo, we took complementary chemical-genetic and reverse-genetic approaches. We identified iminosugar inhibitors of a recombinant form of an α-glucosidase previously discovered in barley endosperm (ALPHA-GLUCOSIDASE97 [HvAGL97]), and applied four of them to germinating grains. All four decreased the Glc-to-maltose ratio in the endosperm 10 d after imbibition, implying inhibition of maltase activity. Three of the four inhibitors also reduced starch degradation and seedling growth, but the fourth did not affect these parameters. Inhibition of starch degradation was apparently not due to inhibition of amylases. Inhibition of seedling growth was primarily a direct effect of the inhibitors on roots and coleoptiles rather than an indirect effect of the inhibition of endosperm metabolism. It may reflect inhibition of glycoprotein-processing glucosidases in these organs. In transgenic seedlings carrying an RNA interference silencing cassette for HvAgl97, α-glucosidase activity was reduced by up to 50%. There was a large decrease in the Glc-to-maltose ratio in these lines but no effect on starch degradation or seedling growth. Our results suggest that the α-glucosidase HvAGL97 is the major endosperm enzyme catalyzing the conversion of maltose to Glc but is not required for starch degradation. However, the effects of three glucosidase inhibitors on starch degradation in the endosperm indicate the existence of unidentified glucosidase(s) required for this process.

Modified alpha-amylase activity among insecticide-resistant and -susceptible strains of the maize weevil, Sitophilus zeamais

Fitness cost is usually associated with insecticide resistance and may be mitigated by increased energy accumulation and mobilization. Preliminary evidence in the maize weevil (Coleoptera: Curculionidae) suggested possible involvement of amylases in such phenomenon. Therefore, alpha-amylases were purified from an insecticide-susceptible and two insecticide-resistant strains (one with fitness cost [resistant cost strain], and the other without it [resistant no-cost strain]). The main alpha-amylase of each strain was purified by glycogen precipitation and ion-exchange chromatography (>or=70-fold purification, <or=19% yield). Single alpha-amylase bands with the same molecular mass (53.7kDa) were revealed for each insect strain. Higher activity was obtained at 35-40 degrees C and at pH 5.0-7.0 for all of the strains. The alpha-amylase from the resistant no-cost strain exhibited higher activity towards starch and lower inhibition by acarbose and wheat amylase inhibitors. Opposite results were observed for the alpha-amylase from the resistant cost strain. Although the alpha-amylase from the resistant cost strain exhibited higher affinity to starch (i.e., lower K(m)), its V(max)-value was the lowest among the strains, particularly the resistant no-cost strain. Such results provide support for the hypothesis that enhanced alpha-amylase activity may be playing a major role in mitigating fitness costs associated with insecticide resistance.

A large-scale survey of genetic copy number variations among Han Chinese residing in Taiwan

BACKGROUND

Copy number variations (CNVs) have recently been recognized as important structural variations in the human genome. CNVs can affect gene expression and thus may contribute to phenotypic differences. The copy number inferring tool (CNIT) is an effective hidden Markov model-based algorithm for estimating allele-specific copy number and predicting chromosomal alterations from single nucleotide polymorphism microarrays. The CNIT algorithm, which was constructed using data from 270 HapMap multi-ethnic individuals, was applied to identify CNVs from 300 unrelated Han Chinese individuals in Taiwan.

RESULTS

Using stringent selection criteria, 230 regions with variable copy numbers were identified in the Han Chinese population; 133 (57.83%) had been reported previously, 64 displayed greater than 1% CNV allele frequency. The average size of the CNV regions was 322 kb (ranging from 1.48 kb to 5.68 Mb) and covered a total of 2.47% of the human genome. A total of 196 of the CNV regions were simple deletions and 27 were simple amplifications. There were 449 genes and 5 microRNAs within these CNV regions; some of these genes are known to be associated with diseases.

CONCLUSION

The identified CNVs are characteristic of the Han Chinese population and should be considered when genetic studies are conducted. The CNV distribution in the human genome is still poorly characterized, and there is much diversity among different ethnic populations.

New thermostable amylase from Bacillus cohnii US147 with a broad pH applicability

A new thermophilic bacterial strain identified as Bacillus cohnii US147 was isolated from the southern Tunisian soil. The identification was based on physiological tests and molecular techniques related to the 16S ribosomal ribonucleic acid. The isolated strain produced amylase, which was purified. This amylase had an apparent molecular mass of 30 kDa as estimated by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Amylase US147 showed K (m) and V (max) values of 0.7 mg/ml and 2.2 U/ml, respectively, with starch as the substrate. The enzyme was active in acid and basic pH and had a maximal activity on starch at pH 9 and 70 degrees C. The enzyme was stable at pH 9 for 72 h and retained half of its activity after incubation at 70 degrees C for 150 min. A partially inhibition (15%, 25%, 23%, 20%, and 22%) was obtained with 1 mM SDS, 1 mM NaBO(3), 1 mM H(2)O(2,) 1 mM Zn(+2), and 5 mM ethylenediamine tetraacetic acid (EDTA), respectively. The amylase recovered its original activity by the addition of 10 mM Ca (2+) to the 5 mM EDTA. These properties indicated a possible use of this amylase in starch saccharification, in detergent, and in other industrial applications.

The 'pair of sugar tongs' site on the non-catalytic domain C of barley alpha-amylase participates in substrate binding and activity

Some starch-degrading enzymes accommodate carbohydrates at sites situated at a certain distance from the active site. In the crystal structure of barley alpha-amylase 1, oligosaccharide is thus bound to the 'sugar tongs' site. This site on the non-catalytic domain C in the C-terminal part of the molecule contains a key residue, Tyr380, which has numerous contacts with the oligosaccharide. The mutant enzymes Y380A and Y380M failed to bind to beta-cyclodextrin-Sepharose, a starch-mimic resin used for alpha-amylase affinity purification. The K(d) for beta-cyclodextrin binding to Y380A and Y380M was 1.4 mm compared to 0.20-0.25 mm for the wild-type, S378P and S378T enzymes. The substitution in the S378P enzyme mimics Pro376 in the barley alpha-amylase 2 isozyme, which in spite of its conserved Tyr378 did not bind oligosaccharide at the 'sugar tongs' in the structure. Crystal structures of both wild-type and S378P enzymes, but not the Y380A enzyme, showed binding of the pseudotetrasaccharide acarbose at the 'sugar tongs' site. The 'sugar tongs' site also contributed importantly to the adsorption to starch granules, as Kd = 0.47 mg.mL(-1) for the wild-type enzyme increased to 5.9 mg.mL(-1) for Y380A, which moreover catalyzed the release of soluble oligosaccharides from starch granules with only 10% of the wild-type activity. beta-cyclodextrin both inhibited binding to and suppressed activity on starch granules for wild-type and S378P enzymes, but did not affect these properties of Y380A, reflecting the functional role of Tyr380. In addition, the Y380A enzyme hydrolyzed amylose with reduced multiple attack, emphasizing that the 'sugar tongs' participates in multivalent binding of polysaccharide substrates.

Identification of Acceptor Substrate Binding Subsites +2 and +3 in the Amylomaltase from Thermus thermophilus HB8

Glycoside hydrolase family 77 (GH77) belongs to the alpha-amylase superfamily (Clan H) together with GH13 and GH70. GH77 enzymes are amylomaltases or 4-alpha-glucanotransferases, involved in maltose metabolism in microorganisms and in starch biosynthesis in plants. Here we characterized the amylomaltase from the hyperthermophilic bacterium Thermus thermophilus HB8 (Tt AMase). Site-directed mutagenesis of the active site residues (Asp293, nucleophile; Glu340, general acid/base catalyst; Asp395, transition state stabilizer) shows that GH77 Tt AMase and GH13 enzymes share the same catalytic machinery. Quantification of the enzyme's transglycosylation and hydrolytic activities revealed that Tt AMase is among the most efficient 4-alpha-glucanotransferases in the alpha-amylase superfamily. The active site contains at least seven substrate binding sites, subsites -2 and +3 favoring substrate binding and subsites -3 and +2 not, in contrast to several GH13 enzymes in which subsite +2 contributes to oligosaccharide binding. A model of a maltoheptaose (G7) substrate bound to the enzyme was used to probe the details of the interactions of the substrate with the protein at acceptor subsites +2 and +3 by site-directed mutagenesis. Substitution of the fully conserved Asp249 with a Ser in subsite +2 reduced the activity 23-fold (for G7 as a substrate) to 385-fold (for maltotriose). Similar mutations reduced the activity of alpha-amylases only up to 10-fold. Thus, the characteristics of acceptor subsite +2 represent a main difference between GH13 amylases and GH77 amylomaltases.

Proteomic of lipid rafts in the exocrine pancreas from diet-induced obese rats

In the present work, we induced obesity in rats with high-energy-starch diet and studied exocrine pancreas response. The zymogen granule (ZG) or purified plasma membrane (PM) from the exocrine pancreas was used for the isolation of the detergent-resistant membranes (DRMs). Based on high content of cholesterol, GM1, the bile salt dependent lipase (BSDL), and GP2 enrichment, the low-density fractions were defined as lipid rafts. Additionally, the rafts vesicles were determined by immunogold labeling with anti BSDL. By combining MALDI-TOF/MS and nano-LC ESI Q-TOF MS/MS proteomic identification we have selected 33 proteins from the lipid rafts which were classified into at least four functional families. Our data suggest that the acinar PM from the diet-induced obesity rats may be organized into lipid rafts, and characterization of rafts proteome can contribute to improve our understanding of food digestion under obesity.

A highly thermostable and alkaline amylase from a Bacillus sp. PN5

A highly thermostable alkaline amylase producing Bacillus sp. PN5 was isolated from soil, which yielded 65.23 U mL(-1) of amylase in medium containing (%) 0.6 starch, 0.5 peptone and 0.3 yeast extract at 60 degrees C, pH 7.0 after 60 h of incubation. Maximum amylase activity was at pH 10.0 and 90 degrees C. The enzyme retained 80% activity after 1 h at pH 10.0. It exhibited 65% activity at 105 degrees C and had 100% stability in the temperature range between 80 and 100 degrees C for 1 h. In addition, there was 86.36% stability after 1-h incubation with sodium dodecylsulphate. These properties indicated possible use of this amylase in starch saccharification and detergent formulation.

The mechanism of action of alpha-amylase from Lactobacillus fermentum on maltooligosaccharides

The action pattern of Lactobacillus fermentum alpha-amylase (FERMENTA) was examined using a series of maltooligosaccharides (G2-G7) as substrates. Structurally, this enzyme has a molecular mass (106 kDa) almost twofold higher than alpha-amylases from mammalians and cereals. The product pattern was investigated through an analysis of products and substrates using HPAEC with pulsed amperometric detection. FERMENTA was consistent with an endo-type of amylase. The bond cleavage frequencies were studied using maltooligosaccharides of various chain lengths as substrate, i.e. maltose up to maltoheptaose and DP 4900-amylose catalyzed by FERMENTA. The catalytic efficiency (k(cat)/K(m)) increased with chain length from maltose (8.7 x 10(4) M(-1) s(-1)) up to amylose (1 x10(9) M(-1) s(-1)). These action pattern results revealed that FERMENTA can readily cleave the third linkage from the reducing end of the maltooligosaccharides (G5-G7).

Amylomaltase of Pyrobaculum aerophilum IM2 produces thermoreversible starch gels

Amylomaltases are 4-alpha-glucanotransferases (EC 2.4.1.25) of glycoside hydrolase family 77 that transfer alpha-1,4-linked glucans to another acceptor, which can be the 4-OH group of an alpha-1,4-linked glucan or glucose. The amylomaltase-encoding gene (PAE1209) from the hyperthermophilic archaeon Pyrobaculum aerophilum IM2 was cloned and expressed in Escherichia coli, and the gene product (PyAMase) was characterized. PyAMase displays optimal activity at pH 6.7 and 95 degrees C and is the most thermostable amylomaltase described to date. The thermostability of PyAMase was reduced in the presence of 2 mM dithiothreitol, which agreed with the identification of two possible cysteine disulfide bridges in a three-dimensional model of PyAMase. The kinetics for the disproportionation of malto-oligosaccharides, inhibition by acarbose, and binding mode of the substrates in the active site were determined. Acting on gelatinized food-grade potato starch, PyAMase produced a thermoreversible starch product with gelatin-like properties. This thermoreversible gel has potential applications in the food industry. This is the first report on an archaeal amylomaltase.