Optimal designing of beta-conglycinin to genetically incorporate RPLKPW, a potent anti-hypertensive peptide

Hypotensive peptides derived from plant proteins

Hypertension is a risk factor for arteriosclerosis development and is recognized as a silent killer. Certain processed food materials, digested by protease or through the use of fermentation, have shown exertion of hypotensive effects in human clinical or animal studies, and hypotensive peptides were isolated from them. This review discusses the hypotensive peptides derived from plant proteins, such as grain, soy, vegetables, and seaweeds, and their hypotensive mechanisms. Although angiotensin I-converting enzyme (ACE) inhibition is often noted as one of the mechanisms that may exert antihypertensive effects, ACE inhibitory activity measured by in vitro studies is not associated with the actual hypotensive effect. Thus, this review only highlights the peptide hypotensive effect determined by in vivo studies. This review also discusses the tendency of the amino acid sequence of ACE-inhibitory hypotensive peptides and the possible additional effects of hypotensive peptides independent of ACE inhibition.

Current genetic engineering strategies for the production of antihypertensive ACEI peptides

Hypertension is a major and highly prevalent risk factor for various diseases. Among the most frequently prescribed antihypertensive first-line drugs are synthetic angiotensin I-converting enzyme inhibitors (ACEI). However, since  their use in hypertension therapy has been linked to various side effects, interest in the application of food-derived ACEI peptides (ACEIp) as antihypertensive agents is rapidly growing. Although promising, the industrial production of ACEIp through conventional methods such as chemical synthesis or enzymatic hydrolysis of food proteins has been proven troublesome. We here provide an overview of current antihypertensive therapeutics, focusing on ACEI, and illustrate how biotechnology and bioengineering can overcome the limitations of ACEIp large-scale production. Latest advances in ACEIp research and current genetic engineering-based strategies for heterologous production of ACEIp (and precursors) are also presented. Cloning approaches include tandem repeats of single ACEIp, ACEIp fusion to proteins/polypeptides, joining multivariate ACEIp into bioactive polypeptides, and producing ACEIp-containing modified plant storage proteins. Although bacteria have been privileged ACEIp heterologous hosts, particularly when testing for new genetic engineering strategies, plants and microalgae-based platforms are now emerging. Besides being generally safer, cost-effective and scalable, these "pharming" platforms can perform therelevant posttranslational modifications and produce (and eventually deliver) biologically active protein/peptide-based antihypertensive medicines.

Insertion of antihypertensive peptides in acidic subunit from amaranth 11S induces contrasting effects in stability

The insertion of peptides is a biotechnology tool widely used to improve the nutraceutical properties of proteins. Because the effect of these insertions in protein stability and function is difficult to predict, it should be determined experimentally. In this study, we created two variants of amarantin acidic subunit and analyzed them along with other four proteins reported previously. We measured their response against two destabilizing agents: temperature and urea. The six proteins presented the insertion of antihypertensive peptides (VYVYVYVY or RIPP) in the variable regions of the protein. We observed that their effect strongly depended on the site of the insertion. The insertion in the variable region I stabilized the protein both thermally and chemically, but it affected the inhibitory activity of the angiotensin-converting enzyme in vitro. In contrast, insertions in other three regions were severely destabilizing, producing molten globules. Our findings reveal that the insertion of bioactive peptides in variable regions of a protein can increase or decrease the protein's thermal and chemical stability and that these conformational changes may also alter its final activity.

Bioactivity of an antihypertensive peptide expressed in Chlamydomonas reinhardtii

In this study, we developed a transplastomic C. reinhardtii strain that accumulates anti-hypertensive peptides. Tandem repeats of VLPVP peptide were included. PCR analysis confirmed the presence of the transgene in the modified strains. After in vitro digestion of biomass of a recombinant C. reinhardtii strain the VLVPV peptide was identified and quantified by HPLC. The highest expression line produced 0.292mg of recombinant protein per mg of freeze-dried biomass. Intragastric administration of the genetically modified strain to spontaneous hypertensive rats at a dose of 30mg/kg of body weight of recombinant protein significantly reduced systolic blood pressure. At the same dose, the recombinant protein exerts an ACE-inhibitory effect. This is the first study that indicates the potential of this microalga producing an antihypertensive peptide as a dietary supplement for hypertension patients.

Bioactive peptides derived from natural proteins with respect to diversity of their receptors and physiological effects

We have found various bioactive peptides derived from animal and plant proteins, which interact with receptors for endogenous bioactive peptides such as opioids, neurotensin, complements C3a and C5a, oxytocin, and formyl peptides etc. Among them, rubiscolin, a δ opioid peptide derived from plant RuBisCO, showed memory-consolidating, anxiolytic-like, and food intake-modulating effects. Soymorphin, a μ opioid peptide derived from β-conglycinin showed anxiolytic-like, anorexigenic, hypoglycemic, and hypotriglyceridemic effects. β-Lactotensin derived from β-lactoglobulin, the first natural ligand for the NTS2 receptor, showed memory-consolidating, anxiolytic-like, and hypocholesterolemic effects. Weak agonist peptides for the complements C3a and C5a receptors were released from many proteins and exerted various central effects. Peptides showing anxiolytic-like antihypertensive and anti-alopecia effects via different types of receptors such as OT, FPR and AT2 were also obtained. Based on these study, new functions and post-receptor mechanisms of receptor commom to endogenous and exogenous bioactive peptides have been clarified.

The use of rice seeds to produce human pharmaceuticals for oral therapy

Rice (Oryza sativa L.) is the major staple food consumed by half of the world's population. Rice seeds have gained recent attention as bioreactors for the production of human pharmaceuticals such as therapeutic proteins or peptides. Rice seed production platforms have many advantages over animal cell or microbe systems in terms of cost-effectiveness, scalability, safety, product stability and productivity. Rice seed-based human pharmaceuticals are expected to become innovative therapies as edible drugs. Therapeutic proteins can be sequestered within natural cellular compartments in rice seeds and protected from harsh gastrointestinal environments. This review presents the state-of-the-art on the construction of gene cassettes for accumulation of pharmaceutical proteins or peptides in rice seeds, the generation of transgenic rice plants, and challenges involved in the use of rice seeds to produce human pharmaceuticals.

Expression of OsBiP4 and OsBiP5 is highly correlated with the endoplasmic reticulum stress response in rice

Binding protein (BiP) is a chaperone protein involved in the folding of secretory proteins in the ER lumen. OsBiP1 is constitutively expressed in various tissues, whereas the expression of OsBiP4 and OsBiP5 (OsBiP4&5) is not detected in any tissue under normal conditions. However, expression of OsBiP4&5 was highly and specifically activated under ER stress conditions induced by DTT treatment, OsBiP1 knockdown, OsBiP1 overexpression, OsIRE1 overexpression, or various exogenous recombinant proteins in transgenic rice. In contrast, OsBiP4&5 did not accumulate in OsIRE1 knockdown transgenic rice even after DTT treatment. When the subcellular localization of OsBiP4&5 was investigated in seed endosperm cells under the ER stress condition, OsBiP4&5 were localized to the ER, but did not participate in ER-derived protein body (PB-I) formation in a different manner to OsBiP1. These results indicate that OsBiP4&5 levels were positively correlated with stress levels in the ER. Taken together, these results suggest that OsBiP4&5 are ER stress-related BiP proteins that are regulated by OsIRE1/OsbZIP50 pathway and that they may have a distinct function from that of OsBiP1 in rice.

Antihypertensive activity of transgenic rice seed containing an 18-repeat novokinin peptide localized in the nucleolus of endosperm cells

Novokinin (Arg-Pro-Leu-Lys-Pro-Trp, RPLKPW) is a new potent antihypertensive peptide based on the sequence of ovokinin (2-7) derived from ovalbumin. We previously generated transgenic rice seeds in which eight novokinin were fused to storage protein glutelins (GluA2 and GluC) for expression. Oral administration of these seeds to spontaneously hypertensive rats (SHRs) reduced systolic blood pressures at a dose of 1 g seed/kg of SHR. Here, 10- or 18-tandem repeats of novokinin with an endoplasmic reticulum (ER) retention signal (Lys-Asp-Glu-Leu, KDEL) at the C terminus were directly expressed in rice under the control of the glutelin promoter containing its signal peptide. Only small amounts of the 18-repeat novokinin accumulated, and it was unexpectedly deposited in the nucleolus. This abnormal intracellular localization was explained by an endogenous signal for nuclear localization. The GFP reporter protein fused to this sequence targeted to nuclei by a transient assay using onion epidermal cells. Transgenic seed expressing the 18-repeat novokinin exhibited significantly higher antihypertensive activity after a single oral dose to SHR even at one-quarter the amount (0.25 g/kg) of the transgenic rice seed expressing the fusion construct; though, its novokinin content was much lower (1/5). Furthermore, in a long-term administration for 5 weeks, even a smaller dose (0.0625 g/kg) of transgenic seeds could confer antihypertensive activity. This high antihypertensive activity may be attributed to differences in digestibility of expressed products by gastrointestinal enzymes and the unique intracellular localization. These results indicate that accumulation of novokinin as a tandemly repeated structure in transgenic rice is more effective than as a fusion-type structure.

The hypocholesterolemic activity of transgenic rice seed accumulating lactostatin, a bioactive peptide derived from bovine milk β-lactoglobulin

Lactostatin is a novel pentapeptide (IIAEK) derived from bovine milk β-lactoglobulin with greater hypocholesterolemic activity than β-sitosterol, the drug commonly used to treat hypercholesterolemia. We developed transgenic rice expressing lactostatin as a fusion protein with seed storage protein (SSP) glutelins under the control of three different endosperm-specific promoters. Lactostatin accumulated in transgenic rice seed at approximately 1.6 mg/g seeds (dry seeds) without any apparent influence on seed traits such as endogenous SSP expression levels or alterations in the intracellular structures of endosperm cells. Short-term (three day) oral administration of the glutelin fraction containing lactostatin (namely three times of 300 mg/kg body weight/day) extracted from transgenic rice seeds resulted in hypocholesterolemic activity in rats; namely, the serum low-density-lipoprotein (LDL) cholesterol level was significantly reduced accompanied by a significant increase in beneficial serum high-density-lipoprotein (HDL) cholesterol.

Tandem multimer expression of angiotensin I-converting enzyme inhibitory peptide in Escherichia coli

It is common for small tandem peptide multimer genes to be indirectly inserted into expression vectors and fused with a protein tag. In this study, a multimer of the tandem angiotensin I-converting enzyme inhibitory peptide (ACE-IP) gene was directly transferred to a commercially available vector and the designed gene was expressed as a repeated peptide in Escherichia coli BL21(DE3)pLysS. The process further developed in our study was the construction of six-repeated ACE-IP synthetic genes and their direct insertion. Protein expression in inclusion bodies was confirmed by SDS-PAGE and Western blot. Acid hydrolysis of inclusion bodies produced single-unit peptides through cleavage of the aspartyl-prolyl bonds. This cleaved recombinant peptide (rACE-IP) was purified using immuno-affinity chromatography followed by reversed phase-HPLC. 105-115 mg of the lyophilized recombinant peptide was obtained from 1 L E. coli culture. In vitro biological activity of rACE-IP was indistinguishable from that of the natural peptide produced by hydrolysis in artificial gastric juice or by acidic hydrolysis. The rACE-IP prepared by recombinant DNA technology and solid-phase synthesis methods showed a similar IC(50). This strategy could be used for the expression of important peptides, which have N-terminal proline (P) and C-terminal aspartic acid residues (D) for commercial applications, e.g. functional foods and drinks.

Production of a bioactive peptide (IIAEK) in Escherichia coli using soybean proglycinin A1ab1b as a carrier

To produce large amounts of a peptide of fewer than 10 amino acid residues, construction of a gene encoding multimers of the small peptide is necessary. For this study a method was developed to facilitate the gene construction of high multimers of a small peptide with one step of cloning. A hypocholesterolemic peptide, IIAEK, from cow's milk beta-lactoglobulin was used as a model peptide for the construction of a gene encoding multimers of IIAEK and for the production of the peptide. Two systems for direct expression of 28-mers of IIAEK sequences (28IIAEK) and expression of 34 IIAEK sequences (4 IIAEK sequences in each of the disordered regions I, II, and III and 14 and 8 IIAEK sequences in disordered regions IV and V, respectively) in a mutant of soybean proglycinin A1aB1b lacking 31 residues in disordered region IV [A1aB1b(Delta31)-34IIAEK] were used. The protein produced from both systems formed inclusion bodies. The expression level of A1aB1b(Delta31)-34IIAEK was 29.9% of the total cell proteins and that of the 28IIAEK was 2.0%. The insoluble A1aB1b(Delta31)-34IIAEK was digested by trypsin without any help from urea or chemicals, and the produced IIAEK was purified using an octadecyl silica column. The yield of IIAEK was 58.6%. The results showed that A1aB1b as a carrier of multiple peptides and use of an Escherichia coli expression system are suitable for production of bioactive peptide.

Reduced mammary tumor progression in a transgenic mouse model fed an isoflavone-poor soy protein concentrate

Dietary exposure to soy has been associated with reduced breast cancer incidence. Soy isoflavones and protein components, such as protease inhibitors and the lunasin peptide, have been indicated as potential agents reducing carcinogenesis. In this study, the effect of soy-based diets was evaluated in a transgenic mouse model of breast carcinoma, overexpressing the neu oncogene. Neu female mice were fed for 20 wk a soy- and isoflavone-free diet (IFD), 4RF21 laboratory mouse diet, soy-based, thus isoflavone-rich (STD), or AIN-76-based semisynthetic diets with a soy protein isolate (SPI) or an isoflavone-poor soy protein concentrate (IPSP) as protein source. Mice were then sacrificed and tumors removed. Mammary tumor weights were not different in SPI versus IFD and STD fed mice. In contrast, mice fed IPSP showed reduced tumor progression versus IFD and STD groups (p < 0.05). Moreover, IPSP fed mice showed lower bromo-2'-deoxyuridine (BrdU) incorporation into breast tumor cells compared to STD and SPI fed animals (p < 0.02). Lung metastases were detected in 80% of IFD fed mice, in 70% of mice fed STD and SPI, and only in 50% of the IPSP fed animals. These results indicate that a diet containing an isoflavone-poor soy protein concentrate may inhibit breast tumor progression and metastasis development.

Accumulation of the bioactive peptides, novokinin, LPYPR and rubiscolin, in seeds of genetically modified soybean

Novokinin (RPLKPW), LPYPR, and rubiscolin (YPLDLF) are bioactive peptides with respective hypotensive, hypocholesterolemic, and memory-enhancing activities. We generated transgenic soybean lines that expressed modified forms of the alpha' subunit of seed storage protein beta-conglycinin containing tandem repeats of these bioactive peptides. The modified alpha' subunits constituted up to 0.2% of extracted proteins from the transgenic seeds.

Anti-hypertensive activity of genetically modified soybean seeds accumulating novokinin

Novokinin (Arg-Pro-Leu-Lys-Pro-Trp), which has been designed based on the structure of ovokinin (2-7), significantly reduces the systolic blood pressure at a dose of 100 microg/kg after oral administration in spontaneously hypertensive rats (SHRs). In this study, we generated a transgenic soybean which accumulates novokinin. A vector encoding a modified beta-conglycinin alpha' subunit (4novokinin-alpha') in which four novokinin sequences have been incorporated by site-directed mutagenesis was introduced into somatic embryos by whisker-mediated gene transformation to produce a transgenic soybean. The 4novokinin-alpha' occupied 0.5% of total soluble protein and 5% of the beta-conglycinin alpha' subunit in the transgenic soybean seeds. Protein extracted from the transgenic soybean reduced systolic blood pressure after single oral administration in SHRs at a dose of 0.15 g/kg. Defatted flour from the transgenic soybean also reduced the systolic blood pressure at a dose of 0.25 g/kg. Thus, the 4novokinin-alpha' produced in soybean exhibited an anti-hypertensive activity in SHRs after oral administration.

Agrobacterium-mediated transformation of a low glutelin mutant of 'Koshihikari' rice variety using the mutated-acetolactate synthase gene derived from rice genome as a selectable marker

We have developed an efficient rice transformation system that uses only rice genome-derived components. The transgenic 'Koshihikari' rice, low-glutelin mutant a123, is capable of accumulating large amounts of bioactive peptides in the endosperm. Agrobacterium-mediated transformation using the mutated-acetolactate synthase (mALS) gene expressed under the control of the callus-specific promoter (CSP) as a selectable marker was used to introduce GFP and an anti-hypertensive hexapeptide into 'Koshihikari' a123. The CSP:mALS gene cassette confers pyrimidinyl carboxy herbicide resistance to transgenic rice callus, but is not expressed in regenerated plants. Transformation efficiency of transgenic rice line a123 was improved from about 10% to about 30% by modifying callus induction, callus selection and regeneration media conventionally used for rice tissue culture.

High accumulation of bioactive peptide in transgenic rice seeds by expression of introduced multiple genes

We have developed a simple binary vector construction system for the simultaneous expression of multiple genes in plants. Up to three independent gene cassettes can be easily integrated into one binary vector using the MultiSite Gateway System. Using this system, we produced transgenic rice plants that accumulated high levels of the hypocholesterolaemic peptide lactostatin (IIAEK) in endosperm. Binary vectors were constructed that could accommodate up to three independent modified glutelin gene cassettes encoding multimer lactostatin in the variable regions. Eight construct permutations were used for rice transformation. We measured the accumulation of lactostatin expressed as a glutelin fusion protein in the mature seeds of 105 independent transgenic rice lines. A general correlation was observed between accumulation level and gene number in the vector constructs, indicating that a higher accumulation of lactostatin was obtained from transgenic rice plants containing the maximum number of gene inserts. These results indicate that this strategy is applicable for the selection of transgenic lines containing large amounts of bioactive peptides in rice seeds.

[Trp3, Arg5]-ghrelin(1-5) stimulates growth hormone secretion and food intake via growth hormone secretagogue (GHS) receptor

Ghrelin, a 28 amino acid peptide identified as an endogenous ligand for growth hormone secretagogue (GHS) receptor, stimulates food intake and growth hormone (GH) secretion. We designed low molecular weight peptides with affinity for the GHS receptor based on the primary structure of ghrelin. We found that [Trp3, Arg5]-ghrelin(1-5) (GSWFR), a novel pentapeptide composed of all L-amino acids, had affinity for the GHS receptor (IC50 = 10 microM). GSWFR stimulated GH secretion after intravenous or oral administration. Centrally administered GSWFR increased food intake in non-fasted mice. The orexigenic action of GSWFR was inhibited by a GHS receptor antagonist, [D-Lys3]-GH-releasing peptide-6, suggesting that GSWFR stimulated food intake through the GHS receptor. The orexigenic action of GSWFR was also inhibited by a neuropeptide Y (NPY) Y1 receptor antagonist, BIBO3304. These results suggest that the GSWFR-induced feeding is mediated by the NPY Y1 receptor.

Antihypertensive peptides derived from egg proteins

There have been studies of antihypertensive peptides derived from food proteins, but very few described the production of bioactive peptides from egg proteins. The first 2 antihypertensive peptides isolated in egg were obtained by enzymatic hydrolysis of ovalbumin. They correspond to the sequences Phe-Arg-Ala-Asp-His-Pro-Phe-Leu (ovokinin) and Arg-Ala-Asp-His-Phe-Leu (ovokinin 2-7). Both exhibited endothelium-dependent vasodilatory activity. Ovokinin (2-7) had higher antihypertensive potency than ovokinin in spontaneously hypertensive rats (SHR). Modifications in the sequence of ovokinin (2-7) improved the bioavailability of this peptide. It was also demonstrated that different ovalbumin hydrolysates can inhibit angiotensin I-converting enzyme (ACE). We recently obtained an egg white hydrolysate that inhibited the enzyme in vitro. It was obtained by treating egg white with pepsin and it exhibited antihypertensive activity in SHR. Some ACE-inhibitory peptides obtained from this hydrolysate (Tyr-Arg-Glu-Glu-Arg-Tyr-Pro-Ile-Leu, Arg-Ala-Asp-His-Pro-Phe-Leu, and Ile-Val-Phe) also showed antihypertensive activity in these rats. The egg products mentioned could be used as functional food ingredients with potential therapeutic benefit in the prevention and treatment of hypertension.

Design of genetically modified soybean proglycinin A1aB1b with multiple copies of bioactive peptide sequences

The peptide IIAEK derived from beta-lactoglobulin has a hypocholesterolemic activity greater than that of beta-sitosterol. To create food proteins with multiple copies of this valuable peptide sequence, we introduced tandem multimers of the nucleotide sequence encoding the peptide into DNA regions corresponding to the five variable regions of soybean glycinin A1aB1b subunit, and expressed the mutants in Escherichia coli. The expression level and solubility of the five mutants, each containing four IIAEK sequences in each of the variable regions, were compared. Overall, the expression level and solubility of the mutants with four IIAEK sequences in the variable regions IV and V were the best followed by II > III > I. Further, introduction of the fifth IIAEK sequence to the variable region IV did not decrease expression level and solubility. Increasing the number of IIAEK to 7 and 10 slightly decreased expression level, while their solubility decreased to as low as 40 and 1%, respectively. Various mutations were combined to get a mutant containing as many IIAEK sequences as possible. Some of the resulting mutants were expressed in the soluble form. The mutant containing eight IIAEK from the combination of variable regions IV and V (IV-4 + V-4) showed the best balance of the expression level and solubility, followed by the combination of variable regions II and III (II-4 + III-4). The soluble fractions of these mutants were purified by hydrophobic, gel filtration and ion-exchange column chromatography. Yields of IIAEK peptide released by in vitro digestion with trypsin from both mutants were around 80%. This is the first report that a large amount of a physiologically active peptide could be introduced into food protein.

A transgenic rice seed accumulating an anti-hypertensive peptide reduces the blood pressure of spontaneously hypertensive rats

RPLKPW is a potent anti-hypertensive peptide designed according to the structure of ovokinin(2-7) (RADHPF). In this study, we generated transgenic rice plants that accumulate the RPLKPW peptide as a fusion protein with the rice storage protein glutelin. The engineered peptide is expressed under the control of endosperm-specific glutelin promoters and specifically accumulates in seeds. Oral administration of either the RPLKPW-glutelin fraction or transgenic rice seeds to spontaneously hypertensive rats (SHRs) significantly reduced systolic blood pressures. These results suggest the possible application of transgenic rice seed as a nutraceutical delivery system and specifically for administration of active peptides in hypertension.

Grain legume proteins and nutraceutical properties

Grain legumes are a valuable source of food proteins. Their exploitation is expected to grow in relation of a growing world's food needs. Moreover, it is currently taking place a reappraisal of the beneficial effects of legume seed dietary intake, which are the basis for various health claims. Proteins and peptides concur to the observed biological activities of legume seeds, but their effect(s) has(ve) not completely been disclosed. Aims of this review are: to report the most relevant putative positive effects of grain legumes on human health and to give an account of the current knowledge on the demonstrated legume seed protein biological activities. Specific effects on the prevention and treatment of various diseases, mostly of which are typical of the affluent countries, are reported. Examples of studies at molecular level aimed at elucidating of the underlying mechanism(s) are given. The prospects on targeted legume protein exploitation in the nutraceutical area, including the biotechnological approaches, are also considered.