In silico structural characteristics and α-amylase inhibitory properties of Ric c 1 and Ric c 3, allergenic 2S albumins from Ricinus communis seeds

Production of a Ric c3 hypo-allergen with no IgE binding or anaphylactogenic activity

Several studies have been carried out to expand the use of Ricinus communis L. castor bean (Ricinus communis L castor bean.). This oilseed finds appropriate conditions for its development in Brazil, with more than 700 applications. The main allergens of this plant are Ric c1 and Ric c3, that cross-react with various aeroallergens and food allergens such as peanuts, soybeans, corn, and wheat. This study aimed to determine the effect of mutations in Ric c3 amino acid residues known to affect IgE binding and allergy challenges. Based on the Ric c3 structure, B-cell epitopes, and amino acid involved in IgE binding, we produce recombinant mutant protein, mrRic c3, secreted from E. coli. Strategic glutamic acid residues in IgE-biding regions were changed by Leucine. The allergenicity of mrRic c3 was evaluated by determination of IgE, IgG1, and total IgG in immunized Balb/c mice and by degranulation assays of mast cells isolated from Wistar rats. The mrRic c3 presented a percentage of mast cell degranulation close to that seen in the negative control, and the immunization of mice with mrRic c3 presented lower levels of IgE and IgG1 than the group treated with the protein without mutations. The mutant mrRic c3 had an altered structure and reduced ability to stimulate pro-inflammatory responses and bind IgE but retained its ability to induce blocking antibodies. Thus, producing a hypoallergenic mutant allergen (mrRic c3) may be essential in developing new AIT strategies.

The forgotten 2S albumin proteins: Importance, structure, and biotechnological application in agriculture and human health

2S albumin proteins are a group of important seed storage proteins (SSPs) essential to seeds at early and late developmental stages, by providing amino acids and other nutrients during germination and for seed defense. 2S albumins possess a well-conserved cysteine supporting the stability of temperature, pH, and proteolysis. The 3D structure rich in alpha-helices and positively charged is particularly suited for antibacterial and antifungal activity, which is presented by many 2S albumins. However, the hypervariable region present in 2S albumins induces allergenic reactions. Because of that, 2S albumins have never been recognized for their biotechnological potential. However, the development of servers used for the rational design of antimicrobial molecules has now brought a new application to 2S albumins, acting as a model to design antimicrobial molecules without the toxic or allergenic effects of 2S albumins. Therefore, this review is focused on discussing the importance of 2S albumins to seed development and defense and the biochemical, structural and functional properties of these proteins thought to play a role in their antimicrobial activity. Additionally, the application of 2S albumins to design synthetic antimicrobial peptides is discussed, potentially bringing new functions to these forgotten proteins.

Ricin and Ricinus communis in pharmacology and toxicology-from ancient use and "Papyrus Ebers" to modern perspectives and "poisonous plant of the year 2018"

While probably originating from Africa, the plant Ricinus communis is found nowadays around the world, grown for industrial use as a source of castor oil production, wildly sprouting in many regions, or used as ornamental plant. As regards its pharmacological utility, a variety of medical purposes of selected parts of the plant, e.g., as a laxative, an anti-infective, or an anti-inflammatory drug, have been described already in the sixteenth century BC in the famous Papyrus Ebers (treasured in the Library of the University of Leipzig). Quite in contrast, on the toxicological side, the native plant has become the "poisonous plant 2018" in Germany. As of today, a number of isolated components of the plant/seeds have been characterized, including, e.g., castor oil, ricin, Ricinus communis agglutinin, ricinin, nudiflorin, and several allergenic compounds. This review mainly focuses on the most toxic protein, ricin D, classified as a type 2 ribosome-inactivating protein (RIP2). Ricin is one of the most potent and lethal substances known. It has been considered as an important bioweapon (categorized as a Category B agent (second-highest priority)) and an attractive agent for bioterroristic activities. On the other hand, ricin presents great potential, e.g., as an anti-cancer agent or in cell-based research, and is even explored in the context of nanoparticle formulations in tumor therapy. This review provides a comprehensive overview of the pharmacology and toxicology-related body of knowledge on ricin. Toxicokinetic/toxicodynamic aspects of ricin poisoning and possibilities for analytical detection and therapeutic use are summarized as well.

A modified, hypoallergenic variant of the Ricinus communis Ric c1 protein retains biological activity

Ric c1, an allergenic protein from Ricinus communis , is an insect α-amylase inhibitor that has become an occupational allergen. Ric c1 can cross-react with allergens from wheat, soybean, peanut, shrimp, fish, gluten, house dust, tobacco, and air fungus, thereby amplifying the concern and risks caused by Ricinus allergens. Two continuous IgE-binding epitopes were identified in Ric c1, both containing glutamic acid residues involved in IgE-binding and allergic challenges. We produced recombinant Ric c1 (rRic c1) in Escherichia coli , using primers from foliar R. communis DNA, and a mutant (Glu-Leu) recombinant protein (mrRic c1) in the same system using synthetic genes. rRic c1 preserved both allergenic and α-amylase inhibitory properties, and mrRic c1 drastically reduced allergenic properties. These results can help to establish meaningful relationships between structure, defense and allergenicity, important steps for producing engineered plants and developing new approaches for immunotherapy.

In Vitro and In Vivo Effects of α-Amylase Inhibitor From Avena sativa Seeds on Life History and Physiological Characteristics of Sitotroga cerealella (Lepidoptera: Gelechiidae)

The inhibitory effects of Avena sativa L. seed extract were studied on life history and some physiological aspects of Sitotroga cerealella (Olivier; Lepidoptera: Gelechiidae). The inhibition of α-amylase activity in vitro by A. sativa proteinaceous extract suggested its potential antimetabolic effect on S. cerealella larvae. Although, chronic ingestion of A. sativa inhibitor (I10: 0.108 mg protein/artificial seed) did not show significant reduction of the growth and development of S. cerealella. However, a delay in the developmental time of immature stages was detected when S. cerealella larvae were continuously fed on I30 and I50 concentrations (0.429 and 1.11 mg protein/artificial seed, respectively) of the inhibitor. The highest realized fecundity was recorded for females which came from larvae fed on I10 concentration (102.46 ± 2.50 eggs/female), and the lowest fecundity was observed for females which came from larvae fed on I50 concentration (31.64 ± 3.17 eggs/female). The lightest weight of pupae of S. cerealella was observed on I50 concentration (2.76 ± 0.07 mg). The lowest glycogen and lipid contents of the pupae were detected on I50 concentration (50.00 ± 3.53 and 289.57 ± 29.00 µg/pupa, respectively). The lower survival rate of pupae at low temperature indicated that S. cerealella fed on I50 concentration of the inhibitor was less cold tolerant than control insects. The inhibitory studies indicated that A. sativa proteinaceous extract is a good candidate as an inhibitor of the α-amylase of this pest. This inhibitor can be expressed in genetically engineered plants to confer resistance to S. cerealella.

Genomic and functional characterization of coleopteran insect-specific α-amylase inhibitor gene from Amaranthus species

The smallest 32 amino acid α-amylase inhibitor from Amaranthus hypochondriacus (AAI) is reported. The complete gene of pre-protein (AhAI) encoding a 26 amino acid (aa) signal peptide followed by the 43 aa region and the previously identified 32 aa peptide was cloned successfully. Three cysteine residues and one disulfide bond conserved within known α-amylase inhibitors were present in AhAI. Identical genomic and open reading frame was found to be present in close relatives of A. hypochondriacus namely Amaranthus paniculatus, Achyranthes aspera and Celosia argentea. Interestingly, the 3'UTR of AhAI varied in these species. The highest expression of AhAI was observed in A. hypochondriacus inflorescence; however, it was not detected in the seed. We hypothesized that the inhibitor expressed in leaves and inflorescence might be transported to the seeds. Sub-cellular localization studies clearly indicated the involvement of AhAI signal peptide in extracellular secretion. Full length rAhAI showed differential inhibition against α-amylases from human, insects, fungi and bacteria. Particularly, α-amylases from Helicoverpa armigera (Lepidoptera) were not inhibited by AhAI while Tribolium castaneum and Callosobruchus chinensis (Coleoptera) α-amylases were completely inhibited. Molecular docking of AhAI revealed tighter interactions with active site residues of T. castaneum α-amylase compared to C. chinensis α-amylase, which could be the rationale behind the disparity in their IC₅₀. Normal growth, development and adult emergence of C. chinensis were hampered after feeding on rAhAI. Altogether, the ability of AhAI to affect the growth of C. chinensis demonstrated its potential as an efficient bio-control agent, especially against stored grain pests.

A 2S Albumin from the Seed Cake of Ricinus communis Inhibits Trypsin and Has Strong Antibacterial Activity against Human Pathogenic Bacteria

Hospital-acquired infections caused by antibiotic-resistant bacteria threaten the lives of many citizens all over the world. Discovery of new agents to hinder bacterial development would have a significant impact on the treatment of infections. Here, the purification and characterization of Rc-2S-Alb, a protein that belongs to the 2S albumin family, from Ricinus communis seed cake, are reported. Rc-2S-Alb was purified after protein extraction with Tris-HCl buffer, pH 7.5, fractionation by ammonium sulfate (50-75%), and chromatography on Phenyl-Sepharose and DEAE-Sepharose. Rc-2S-Alb, a 75 kDa peptide, displays trypsin inhibitory activity and has high in vitro antibacterial activity against Bacillus subtilis, Klebsiella pneumonia, and Pseudomonas aeruginosa, which are important human pathogenic bacteria. Atomic force microscopy studies indicated that Rc-2S-Alb disrupts the bacterial membrane with loss of the cytoplasm content and ultimately bacterial death. Therefore, Rc-2S-Alb is a powerful candidate for the development of an alternative drug that may help reduce hospital-acquired infections.