A glycoprotein α-amylase inhibitor from Withania somnifera differentially inhibits various α-amylases and affects the growth and development of Tribolium castaneum

A Proteinaceous Alpha-Amylase Inhibitor from Moringa Oleifera Leaf Extract: Purification, Characterization, and Insecticide Effects against C. maculates Insect Larvae

The main objective of the current study was the extraction, purification, and enzymatic characterization of a potent proteinaceous amylase inhibitor from Moringa oleifera. The antimicrobial potential and insecticide effects against C. maculates insect larvae were also studied. The α-amylase inhibitor was extracted in methanol (with an inhibitory activity of 65.6% ± 4.93). Afterwards, the inhibitor αAI.Mol was purified after a heat treatment at 70 °C for 15 min followed by one chromatographic step of Sephadex G-50. An apparent molecular weight of 25 kDa was analyzed, and the N-terminal sequence showed the highest identity level (89%) with the monomeric α-amylase inhibitor from Triticum dicoccoides. αAI.Mol was found to tolerate pH values ranging from 5.0 to 11.0 and showed maximal activity at pH 9.0. Thermal stability was remarkably important, since the inhibitory activity was maintained at 55% after 1 h of incubation at 70 °C and at 53% after an incubation of 45 min at 80 °C. The potency of the current purified inhibitor against amylases from different origins indicates that αAI.Mol seems to possess the highest affinity toward human salivary α-amylase (90% inhibitory activity), followed by the α-amylase of insects Callosobruchus maculatus and Tribolium confusum (71% and 61%, respectively). The kinetic parameters were also calculated, and the Kmax and Vmax of the digestive amylase were estimated at 185 (mmol/min/mg) and 0.13 mM, respectively. The inhibitor possesses a strong bactericidal effect against Gram+ and Gram- strains, and the MIC values were >1 against B. cereus but >6 against E. coli. Interestingly, the rates of survival and pupation of C. maculates insect larvae were remarkably affected by the purified αAI.Mol from Moringa oleifera.

Characterization of a Bowman-Birk type trypsin inhibitor purified from seeds of Solanum surattense

A Bowman-Birk type trypsin inhibitor protein (SSTI) from seeds of the medicinal plant Solanum surattense was isolated, purified and characterized. SSTI showed a single band on SDS-PAGE corresponding to 11.4 kDa molecular weight. It is a glycoprotein (2.8% glycosylation) that differentially interacted with trypsin and chymotrypsin in a concentration-dependent manner. Its peptide sequence is similar to other Bowman-Birk type protease inhibitors found in Glycine max and Phaseolus acutifolius. The inhibitory activity was stable over a wide range of pH (1-10) and temperatures (10-100° C). Far-UV Circular Dichroism (CD) studies showed that SSTI contains β sheets (~ 23%) and α helix (~ 6%) and demonstrated structural stability at wide pH and high temperature. The kinetic analysis revealed a noncompetitive (mixed) type nature of SSTI and low inhibitor constant (Ki) values (16.6 × 10-8 M) suggested strong inhibitory activity. Isothermal titration calorimetric analysis revealed its high affinity towards trypsin with dissociation constant (Kd) 2.28 µM.

Natural edible materials made of protein-functionalized aerogel particles for postprandial hyperglycemia management

α-Amylase inhibitors (α-AIs) delay digestion of dietary starch by inhibiting α-amylase in the gut, thereby reducing the postprandial glycemia, which is beneficial to the patients with obesity and diabetes. The proteinaceous α-AIs from wheat can effectively control starch digestion and regulate postprandial hyperglycemia. However, their gastric intolerance remains a challenge, which limits its commercial production and industrial application. In this study, sodium alginate/chitosan aerogels loaded with wheat protein α-AIs were prepared and evaluated as potential transportation and protection matrices for important components in food or pharmaceutical applications. Specifically, the biodegradable aerogel cross-linked with sodium alginate-chitosan-calcium chloride, has a large surface area and open porous structure, which can adsorb staple wheat proteins as an integrated edible material to block around 88,660 U/g of α-amylase activity. The aerogel particles were able to protect the activity of wheat α-AIs in the stomach, leading to the slow passage of the wheat α-AIs through the small intestine to inhibit starch digestion more effectively. Animal experiments further showed that the postprandial blood glucose levels in rats were effectively controlled through delayed increase, after administration of wheat protein-functionalized aerogel particles loaded with wheat α-AIs, which are natural biological macromolecules. This is a novel, safe, and economical method for the prevention and pretreatment of diabetes.

The Amylases of Insects

Alpha-amylases are major digestive enzymes that act in the first step of maltopolysaccharide digestion. In insects, these enzymes have long been studied for applied as well as purely scientific purposes. In many species, amylases are produced by multiple gene copies. Rare species are devoid of Amy gene. They are predominantly secreted in the midgut but salivary expression is also frequent, with extraoral activity. Enzymological parameters are quite variable among insects, with visible trends according to phylogeny: Coleopteran amylases have acidic optimum activity, whereas dipteran amylases have neutral preference and lepidopteran ones have clear alkaline preference. The enzyme structure shows interesting variations shaped by evolutionary convergences, such as the recurrent loss of a loop involved in substrate handling. Many works have focused on the action of plant amylase inhibitors on pest insect amylases, in the frame of crop protection by transgenesis. It appears that sensitivity or resistance to inhibitors is finely tuned and very specific and that amylases and their inhibitors have coevolved. The multicopy feature of insect amylases appears to allow tissue-specific or stage-specific regulation, but also to broaden enzymological abilities, such as pH range, and to overcome plant inhibitory defenses.

Plant-Derived Substances Used Against Beetles-Pests of Stored Crops and Food-and Their Mode of Action: A Review

Plants are sources of numerous active substances that are used to protect crops. Currently, due to the limitations of using synthetic insecticides, plant products have attracted increasing attention as possible pesticides. In this review, we discuss some of the most interesting plant products (for example, Solanaceae, or Asteraceae extracts, Artemisia absinthium or Citrus spp. essential oils, and single compounds like α-chaconine, or α-solanine) that exhibit insecticidal activity against beetles that are pests of stored food products. Next, we describe and discuss the mode of action of these products, including lethal and sublethal effects, such as antifeedant or neurotoxic activity, ultrastructural malformation, and effects on prooxidant/antioxidant balance. Furthermore, the methods of application of plant-derived substances in food storage areas are presented.