Characterization and functional properties of the alpha-amylase inhibitor (alpha-AI) from kidney bean (Phaseolus vulgaris) seeds

Large-scale computational screening of Indian medicinal plants reveals Cassia angustifolia to be a potentially anti-diabetic

Researchers are investigating the medicinal properties of herbal plants throughout the world, which often leads to the discovery of novel plants and their chemicals for prophylactic needs of humans. Natural phytochemicals continue to be sought as alternative treatments for various diseases because of their non-toxic and therapeutic properties. In recent years, computational phytochemistry has enabled large-scale screening of phytochemicals, enabling researchers to pursue a wide range of therapeutic research alternatives to traditional ethnopharmacology. We propose to identify an anti-diabetic plant by computational screening on Indian herbal plants in conjunction with experimental characterization and biological validation. The methodology involves the creation of an in-house Indian herbal plant database. Molecular docking is used to screen against alpha amylase for anti-diabetic prophylaxis. Cassia angustifolia was chosen because its phytochemicals are able to bind to alpha amylase. Plants were experimentally extracted, botanically studied and their biological activity was evaluated. Further, the use of molecular dynamics was then applied to pinpoint the phytochemicals responsible for the affinity of alpha amylase. Results in the phytochemical analysis of the extracts revealed strong presence of alkaloids, flavonoids and cardiac glycosides. Moreover, alpha amylase biological activity with C. angustifolia extracts of chloroform, hexane and ethyl acetate demonstrated activity of 3.26, 8.01 and 30.33 µg/ml validating computational predictions. In conclusion, this study developed, validated computational predictions of identifying potential anti-diabetic plants 'Cassia angustifolia' from house herbal databases. Hope this study shall inspire explore plant therapeutic repurposing using computational methods of drug discovery.Communicated by Ramaswamy H. Sarma.

Biochemical and Phylogenetic Analysis of Italian Phaseolus vulgaris Cultivars as Sources of α-Amylase and α-Glucosidase Inhibitors

Phaseolus vulgaris α-amylase inhibitor (α-AI) is a protein that has recently gained commercial interest, as it inhibits mammalian α-amylase activity, reducing the absorption of dietary carbohydrates. Numerous studies have reported the efficacy of preparations based on this protein on the control of glycaemic peaks in type-2 diabetes patients and in overweight subjects. A positive influence on microbiota regulation has also been described. In this work, ten insufficiently studied Italian P. vulgaris cultivars were screened for α-amylase- and α-glucosidase-inhibiting activity, as well as for the absence of antinutritional compounds, such as phytohemagglutinin (PHA). All the cultivars presented α-glucosidase-inhibitor activity, while α-AI was missing in two of them. Only the Nieddone cultivar (ACC177) had no haemagglutination activity. In addition, the partial nucleotide sequence of the α-AI gene was identified with the degenerate hybrid oligonucleotide primer (CODEHOP) strategy to identify genetic variability, possibly linked to functional α-AI differences, expression of the α-AI gene, and phylogenetic relationships. Molecular studies showed that α-AI was expressed in all the cultivars, and a close similarity between the Pisu Grogu and Fasolu cultivars' α-AI and α-AI-4 isoform emerged from the comparison of the partially reconstructed primary structures. Moreover, mechanistic models revealed the interaction network that connects α-AI with the α-amylase enzyme characterized by two interaction hotspots (Asp38 and Tyr186), providing some insights for the analysis of the α-AI primary structure from the different cultivars, particularly regarding the structure-activity relationship. This study can broaden the knowledge about this class of proteins, fuelling the valorisation of Italian agronomic biodiversity through the development of commercial preparations from legume cultivars.

Phenolic profile, alpha-amylase inhibitory activity, and in vitro glycemic index of adzuki beans

Regular consumption of low-glycemic index (GI) foods is a common strategy for type 2 diabetes patients. To evaluate the potential application of adzuki beans in low-GI foods, the phenolic profile and alpha-amylase inhibitor (α-AI) activity of four varieties of adzuki beans (G24, Te Xiao Li No. 1, Gui Nong No. 1, and Qian Xiao Hei) were determined. The starch digestibility properties and in vitro glycemic index (IVGI) of these beans were also evaluated using the in vitro digestion model coupled with 3,5-dinitrosalicylic acid colorimetry. The results indicated that these adzuki beans, containing numerous phenolics, showed inhibitory activities to alpha-amylase with the α-AI activities between 1.760 ± 0.044 and 3.411 ± 0.186 U/g. The resistant starch (RS) contributed predominantly to the total starch with proportions between (69.78 ± 2.45%) and (81.03 ± 0.06%); Te Xiao Li No. 1 was the highest compared with the other varieties. The adzuki beans were categorized into low- or medium-GI foods, and the IVGI ranged from (39.00 ± 0.36) to (56.76 ± 4.21). These results suggested that adzuki beans can be used as a component of low-GI foods.

Comparison of Glycemic Response to Carbohydrate Meals without or with a Plant-Based Formula of Kidney Bean Extract, White Mulberry Leaf Extract, and Green Coffee Extract in Individuals with Abdominal Obesity

Due to the rising prevalence of obesity and type 2 diabetes, a strategy that can positively influence diet quality in a simple way is being explored, since a low glycemic index (GI) diet is advised in the dietoprophylaxis and diet therapy of diabetes. Methods: Twenty-three women with abdominal obesity participated in the study. The postprandial glycemic response and glycemic index were determined after three carbohydrate meals (noodle soup, white rice, strawberry sorbet) without or with the addition of a plant-base supplement (extracts of kidney bean, white mulberry leaf, and green coffee) with a potentially hypoglycemic effect. For two products (instant noodle soup and white rice), the addition of the plant supplement resulted in a reduction in glicemic iAUC values (respectively, by: 17.1%, p = 0.005 and 5.3%; p = 0.03; 40.6%, p = 0.004 and 5.3%, p = 0.019). However, this effect was not observed for strawberry sorbet. The blood glucose concentrations 30 min after the consumption of instant noodle soup and white rice with the plant-based formula addition significantly affected the GI value of tested meals (p = 0.0086, r = 0.53; p = 0.0096, r = 0.53), which may indicate the effect of this plant supplement on enterohormone and/or insulin secretion. Conclusion: A formula containing kidney bean, white mulberry leaves, and green coffee extracts may therefore be a notable factor in lowering postprandial glycemia and the GI of carbohydrate foods. However, further research is needed to determine for which food groups and meals its use may be most effective.

Common bean (Phaseolus vulgaris L.) α-amylase inhibitors as safe nutraceutical strategy against diabetes and obesity: An update review

Overweight and obesity are constantly increasing, not only in Western countries but also in low‐middle‐income ones. The decrease of both the intake of carbohydrates and their assimilation are among the main dietary strategies to counter these conditions. α‐Amylase, a key enzyme involved in the digestion of carbohydrates, is the target enzyme to reduce the absorption rate of carbohydrates. α‐Amylase inhibitors (α‐AIs) can be found in plants. The common bean, Phaseolus vulgaris is of particular interest due to the presence of protein‐based α‐AIs which, through a protein–protein interaction, reduce the activity of this enzyme. Here we describe the nature of the various types of common bean seed extracts, the type of protein inhibitors they contain, reviewing the recent Literature about their molecular structure and mechanism of action. We also explore the existing evidence (clinical trials conducted on both animals and humans) supporting the potential benefits of this protein inhibitors from P. vulgaris, also highlighting the urgent need of further studies to confirm the clinical efficacy of the commercial products. This work could contribute to summarize the knowledge and application of P. vulgaris extract as a nutraceutical strategy for controlling unwanted weight gains, also highlighting the current limitations.

Molecular determinant for specificity: Differential interaction of α-amylases with their proteinaceous inhibitors

BACKGROUND

α-Amylase inhibitors (α-AIs) belong to the discrete classes, and exhibited differential specificities against α-amylases from various sources. Several α-amylases and their complexes with inhibitors at the molecular level have been studied in detail. Interestingly, some α-AIs depict specific and selective interactions amid different insect α-amylases.

SCOPE OF REVIEW

There are studies to understand evolutionary variability and functional differentiation of insect α-amylases and their cognate inhibitors. We have examined sequence, structural, and interaction diversity between various α-amylases and α-AIs. Based on these analyses, we are providing a potential basis for the functional differentiation among certain insect α-amylases concerning mammalian counterparts and their interactions with different proteinaceous α-AIs.

MAJOR CONCLUSIONS

Insect α-amylases have conserved domain architecture with differences in length, number of disulfide bonds, and secondary structure. Furthermore, few of them exhibit variable characteristics like chloride dependent activity, the presence of N-terminal glutamine residue to protect against proteolytic degradation, and loop variations near the enzyme active site. Conformation of α-AI protein could be an essential factor for their specificity and binding affinities towards target α-amylase(s). Furthermore, variation into the enzyme binding pocket residues might contribute to differential interactions with inhibitors.

GENERAL SIGNIFICANCE

Molecular insights in the interactions between insect α-amylases and plant α-AI will provide the details of mechanisms assisting the inhibitor specificity. Furthermore, this information will help to design potent and effective α-AIs against specific α-amylase.

Glutinous rice (Oryza sativa L.) protein extract with potent α-amylase inhibitory activity

This research screened for α-amylase inhibitory activity of twenties-five varieties Thai indigenous rice seeds. Based on specific inhibition, crude protein of var. Gai Ngaw (Gs. No. 13719) was selected for purification. The unbound proteins of the Q-Sepharose column named partially purified rice α-amylase inhibitor (RAI) revealed MW of approximately 14.4 kDa. The RAI was stable at pH 4 to 7 and heat stable up to 80 °C. The RAI had IC₅₀ of 15.92 ± 1.08 µg/ml. The double reciprocal plot implied a mixed-type inhibitor. The Dixon and Cornish-Bowden plots were used to estimate Ki and αKi. This suggested Thai indigenous rice seeds could potentially be developed as a food supplement for blood sugar and weight controls.

Purification, developmental expression, and in silico characterization of α-amylase inhibitor from Echinochloa frumentacea

Barnyard (Echinochloa frumentacea) and finger (Eleusine coracana) millet growing at northwestern Himalaya were explored for the α-amylase inhibitor (α-AI). The mature seeds of barnyard millet variety PRJ1 had maximum α-AI activity which increases in different developmental stage. α-AI was purified up to 22.25-fold from barnyard millet variety PRJ1. Semi-quantitative PCR of different developmental stages of barnyard millet seeds showed increased levels of the transcript from 7 to 28 days. Sequence analysis revealed that it contained 315 bp nucleotide which encodes 104 amino acid sequence with molecular weight 10.72 kDa. The predicted 3D structure of α-AI was 86.73% similar to a bifunctional inhibitor of ragi. In silico analysis of 71 α-AI protein sequences were carried out for biochemical features, homology search, multiple sequence alignment, phylogenetic tree construction, motif, and superfamily distribution of protein sequences. Analysis of multiple sequence alignment revealed the existence of conserved regions NPLP[S/G]CRWYVV[S/Q][Q/R]TCG[V/I] throughout sequences. Superfam analysis revealed that α-AI protein sequences were distributed among seven different superfamilies.

Systematic Review and Meta-Analysis of a Proprietary Alpha-Amylase Inhibitor from White Bean (Phaseolus vulgaris L.) on Weight and Fat Loss in Humans

The aim of this meta-analysis was to examine the evidence for the effectiveness of a proprietary alpha-amylase inhibitor from white bean (Phaseolus vulgaris L.) supplementation interventions in humans on modification of body weight and fat mass. A systematic literature search was performed using three databases: PubMed, the Cochrane collaboration, and Google Scholar. In addition, the manufacturer was contacted for internal unpublished data, and finally, the reference section of relevant original research and review papers were mined for additional studies. Eleven studies were selected for the meta-analysis of weight loss (a total of 573 subjects), and three studies for the meta-analysis of body fat reduction (a total of 110 subjects), as they fulfilled the inclusion criteria. Phaseolus vulgaris supplementation showed an average effect on weight loss difference of −1.08 kg (95% CI (confidence interval), −0.42 kg to −1.16 kg, p < 0.00001), and the average effect on body fat reduction was 3.26 kg (95% CI, −2.35 kg to −4.163 kg, p = 0.02). This meta-analysis found statistically significant effects of Phaseolus vulgaris supplementation on body weight and body fat.

Heterologous expression of an α-amylase inhibitor from common bean (Phaseolus vulgaris) in Kluyveromyces lactis and Saccharomyces cerevisiae

Background

Phaseolamin or α-amylase inhibitor 1 (αAI) is a glycoprotein from common beans (Phaseolus vulgaris L.) that inhibits some insect and mammalian α-amylases. Several clinical studies support the beneficial use of bean αAI for control of diabetes and obesity. Commercial extracts of P. vulgaris are available but their efficacy is still under question, mainly because some of these extracts contain antinutritional impurities naturally present in bean seeds and also exhibit a lower specific activity αAI. The production of recombinant αAI allows to overcome these disadvantages and provides a platform for the large-scale production of pure and functional αAI protein for biotechnological and pharmaceutical applications.

Results

A synthetic gene encoding αAI from the common bean (Phaseolus vulgaris cv. Pinto) was codon-optimised for expression in yeasts (αAI-OPT) and cloned into the protein expression vectors pKLAC2 and pYES2. The yeasts Kluyveromyces lactis GG799 (and protease deficient derivatives such as YCT390) and Saccharomyces cerevisiae YPH499 were transformed with the optimised genes and transformants were screened for expression by antibody dot blot. Recombinant colonies of K. lactis YCT390 that expressed and secreted functional αAI into the culture supernatants were selected for further analyses. Recombinant αAI from K. lactis YCT390 was purified using anion-exchange and affinity resins leading to the recovery of a functional inhibitor. The identity of the purified αAI was confirmed by mass spectrometry. Recombinant clones of S. cerevisiae YPH499 expressed functional αAI intracellularly, but did not secrete the protein.

Conclusions

This is the first report describing the heterologous expression of the α-amylase inhibitor 1 (αAI) from P. vulgaris in yeasts. We demonstrated that recombinant strains of K. lactis and S. cerevisiae expressed and processed the αAI precursor into mature and active protein and also showed that K. lactis secretes functional αAI.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0719-4) contains supplementary material, which is available to authorized users.

Discovery and characterization of pseudocyclic cystine-knot α-amylase inhibitors with high resistance to heat and proteolytic degradation

Obesity and type 2 diabetes are chronic metabolic diseases, and those affected could benefit from the use of α-amylase inhibitors to manage starch intake. The pseudocyclics, wrightides Wr-AI1 to Wr-AI3, isolated from an Apocynaceae plant show promise for further development as orally active α-amylase inhibitors. These linear peptides retain the stability known for cystine-knot peptides in the presence of harsh treatment. They are resistant to heat treatment and endopeptidase and exopeptidase degradation, which is characteristic of cyclic cystine-knot peptides. Our NMR and crystallography analysis also showed that wrightides, which are currently the smallest proteinaceous α-amylase inhibitors reported, contain the backbone-twisting cis-proline, which is preceded by a nonaromatic residue rather than a conventional aromatic residue. The modeled structure and a molecular dynamics study of Wr-AI1 in complex with yellow mealworm α-amylase suggested that, despite having a similar structure and cystine-knot fold, the knottin-type α-amylase inhibitors may bind to insect α-amylase via a different set of interactions. Finally, we showed that the precursors of pseudocyclic cystine-knot α-amylase inhibitors and their biosynthesis in plants follow a secretory protein synthesis pathway. Together, our findings provide insights for the use of the pseudocyclic α-amylase inhibitors as useful leads for the development of orally active peptidyl bioactives, as well as an alternative scaffold for cyclic peptides for engineering metabolically stable human α-amylase inhibitors.

Twenty Traditional Algerian Plants Used in Diabetes Therapy as Strong Inhibitors of α-Amylase Activity

In the present work, we have studied the inhibitory effects of aqueous and alcoholic extracts of six Algerian medicinal plants known by their therapeutic virtues against diabetes. The total phenolic compounds content, assayed using Folin-Ciocalteu’s reagent, of the samples ranged from 0.183 mg/g to 43.088 mg/g and from 1.197 mg/g to 7.445 mg/g, expressed as gallic acid equivalent (GAE), for the, respectively, whereas the total flavonoids concentrations, detected using 2% of the aluminium chloride, ranged from 0.41 mg/g to 11.613 mg/g and from 0.0097 mg/g to 1.591 mg/g, expressed as rutin equivalents (RE), for the aqueous and methanolic extracts, respectively. The major plants were found to inhibit enzymatic activities of Aspergillus oryzae-amylase in a concentration dependent manner. The values of the inhibition constants (Ki) have been determined according to the Dixon and Lineweaver-Burk methods. The results showed that the Ki values were less than 55 ppm for the all extracts. A strong inhibition was found in the phenolic extract of Salvia officinalis with a Ki of 8 ppm.

An in vitro and in vivo study of the α-amylase activity of phaseolamin

We evaluated the polypeptide profiles, inhibition of human salivary α-amylase activity, and hemagglutination properties of a commercial phaseolamin sample. We also performed an in vivo assay to investigate the effects of a commercial phaseolamin treatment (100, 500, or 1500 mg/kg) over 20 days on the glycemia, body weight, and serum biochemical parameters (total cholesterol, triglycerides, alanine aminotransferase, and aspartate aminotransferase) of nondiabetic and streptozotocin-induced diabetic rats. The in vitro evaluation showed defined protein profiles, low hemagglutination activity, and high α-amylase inhibition. None of the experimental groups treated with phaseolamin or acarbose showed decreases in body weight. Our data demonstrate that phaseolamin inhibits amylase activity in vitro, reduces blood glucose levels, decreases or attenuates some of the renal and hepatic effects of diabetes in streptozotocin-induced rats, and could therefore have therapeutic potential in the treatment or prevention of the complications of diabetes.

Functional characterization of a vacuolar invertase from Solanum lycopersicum: post-translational regulation by N-glycosylation and a proteinaceous inhibitor

Plant vacuolar invertases, which belong to family 32 of glycoside hydrolases (GH32), are key enzymes in sugar metabolism. They hydrolyse sucrose into glucose and fructose. The cDNA encoding a vacuolar invertase from Solanum lycopersicum (TIV-1) was cloned and heterologously expressed in Pichia pastoris. The functional role of four N-glycosylation sites in TIV-1 has been investigated by site-directed mutagenesis. Single mutations to Asp of residues Asn52, Asn119 and Asn184, as well as the triple mutant (Asn52, Asn119 and Asn184), lead to enzymes with reduced specific invertase activity and thermostability. Expression of the N516D mutant, as well as of the quadruple mutant (N52D, N119D, N184D and N516D) could not be detected, indicating that these mutations dramatically affected the folding of the protein. Our data indicate that N-glycosylation is important for TIV-1 activity and that glycosylation of N516 is crucial for recombinant enzyme stability. Using a functional genomics approach a new vacuolar invertase inhibitor of S. lycopersicum (SolyVIF) has been identified. SolyVIF cDNA was cloned and heterologously expressed in Escherichia coli. Specific interactions between SolyVIF and TIV-1 were investigated by an enzymatic approach and surface plasmon resonance (SPR). Finally, qRT-PCR analysis of TIV-1 and SolyVIF transcript levels showed a specific tissue and developmental expression. TIV-1 was mainly expressed in flowers and both genes were expressed in senescent leaves.

α-Amylase inhibitory activity from nut seed skin polyphenols. 1. Purification and characterization of almond seed skin polyphenols

Using α-amylase inhibition as a separation guide, polyphenolic compounds from almond ( Prunus dulcis ) seed skin were purified using ultrafiltration and Sephadex LH-20 and ODS columns. The purified fraction specifically and strongly inhibited α-amylase; the IC50 value was 2.2 μg/mL for pig pancreatic α-amylase. The fraction contained about 62% of the total polyphenols, 33.8% flavanol-type tannins and 30% procyanidins. Oral administration of the polyphenol fraction to rats fed corn starch significantly suppressed an increase in blood glucose levels and area under the curve (AUC), in a dose-dependent manner. High-resolution MALDI-TOF mass spectra showed that the structure of this sample is a series of polyflavan-3-ol polymers composed of catechin/epicatechin units and gallocatechin/epigallocatechin units up to 11-mer with several interflavanoid ether linkages. The results suggest almond seed skin contains highly polymerized polyphenols with strong α-amylase inhibitory activity, which retard absorption of carbohydrate.

Reflection on design and testing of pancreatic alpha-amylase inhibitors: an in silico comparison between rat and rabbit enzyme models

Background

Inhibitors of pancreatic alpha-amylase are potential drugs to treat diabetes and obesity. In order to find compounds that would be effective amylase inhibitors, in vitro and in vivo models are usually used. The accuracy of models is limited, but these tools are nonetheless valuable. In vitro models could be used in large screenings involving thousands of chemicals that are tested to find potential lead compounds. In vivo models are still used as preliminary mean of testing compounds behavior in the whole organism. In the case of alpha-amylase inhibitors, both rats and rabbits could be chosen as in vivo models. The question was which animal could present more accuracy with regard to its pancreatic alpha-amylase.

Results

As there is no crystal structure of these enzymes, a molecular modeling study was done in order to compare the rabbit and rat enzymes with the human one. The overall result is that rabbit enzyme could probably be a better choice in this regard, but in the case of large ligands, which could make putative interactions with the −4 subsite of pancreatic alpha-amylase, interpretation of results should be made cautiously.

Conclusion

Molecular modeling tools could be used to choose the most suitable model enzyme that would help to identify new enzyme inhibitors. In the case of alpha-amylase, three-dimensional structures of animal enzymes show differences with the human one which should be taken into account when testing potential new drugs.

Improved rapid detection of trypsin isoinhibitors using non-denaturing polyacrylamide gels with immobilised azoalbumin

INTRODUCTION

Proteinaceous inhibitors of animal trypsin occur naturally as isoforms in seeds and some are of interest as antinutritional or anti-pest agents.

OBJECTIVE

To establish a simplified electrophorectic, in-gel method for rapid and direct detection of trypsin isoinhibitors present in crude plant extracts that are particularly suitable for many studies including rapid evaluation of cultivars.

METHODOLOGY

Azoalbumin (3%, w/v) is immobilised in 7.5% polyacrylamide gels before electrophoresis under non-denaturing conditions.

RESULTS

This improved method eliminates the need for both time-consuming and labourious staining and destaining or renaturation steps.

CONCLUSION

Immobilised azoalbumin in polyacrylamide gels, run under non-denaturing electrophoresis conditions, can be used to assist rapid evaluation of trypsin isoinhibitors in numerous crude plant extracts.

Biochemical characterization of the alpha-amylase inhibitor in mungbeans and its application in inhibiting the growth of Callosobruchus maculatus

The insect Callosobruchus maculatus causes considerable damage to harvested mungbean seeds every year, which leads to commercial losses. However, recent studies have revealed that mungbean seeds contain alpha-amylase inhibitors that can inhibit the protein C. maculatus, preventing growth and development of the insect larvae in the seed, thus preventing further damage. For this reason, the use of alpha-amylase inhibitors to interfere with the pest's digestion process has become an interesting alternative biocontrolling agent. In this study, we have isolated and purified the alpha-amylase inhibitor from mungbean seeds (KPS1) using ammonium sulfate precipitation, gel filtration chromatography and reversed phase HPLC. We found that the alpha-amylase inhibitor, isolated as a monomer, had a molecular weight of 27 kDa. The alpha-amylase inhibitor was purified 750-fold with a final yield of 0.4 mg of protein per 30 g of mungbean seeds. Its specific activity was determined at 14.5 U (mg of protein)(-1). Interestingly, we found that the isolated alpha-amylase inhibitor inhibits C. maculatus alpha-amylase but not human salivary alpha-amylase. After preincubation of the enzyme with the inhibitor, the mungbean alpha-amylase inhibitor inhibited C. maculatus alpha-amylase activity by decreasing V(max) while increasing the K(m) constant, indicating that the mungbean alpha-amylase is a mix noncompetitive inhibitor. The in vivo effect of alpha-amylase inhibitor on the mortality of C. maculatus shows that the alpha-amylase inhibitor acts on C. maculatus during the development stage, by reducing carbohydrate digestion necessary for growth and development, rather than during the end laying/hatching stage. Our results suggest that mungbean alpha-amylase inhibitor could be a useful future biocontrolling agent.

Inhibition of Sunn pest, Eurygaster integriceps, α-amylases by α-amylase inhibitors (T-αAI) from Triticale

The effect of triticale α-amylases inhibitors on starch hydrolysis catalyzed by the Sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae) midgut amylases was examined. Biochemical studgawies showed that inhibitors from Triticale (a hybrid of wheat and rye) had inhibitiory effects on E. integriceps α-amylases. The effects of the triticale α-amylase inhibitor (T-αAI) on α-amylase of E. integriceps showed a dose dependent manner of inhibition, e.g. less inhibition of enzyme activity (around 10%) with a lower dose (0.25 mg protein) and high inhibition of enzyme activity (around 80%) when a high dose of inhibitor was used (1.5 mg protein). The enzyme kinetic studies using Michaelis-Menten and Lineweaver-Burk equations showed the K(m) remained constant (0.58%) but the maximum velocity (V(max)) decreased in the presence of a crude extract of Triticale inhibitors, indicating mixed inhibition. The temperature giving 50% inactivation of enzyme (T(50)) during a 30-min incubation at pH 7.0 was 73° C. The maximum inhibitory activity was achieved at 35° C and pH 5.0. Gel assays showed the meaningful inhibition of E. integriceps α-amylases by various concentrations of Triticale inhibitors. Based on the data presented in this study, it could be said that the T-αAI has good inhibitory activity on E. integriceps gut α-amylase.

Characterization of a novel legumin alpha-amylase inhibitor from chickpea (Cicer arietinum L.) seeds

A proteinaceous alpha-amylase inhibitor (CLAI) was purified from Cicer arietinum seeds. It had a molecular mass of 25.947 kDa and inhibited alpha-amylases from plants and mammals. Analysis of the amino acid sequence of a polypeptide from CLAI showed that it was different from other known alpha-amylase inhibitors, but had high identity to legumins from Cicer arietinum (100%) and Vicia faba var. minor (90%).

The nutraceutical role of thePhaseolus vulgarisα-amylase inhibitor

The present review assesses the potential of thePhaseolus vulgarisα-amylase inhibitor isoform 1 (α-AI1) starch blockers as a widely used remedy against obesity and diabetes. Consumption of the α-amylase inhibitor causes marginal intraluminal α-amylase activity facilitated by the inhibitor's appropriate structural, physico-chemical and functional properties. As a result there is decreased postprandial plasma hyperglycaemia and insulin levels, increased resistance of starch to digestion and increased activity of colorectal bacteria. The efficacy and safety of the amylase inhibitor extracts, however, depend on the processing and extraction techniques used. The extracts are potential ingredients in foods for increased carbohydrate tolerance in diabetics, decreased energy intake for reducing obesity and for increased resistant starch. Research developments in the distribution and biosynthesis of the α-amylase inhibitor, relevant physico-chemical properties, the molecular starch-blocking mechanism, anti-obesity and anti-diabetes effects, safety of extracts and the need for research into their potential anti-colorectal cancer effect are discussed.

A Bowman-Birk trypsin inhibitor with antiproliferative activity from Hokkaido large black soybeans

A trypsin inhibitor, with an N-terminal sequence highly homologous to those of 8-kDa Bowman-Birk trypsin inhibitors, was isolated from the seeds of Hokkaido large black soybeans. The trypsin inhibitor was unadsorbed on SP-Sepharose but adsorbed on DEAE-cellulose and Mono Q. It inhibited proliferation in breast cancer (MCF-7) cells and hepatoma (Hep G2) cells with an IC50 of 35 and 140 microM, respectively. The trypsin inhibitory activity of the inhibitor was completely preserved after exposure to temperatures up to 100 degrees C for 30 min and to the pH range 2-13 for the same duration. The trypsin inhibitor inhibited HIV-1 reverse transcriptase with an IC50 of 38 microM, but was devoid of antifungal activity toward Fusarium oxysporum and Mycosphaerella arachidicola.

Characterization of alpha-amylase inhibitor from Palo Fierro seeds

Alpha amylase inhibitor from Palo Fierro seeds (alphaAI-PF) was purified using affinity chromatography on a fetuin-fractogel column followed by anionic exchange chromatography. AlphaAI-PF has a molecular mass of 77kDa with two subunits (15.8 and 17.4 kDa), it is nonglycosylated and has pI of 4.7. AlphaAI-PF inhibited porcine pancreatic alpha-amylase (PPA) (1,4-alpha-D-glucan glucanohydrolase; EC 3.2.1.1), but was almost devoid of inhibitory activity on alpha-amylase extracts from Zabrotes subfasciatus (ZSA). Analysis of alphaAI-PF peptides showed a high homology to alphaAI-1 from Phaseolus vulgaris that also inhibits PPA.

Cloning and characterization of α-amylase from Atlantic salmon (Salmo salar L.)

Amylase has a lower activity in carnivorous fish species, particularly in Atlantic salmon. We report the first cloning of a salmonid alpha-amylase cDNA from Atlantic salmon, a major species in aquaculture. By amino acid alignment of several species, we identified a seven amino acid deletion in one of the large loops of the enzyme in relatively close proximity to the active site, that could impair substrate binding. We also found the signal peptide to be less hydrophobic compared to other species. This may affect import into ER during protein synthesis. Active site residues were shown to be conserved. Amylase mRNA expression was shown in pancreatic tissue, liver, and in the heart. Using blocked p-nitrophenyl-maltoheptaoside as a substrate, we measured a low amylase activity in Atlantic salmon intestinal content, which was about half of the activity measured in Atlantic cod, whereas activity measured in rainbow trout was fourteen times higher. Amylase activities in all three species showed similar degree of reduction in hydrolytic activity in a dose-response trial with a wheat amylase inhibitor preparation. This indicates similar specific activity per amylase molecule.

Hypoglycaemic and anorexigenic activities of an alpha-amylase inhibitor from white kidney beans (Phaseolus vulgaris) in Wistar rats

An inhibitor of alpha-amylase was isolated and purified from an extract of white kidney beans (Phaseolus vulgaris). The acute oral administration of the inhibitor (50 mg/kg body weight) to adult Wistar rats together with a starch load (2 g/kg body weight suspended in NaCl (9 g/l)) reduced the increase in glycaemia over the basal value (NaCl, 222 (SEM 49); inhibitor, 145 (SEM 16) mmol/l x 180 min; P<0.05) without modifying the insulin response. On administering the inhibitor orally (50 mg/kg body weight dissolved in NaCl (9 g/l)) for 21 d to rats fed on a standard diet, a decline was observed in the glycaemia values on day 0 (NaCl, 5.53 (SEM 0.12); inhibitor, 5.25 (SEM 0.16) mmol/l) relative to those obtained on days 10 (NaCl, 5.00 (SEM 0.14); inhibitor, 4.60 (SEM 0.08) mmol/l; P<0.05) and 21 (NaCl, 5.22 (SEM 0.22); inhibitor, 4.50 (SEM 0.12) mmol/l; P<0.01) of treatment, without modifying the plasma concentration of insulin. There was found to be a significant anorexigenic action of the inhibitor; there was reduced food intake (NaCl, 23.07 (SEM 0.31); inhibitor, 19.50 (SEM 0.49) g/d; P<0.01), a reduced weight gain (NaCl, 52 (SEM 3); inhibitor, -1.33 (SEM 8.9) g/21 d; P<0.01), as well as changes in the activity of some intestinal enzymes such as maltase (NaCl, 87 (SEM 7); inhibitor, 127 (SEM 11) U/g proteins; P<0.05). The present study has shown, for the first time, that the prolonged administration of an alpha-amylase inhibitor reduces blood glucose levels and body-weight gain in Wistar rats.

Antifungal peptides, a heat shock protein-like peptide, and a serine-threonine kinase-like protein from Ceylon spinach seeds

Two antifungal peptides (designated alpha- and beta-basrubrins) with molecular masses of 4-5 kDa and distinct N-terminal sequences, and a peptide and a protein with N-terminal sequences resembling heat shock protein (hsp) and serine-threonine kinase, respectively, were isolated from seeds of the Ceylon spinach Basella rubra. The purification procedure entailed saline extraction, (NH4)2SO4 precipitation, ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, ion exchange chromatography on CM-cellulose, and FPLC-gel filtration on a Superdex peptide column. alpha- and beta-basrubrins inhibited mycelial growth in Botrytis cirerea with an IC50 value of 7.5 and 14.7 microM, respectively, Mycosphaerella arachidicola with an IC50 of 12.4 and 6.9 microM, and Fusarium oxysporum with an IC50 of 5.8 and 6.2 microM. Neither alpha-basrubrin nor beta-basrubin exhibited DNase, RNase, lectin or protease activity, indicating that their antifungal action is not due to these activities. HIV-1 reverse transcriptase was inhibited by alpha- and beta-basrubrins with an IC50 of 246 and 370 microM, respectively. Translation in rabbit reticulocyte lysate was inhibited by alpha- and beta-basrubrins with an IC50 of 400 and 100 nM. The heat shock protein-like peptide and serine-threonine kinase-like protein exhibited a molecular mass of 3 and 30 kDa, respectively. They inhibited neither translation in a rabbit reticulocyte system at concentrations up to 50 microM nor HIV-1 reverse transcriptase activity at concentrations up to 400 microM. They did not exert antifungal activity toward B. cinerea, M. arachidicola, and F. oxysporum when tested up to 16 microg. None of the aforementioned proteins demonstrated DNase, RNase, protease or lectin activity.

Potential physiological role of plant glycosidase inhibitors

Carbohydrate-active enzymes including glycosidases, transglycosidases, glycosyltransferases, polysaccharide lyases and carbohydrate esterases are responsible for the enzymatic processing of carbohydrates in plants. A number of carbohydrate-active enzymes are produced by microbial pathogens and insects responsible of severe crop losses. Plants have evolved proteinaceous inhibitors to modulate the activity of several of these enzymes. The continuing discovery of new inhibitors indicates that this research area is still unexplored and may lead to new exciting developments. To date, the role of the inhibitors is not completely understood. Here we review recent results obtained on the best characterised inhibitors, pointing to their possible biological role in vivo. Results recently obtained with plant transformation technology indicate that this class of inhibitors has potential biotechnological applications.

Porcine pancreatic α-amylase inhibition by the kidney bean (Phaseolus vulgaris) inhibitor (α-AI1) and structural changes in the α-amylase inhibitor complex

Porcine pancreatic alpha-amylase (PPA) is inhibited by the red kidney bean (Phaseolus vulgaris) inhibitor alpha-AI1 [Eur. J. Biochem. 265 (1999) 20]. Inhibition kinetics were carried out using DP 4900-amylose and maltopentaose as substrate. As shown by graphical and statistical analysis of the kinetic data, the inhibitory mode is of the mixed noncompetitive type whatever the substrate thus involving the EI, EI2, ESI and ESI2 complexes. This contrast with the E2I complex obtained in the crystal and with biophysical studies. Such difference very likely depends on the [I]/[E] ratio. At low ratio, the E2I complex is favoured; at high ratio the EI, ESI and EI2 complexes are formed. The inhibition model also differs from those previously proposed for acarbose [Eur. J. Biochem. 241 (1996) 787 and Eur. J. Biochem. 252 (1998) 100]. In particular, with alpha-AI1, the inhibition takes place only when PPA and alpha-AI are preincubated together before adding the substrate. This indicates that the abortive PPA-alphaAI1 complex is formed during the preincubation period. One additional carbohydrate binding site is also demonstrated yielding the ESI complex. Also, a second protein binding site is found in EI2 and ESI2 abortive complexes. Conformational changes undergone by PPA upon alpha-AI1 binding are shown by higher sensitivity to subtilisin attack. From X-ray analysis of the alpha-AI1-PPA complex (E2I), the major interaction occurs with two hairpin loops L1 (residues 29-46) and L2 (residues 171-189) of alpha-AI1 protruding into the V-shaped active site of PPA. The hydrolysis of alpha-AI1 that accounts for the inhibitory activity is reported.

Purification of castamollin, a novel antifungal protein from Chinese chestnuts

A novel antifungal protein, designated castamollin, was isolated from Chinese chestnut (Castanea mollisima) seeds with a procedure involving ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, ion exchange chromatography on CM-Sepharose and FPLC-gel filtration on Superdex 75. Castamollin possessed a novel N-terminal sequence demonstrating little similarity to N-terminal sequences of Castanea sativa chitinase. Castamollin exhibited a molecular mass of 37kDa in gel filtration and SDS-PAGE. It inhibited the activity of human immunodeficiency virus-1 reverse transcriptase with an IC(50) of 7microM and translation in a cell-free rabbit reticulocyte lysate system with an IC(50) of 2.7microM. Castamollin displayed antifungal activity against Botrytis cinerea, Mycosphaerella arachidicola, Physalospora piricola, and Coprinus comatus but was devoid of lectin activity.

Isolation of a napin-like polypeptide with potent translation-inhibitory activity from Chinese cabbage (Brassica parachinensis cv green-stalked) seeds

A heterodimeric napin-like polypeptide was isolated from Brassica parachinensis seeds with a procedure involving ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, FPLC-ion exchange chromatography on Mono S and FPLC-gel filtration on Superdex 75. The N-terminal sequence of the 5 kDa subunit of the polypeptide (PAGPFRIPKKRKKEE) showed high homology with other 2S storage proteins like napins and albumins. The polypeptide potently inhibited translation in a cell free system with an IC50 of 6.2 nM. The translation-inhibiting activity of the polypeptide was relatively stable in the pH range 6-11 and in the temperature range 10-50 degrees C.

Isolation of a novel peroxidase from French bean legumes and first demonstration of antifungal activity of a non-milk peroxidase

A novel antifungal protein with its N-terminal sequence bearing similarity to the C-terminal sequences of peroxidases was isolated from French bean legumes. The protein, which possessed a molecular weight of 37 kDa, was adsorbed on Affi-gel blue gel and CM-Sepharose. The protein exhibited peroxidase activity with a Km of 58 microM and a Vmax of 3.36 U/nmol. Optimal peroxidase activity was found at 22 degrees C and pH 4. It exerted antifungal activity against a variety of fungal species including Coprinus comatus, Mycosphaerella arachidicola, Fusarium oxysporum and Botrytis cinerea. It inhibited the activities of alpha-glucosidase and beta-glucosidase but was without any inhibitory effect on HIV-1 reverse transcriptase.

Interactions defining the specificity between fungal xylanases and the xylanase-inhibiting protein XIP-I from wheat

We previously reported on the xylanase-inhibiting protein I (XIP-I) from wheat [McLauchlan, Garcia-Conesa, Williamson, Roza, Ravestein and Maat (1999), Biochem. J. 338, 441-446]. In the present study, we show that XIP-I inhibits family-10 and -11 fungal xylanases. The K(i) values for fungal xylanases ranged from 3.4 to 610 nM, but bacterial family-10 and -11 xylanases were not inhibited. Unlike many glycosidase inhibitors, XIP-I was not a slow-binding inhibitor of the Aspergillus niger xylanase. Isothermal titration calorimetry of the XIP-I-A. niger xylanase complex showed the formation of a stoichiometric (1:1) complex with a heat capacity change of -1.38 kJ x mol(-1) x K(-1), leading to a predicted buried surface area of approx. 2200+/-500 A(2) at the complex interface. For this complex with A. niger xylanase (K(i)=320 nM at pH 5.5), titration curves indicated that an observable interaction occurred at pH 4-7, and this was consistent with the pH profile of inhibition of activity. In contrast, the stronger complex between A. nidulans xylanase and XIP-I (K(i)=9 nM) led to an observable interaction across the entire pH range tested (3-9). Using surface plasmon resonance, we show that the differences in the binding affinity of XIP-I for A. niger and A. nidulans xylanase are due to a 200-fold lower dissociation rate k(off) for the latter, with only a small difference in association rate k(on).

Primary structures of alpha- and beta-subunits of alpha-amylase inhibitors from seeds of three cultivars of Phaseolus beans

The primary structures of three alpha-amylase inhibitors (TAI, DAI, and MAI-2) consisting of glycoprotein subunits alpha and beta from the respective seeds of three cultivars of Phaseolus beans, Toramame (Phaseolus vulgaris L.), Daifukumame (Phaseolus vulgaris L.), and Murasakihanamame (Phaseolus coccineus L.) were determined by sequencing the peptide fragments derived from their enzymatic digestions. Major sugar chains of the inhibitors were also assessed by analyzing glycopeptides in the enzymatic digests. The subunits, alpha and beta, were shown to be composed of 76 and 139 amino acid residues, respectively, in each inhibitor. The overall amino acid sequences of the inhibitors were slightly different from one another. Furthermore, the sequence of TAI was the same as that deduced from a cDNA clone encording alpha-amylase inhibitor-1 from the common bean (Phaseolus vulgaris L.). It was also revealed that there were two N-glycosylation sites in each alpha-subunit: PA-derivatives of the major N-glycans were estimated to be M6B at Asn(12) and M9A at Asn(65). Each beta-subunit of TAI and MAI-2 had two N-glycosylation sites, while the beta-subunit of DAI had only one site. The major N-glycans pyridylaminated were estimated to be M3X at Asn(63) in each beta-subunit and M3FX at Asn(83) in beta-subunits of TAI and MAI-2.

Novel antifungal peptides from Ceylon spinach seeds

Two novel antifungal peptides, designated alpha- and beta-basrubrins, respectively, were isolated from seeds of the Ceylon spinach Basella rubra. The purification procedure involved saline extraction, (NH(4))(2)SO(4) precipitation, ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, ion exchange chromatography on CM-cellulose and FPLC-gel filtration on Superdex peptide column. alpha- and beta-basrubrins exhibited a molecular weight of 4.3 and 5 kDa, respectively. They inhibited translation in a rabbit reticulocyte system with an IC(50) value of 400 and 100 nM, respectively. alpha- and beta-basrubrin inhibited HIV-1 reverse transcriptase by (79.4 +/- 7.8)% and (54.6 +/- 3.6)%, respectively, at a concentration of 400 microM, and (10.56 +/- 0.92)% and (2.12 +/- 0.81)%, respectively, at a concentration of 40 microM. Both alpha- and beta-basrubrins exerted potent antifungal activity toward Botrytis cinerea, Mycosphaerella arachidicola, and Fusarium oxysporum.

Isolation of a homodimeric lectin with antifungal and antiviral activities from red kidney bean (Phaseolus vulgaris) seeds

A homodimeric lectin adsorbed on Affi-gel blue gel and CM-Sepharose and possessing a molecular weight of 67 kDa was isolated from red kidney beans. The hemagglutinating activity of this lectin was inhibited by glycoproteins but not by simple sugars. The lectin manifested inhibitory activity on human immunodeficiency virus-1 reverse transcriptase and alpha-glucosidase. The N-terminal sequence of the lectin exhibited some differences from previously reported lectins from Phaseolus vulgaris but showed some similarity to chitinases. It exerted a suppressive effect on growth of the fungal species Fusarium oxysporum, Coprinus comatus, and Rhizoctonia solani. The lectin had low ribonuclease and negligible translation-inhibitory activities.

Purification of chrysancorin, a novel antifungal protein with mitogenic activity from garland chrysanthemum seeds

A novel antifungal protein, designated chrysancorin, was isolated from seeds of Chrysanthemum coronarium var. spatiosum with a procedure involving ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue resin, ion exchange chromatography on SP-Sepharose and FPLC-gel filtration on Superdex 75. The N-terminus of chrysancorin displays sequence similarity to the genomic sequence of chromosome 1 from Arabidopsis thaliana BAC T19E23. Chrysancorin exhibits a molecular mass of 13.4 kDa in gel filtration and SDS-polyacrylamide gel electrophoresis. It stimulates the proliferation of mouse splenocytes and inhibits the activity of human immunodeficiency virus-1 reverse transcriptase. The protein possesses antifungal activity against Botrytis cinerea, Mycosphaerella arachidicola and Physalospora piricola, but not against Rhizoctonia solani, Fusarium oxysporum and Coprinus comatus. However, we could not detect antibacterial activity against a variety of bacteria.

Effect of certain plant extracts on alpha-amylase activity

Ethanolic extracts of Punica granatum, Mangifera indica, Boerhaavia diffusa, Embelia ribes, Phyllanthus maderaspatensis, and Withania somnifera, were tested for their effect on alpha-amylase activity (in vitro). P. granatum and M. indica were found to exhibit interesting alpha-amylase inhibitory activity.