Purification and characterization of a novel calcium-biding decapeptide from Pacific cod (Gadus Macrocephalus) bone: Molecular properties and calcium chelating modes

Isolation and differential structure characteristics of calcium-binding peptides derived from Pacific cod bones by hydroxyapatite affinity

Calcium-chelating peptides were found in Pacific cod bone, but their binding structure and properties have not been elucidated. Novel calcium-binding peptides were isolated by hydroxyapatite affinity chromatography (HAC), and their binding structure and properties were investigated by isothermal titration calorimetry (ITC), multispectral techniques, and mass spectrometry. Based on multiple purifications, the calcium binding capacity (CBC) of Pacific cod bone peptides (PBPs) was increased from 1.71 ± 0.15 μg/mg to 7.94 ± 1.56 μg/mg. Peptides with a molecular weight of 1-2 kDa are closely correlated with CBC. After binding to calcium, the secondary structure of peptides transitioned from random coil to β-sheet, resulting in a loose and porous microstructure. Hydrogen bonds, electrostatic interaction, and hydrophobic interaction contribute to the formation of peptide‑calcium complexes. The F21 contained 42 peptides, with repeated "GE" motif. Differential structure analysis provides a theoretical basis for the targeted preparation of high CBC peptides.

Isolation, identification, and chelation mechanism of ferrous-chelating peptide from peanut protein hydrolysate

BACKGROUND

Peanut peptides can chelate iron but their chelation mechanism remains unclear. The purpose of this study is to separate peanut ferrous-chelating peptides and explore the chelation mechanism of peanut peptides with iron.

RESULTS

Peanut peptide component F-122, which had a higher chelation rate, was separated using ultrafiltration, gel filtration chromatography, and ion exchange chromatography, achieving a ferrous chelation rate of 90.7%. Six peptide segments were screened and their amino acid sequences were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Spectral analysis confirmed that the chelation between peanut peptides and ferrous ions occurred and a new substance was formed. Molecular docking simulation indicated that the amino acids in peanut peptides involved in the chelating reaction were glutamic acid, arginine, glycine, threonine, phenylalanine, and lysine. The binding sites included the main chain oxygen atom, side chain oxygen atom, and carboxyl oxygen atom of amino acid.

CONCLUSION

The isolated peanut peptide had a higher ferrous-chelation rate. The chelating mechanism of peanut peptide with ferrous ion was elucidated. This study provides a theoretical basis for the development of new peptide-ferrous preparations. © 2024 Society of Chemical Industry.

Peptides Used for Heavy Metal Remediation: A Promising Approach

In recent years, heavy metal pollution has become increasingly prominent, severely damaging ecosystems and biodiversity, and posing a serious threat to human health. However, the results of current methods for heavy metal restoration are not satisfactory, so it is urgent to find a new and effective method. Peptides are the units that make up proteins, with small molecular weights and strong biological activities. They can effectively repair proteins by forming complexes, reducing heavy metal ions, activating the plant's antioxidant defense system, and promoting the growth and metabolism of microorganisms. Peptides show great potential for the remediation of heavy metal contamination due to their special structure and properties. This paper reviews the research progress in recent years on the use of peptides to remediate heavy metal pollution, describes the mechanisms and applications of remediation, and provides references for the remediation of heavy metal pollution.

Evaluating the capability of soybean peptides as calcium ion carriers: a study through sequence analysis and molecular dynamics simulations

Calcium homeostasis imbalance in the body can lead to a variety of chronic diseases. Supplement efficiency is essential. Peptide calcium chelate, a fourth-generation calcium supplement, offers easy absorption and minimal side effects. Its effectiveness relies on peptide's calcium binding capacity. However, research on amino acid sequences in peptides with high calcium binding capacity (HCBC) is limited, affecting the efficient identification of such peptides. This study used soybean peptides (SP), separated and purified by gel chromatography, to obtain HCBC peptide (137.45 μg mg-1) and normal peptide (≤95.78 μg mg-1). Mass spectrometry identified the sequences of these peptides, and an analysis of the positional distribution of characteristic amino acids followed. Two HCBC peptides with sequences GGDLVS (271.55 μg mg-1) and YEGVIL (272.54 μg mg-1) were discovered. Molecular dynamics showed that when either aspartic acid is located near the N-terminal's middle, or glutamic acid is near the end, or in cases of continuous Asp or Glu, the binding speed, probability, and strength between the peptide and calcium ions are superior compared to those at other locations. The study's goal was to clarify how the positions of characteristic amino acids in peptides affect calcium binding, aiding in developing peptide calcium chelates as a novel calcium supplement.

Screening, separation and identification of metal-chelating peptides for nutritional, cosmetics and pharmaceutical applications

Metal-chelating peptides, which form metal-peptide coordination complexes with various metal ions, can be used as biofunctional ingredients notably to enhance human health and prevent diseases. This review aims to discuss recent insights into food-derived metal-chelating peptides, the strategies set up for their discovery, their study, and identification. After understanding the overall properties of metal-chelating peptides, their production from food-derived protein sources and their potential applications will be discussed, particularly in nutritional, cosmetics and pharmaceutical fields. In addition, the review provides an overview of the last decades of progress in discovering food-derived metal-chelating peptides, addressing several screening, separation and identification methodologies. Furthermore, it emphasizes the methods used to assess peptide-metal interaction, allowing for better understanding of chemical and thermodynamic parameters associated with the formation of peptide-metal coordination complexes, as well as the specific amino acid residues that play important roles in the metal ion coordination.

Fabrication of peptide-encapsulated sodium alginate hydrogel for selective gallium adsorption

Peptides are recognized as promising adsorbents in metal selective recovery. In this study, the designed gallium-binding peptide H6GaBP was immobilized by the polysaccharide polymer sodium alginate (SA) for gallium recovery. The synthesized H6GaBP@SA microspheres exhibited a maximum adsorption capacity of 127.4 mg/g and demonstrated high selectivity for gallium at lower pH values. The adsorption process aligned well with the pseudo-second-order equation and Langmuir model. To elucidate the adsorption mechanism, a comprehensive characterization including molecular docking, scanning electron microscope coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and thermogravimetry analysis (TGA), were conducted. These analyses revealed that gallium ions were initially adsorbed through electrostatic interaction by H6GaBP@SA, followed by a cation exchange reaction between Ga(OH)2+ and Ca2+, as well as coordination between gallium and histidine residues on the peptide. Moreover, the H6GaBP@SA exhibited improved thermal stability compared to sole sodium alginate microspheres, and the coordination of gallium with peptides can also defer the decomposition rate of the adsorbents. Compared to other adsorbents, the peptide-encapsulated hydrogel microspheres exhibited superior gallium selectivity and improved adsorption capacity, offering an environmentally friendly option for gallium recovery.

Novel Ca-Chelating Peptides from Protein Hydrolysate of Antarctic Krill (Euphausia superba): Preparation, Characterization, and Calcium Absorption Efficiency in Caco-2 Cell Monolayer Model

Antarctic krill (Euphausia superba) is the world's largest resource of animal proteins and is thought to be a high-quality resource for future marine healthy foods and functional products. Therefore, Antarctic krill was degreased and separately hydrolyzed using flavourzyme, pepsin, papain, and alcalase. Protein hydrolysate (AKH) of Antarctic krill prepared by trypsin showed the highest Ca-chelating rate under the optimized chelating conditions: a pH of 8.0, reaction time of 50 min, temperature of 50 °C, and material/calcium ratio of 1:15. Subsequently, fourteen Ca-chelating peptides were isolated from APK by ultrafiltration and a series of chromatographic methods and identified as AK, EAR, AEA, VERG, VAS, GPK, SP, GPKG, APRGH, GVPG, LEPGP, LEKGA, FPPGR, and GEPG with molecular weights of 217.27, 374.40, 289.29, 459.50, 275.30, 300.36, 202.21, 357.41, 536.59, 328.37, 511.58, 516.60, 572.66, and 358.35 Da, respectively. Among fourteen Ca-chelating peptides, VERG presented the highest Ca-chelating ability. Ultraviolet spectrum (UV), Fourier Transform Infrared (FTIR), and scanning electron microscope (SEM) analysis indicated that the VERG-Ca chelate had a dense granular structure because the N-H, C=O and -COOH groups of VERG combined with Ca2+. Moreover, the VERG-Ca chelate is stable in gastrointestinal digestion and can significantly improve Ca transport in Caco-2 cell monolayer experiments, but phytate could significantly reduce the absorption of Ca derived from the VERG-Ca chelate. Therefore, Ca-chelating peptides from protein hydrolysate of Antarctic krill possess the potential to serve as a Ca supplement in developing healthy foods.

Preparation, Structural Characterization, and Stability of Low-Molecular-Weight Collagen Peptides-Calcium Chelate Derived from Tuna Bones

This study was conducted to prepare calcium chelate of low-molecular-weight tuna bone collagen peptides (TBCPLMW) with a high chelation rate and to identify its structural characteristics and stability. The optimum conditions for calcium chelation of TBCPLMW (TBCPLMW-Ca) were determined through single-factor experiments and response surface methodology, and the calcium-chelating capacity reached over 90% under the optimal conditions. The amino acid compositions implied that Asp and Glu played important roles in the formation of TBCPLMW-Ca. Structural characterizations determined via spectroscopic analyses revealed that functional groups such as -COO-, N-H, C=O, and C-O were involved in forming TBCPLMW-Ca. The particle size distributions and scanning electron microscopy results revealed that folding and aggregation of peptides were found in the chelate. Stability studies showed that TBCPLMW-Ca was relatively stable under thermal processing and more pronounced changes have been observed in simulated gastric digestion, presumably the acidic environment was the main factor causing the dissociation of the TBCPLMW-Ca. The results of this study provide a scientific basis for the preparation of a novel calcium supplement and is beneficial for comprehensive utilization of tuna bones.

Purification, Identification, Chelation Mechanism, and Calcium Absorption Activity of a Novel Calcium-Binding Peptide from Peanut (Arachis hypogaea) Protein Hydrolysate

A novel calcium-binding peptide was purified from peanut protein hydrolysate using gel filtration chromatography and identified using HPLC-MS/MS. Its amino acid sequence was determined as Phe-Pro-Pro-Asp-Val-Ala (FPPDVA, named as FA6) with the calcium-binding capacity of 15.67 ± 0.39 mg/g. Then, the calcium chelating characteristics of FPPDVA were investigated using ultraviolet-visible absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy, particle size, and zeta potential. The results showed that FPPDVA interacted with calcium ions, the chelation of calcium ions induced FPPDVA to fold and form a denser structure, the calcium-binding sites may mainly involve oxygen atoms from the carboxyl residues of Asp and Ala, and Phe possessed contact energy and carbonyl residues of Val. Microstructure analysis showed that FPPDVA-calcium chelate exhibited a regularly ordered and tightly aggregated sheets or block structures. Additionally, FPPDVA-calcium chelate had good gastrointestinal digestive stability and thermal stability. The results of everted rat intestinal sac and Caco-2 cell monolayer experiments showed that FPPDVA-calcium chelate could promote calcium absorption and transport through the Cav1.3 and TRPV6 calcium channels. These data suggest that FPPDVA-calcium chelate possesses the potential to be developed and applied as calcium supplement.

Process Optimization, Structural Characterization, and Calcium Release Rate Evaluation of Mung Bean Peptides-Calcium Chelate

To reduce grievous ecological environment pollution and protein resource waste during mung bean starch production, mung bean peptides-calcium chelate (MBP-Ca) was synthesized as a novel and efficient calcium supplement. Under the optimal conditions (pH = 6, temperature = 45 °C, mass ratio of mung bean peptides (MBP)/CaCl₂ = 4:1, MBP concentration = 20 mg/mL, time = 60 min), the obtained MBP-Ca achieved a calcium chelating rate of 86.26%. MBP-Ca, different from MBP, was a new compound rich in glutamic acid (32.74%) and aspartic acid (15.10%). Calcium ions could bind to MBP mainly through carboxyl oxygen, carbonyl oxygen, and amino nitrogen atoms to form MBP-Ca. Calcium ions-induced intra- and intermolecular interactions caused the folding and aggregation of MBP. After the chelation reaction between calcium ions and MBP, the percentage of β-sheet in the secondary structure of MBP increased by 1.90%, the size of the peptides increased by 124.42 nm, and the dense and smooth surface structure of MBP was transformed into fragmented and coarse blocks. Under different temperatures, pH, and gastrointestinal simulated digestion conditions, MBP-Ca exhibited an increased calcium release rate compared with the conventional calcium supplement CaCl₂. Overall, MBP-Ca showed promise as an alternative dietary calcium supplement with good calcium absorption and bioavailability.

The Formation, Structural Characteristics, Absorption Pathways and Bioavailability of Calcium–Peptide Chelates

Calcium is one of the most important mineral elements in the human body and is closely related to the maintenance of human health. To prevent calcium deficiency, various calcium supplements have been developed, but their application tends to be limited by low calcium content and highly irritating effects on the stomach, among other side effects. Recently, calcium–peptide chelates, which have excellent stability and are easily absorbed, have received attention as an alternative emerging calcium supplement. Calcium-binding peptides (CaBP) are usually obtained via the hydrolysis of animal or plant proteins, and calcium-binding capacity (CaBC) can be further improved through chromatographic purification techniques. In calcium ions, the phosphate group, carboxylic group and nitrogen atom in the peptide are the main binding sites, and the four modes of combination are the unidentate mode, bidentate mode, bridging mode and α mode. The stability and safety of calcium–peptide chelates are discussed in this paper, the intestinal absorption pathways of calcium elements and peptides are described, and the bioavailability of calcium–peptide chelates, both in vitro and in vivo, is also introduced. This review of the research status of calcium–peptide chelates aims to provide a reasonable theoretical basis for their application as calcium supplementation products.

A comprehensive review on preparation, structure-activities relationship, and calcium bioavailability of casein phosphopeptides

Calcium is one of the important elements for human health. Calcium deficiencies can lead to numerous diseases. Calcium chelating peptides have shown potential application in the management of calcium deficiencies. Casein phosphopeptides (CPP) are phosphoseryl-containing fragments of casein by enzymatic hydrolysis or fermentation during manufacture of milk products as well as during intestinal digestion. An increasing number of CPP with the ability to facilitate and enhance the bioavailability of calcium are being discovered and identified. In this review, 249 reported CPP derived from four types of bovine casein (αs1, αs2, β and κ) were collected, and the amino acid sequence and phosphoserine group information were sorted out. This review outlines the current enzyme hydrolysis, detection methods, purification, structure-activity relationship and mechanism of intestinal calcium absorption in vitro and in vivo as well as application of CPP.

Purification and Characterization of a Novel Calcium-Binding Heptapeptide from the Hydrolysate of Tilapia Bone with Its Osteogenic Activity

In this study, a calcium-binding peptide was obtained by hydrolyzing tilapia bone and its osteogenic activity was evaluated. Animal protease was selected from nine enzymes, and its hydrolysate was purified through preparative and semi-preparative reverse phase high-performance liquid chromatography. The purified peptide was identified as DGPSGPK (656.32 Da) and its calcium-binding capacity reached 111.98 µg/mg. The peptide calcium chelate (DGPSGPK-Ca) was obtained, and its structure was characterized through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and mass spectrometry (MS). The results of XRD and SEM showed that DGPSGPK-Ca was formed as a new compound. The carboxyl and amino groups of Lys and Asp residues may be the chelating sites of DGPSGPK according to the FTIR and MS results. The molecular simulation showed the carbonyl groups of Asp, Pro, Ser, and Lys residues involved in the binding of calcium. The interaction of DGPSGPK and different integrins was evaluated by molecular docking simulation, and the main forces involved were electrostatic interaction forces, hydrogen bonding and hydrophobic interactions. Furthermore, DGPSGPK could inhibit the differentiation of osteoclast and promote the proliferation, differentiation and mineralization of osteoblasts.

Mimicking the Composition and Structure of the Osteochondral Tissue to Fabricate a Heterogeneous Three-Layer Scaffold for the Repair of Osteochondral Defects

Heterogeneous three-layer scaffolds were fabricated by mimicking the biochemical composition and structure of the hyaline cartilage, calcified cartilage, and subchondral bone of the osteochondral tissue for the repair of osteochondral defects. The hyaline cartilage layer was composed of collagen I (50.0 wt %) and sodium hyaluronate (50.0 wt %). The calcified cartilage layer and subchondral bone layer were composed of collagen I, sodium hyaluronate, and nanohydroxyapatite with different proportions. N-Hydroxysuccinimide/N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride was used to mediate the crosslinking reaction of the amine groups of collagen with carboxyl groups of sodium hyaluronate. The hyaline cartilage layer and calcified cartilage layer were designed as dense structures, while the subchondral bone layer was designed as a relatively loose structure by adjusting the crosslinking degree. The scaffolds displayed a uniform and interconnected porous structure and possessed a high porosity over 85%, which were conducive to cellular adhesion and proliferation. The scaffolds could remain at 50-75% after 30 days of degradation owing to crosslinking, providing enough time for the regeneration of the osteochondral tissue. Especially, the hyaline cartilage layer and calcified cartilage layer preferred to induce the proliferation of chondrocytes, while the subchondral bone layer was more conducive to the proliferation of osteoblasts. In conclusion, the heterogeneous multilayer scaffolds could serve as implant materials for osteochondral reconstruction.

A comprehensive review of calcium and ferrous ions chelating peptides: Preparation, structure and transport pathways

Calcium and iron play crucial roles in human health, deficiencies of which have globally generated public health risks. The poor solubility, low bioavailability and gastrointestinal irritation of existing commercial mineral supplements limit their further application. As an emerging type of mineral supplement, mineral chelating peptides have drawn plenty of attention due to their advantages in stability, absorptivity and safety. A majority of calcium and ferrous ions chelating peptides have been isolated from food processing by-products. Enzymatic hydrolysis combined with affinity chromatography, gel filtration and other efficient separation techniques is the predominant method to obtain peptides with high calcium and ferrous affinity. Peptides with small molecular weight are more likely to chelate metals, and carboxyl, amino groups and nitrogen, oxygen, sulfur atoms in the side chain, which can provide lone-pair electrons to combine with metallic ions. Unidentate, bidentate, tridentate, bridging and α mode are regarded as common chelating modes. Moreover, the stability of peptide-mineral complexes in the gastrointestinal tract and possible transport pathways were summarized. This review is to present an overview of the latest research progress, existing problems and research prospects in the field of peptide-mineral complexes and to provide a more comprehensive theoretical basis for their exploitation in food industry.

Assembling cyanidin-3-O-glucoside by using low-viscosity alginate to improve its in vitro bioaccessibility and in vivo bioavailability

In this work, an enteric soluble alginate was proposed to improve the absorption efficiency of cyanidin-3-O-glucoside (C3G) through molecular self-assembly. Under the optimized conditions, the obtained low-viscosity alginate (LVA) was released completely during the simulated gastrointestinal digestion and an LVA-C3G complex with 84.2% binding efficiency was acquired. Fourier transform infrared spectroscopy displayed that the characteristic spectrum of C3G had disappeared after the LVA conjugation. Furthermore, based on the analysis of scanning electron microscopy and differential scanning calorimetry, a porous network structure and the shifted endothermic peak in the thermograms were observed, further confirming the formation of a complex between LVA and C3G. The results of simulated gastrointestinal digestion reveal that the LVA assembly significantly (p < 0.05) improved the bioaccessibility of C3G. Correspondingly, the C3G level in mouse plasma was increased by 27.4% in the C3G-LVA group. This suggests the suitability of LVA as an oral delivery vehicle for dietary anthocyanins.

Investigating the calcium binding characteristics of black bean protein hydrolysate

The black bean protein has been widely utilized to prepare hydrolysates with different bioactive properties. Herein, we hydrolyzed the black bean protein to prepare hydrolysate with calcium binding activity and characterized its behavior. Our results showed that ficin was superior in obtaining hydrolysate with calcium binding capacity in comparison with trypsin, alcalase and bromelain. In particular, the optimal capacity of ficin hydrolysate reached 77.54 ± 1.61 μg mg-1, where the optimal hydrolysis conditions of ficin were a temperature of 70 °C, a pH value of 6.2, an enzyme concentration of 1.61% and a time of 3 h. This might be due to high proportions of aspartic acid and glutamic acid (35.59%). Further spectral analysis evidenced the formation of hydrolysate-calcium complexes, demonstrating that the interaction between hydrolysate and calcium ions primarily occur on carboxyl oxygen atoms and amino nitrogen atoms. These findings provide a possible utilization of black bean hydrolysate to serve as a calcium supplement nutraceutical to enhance the absorption and bioavailability.

Peptide-Mineral Complexes: Understanding Their Chemical Interactions, Bioavailability, and Potential Application in Mitigating Micronutrient Deficiency

Iron, zinc, and calcium are essential micronutrients that play vital biological roles to maintain human health. Thus, their deficiencies are a public health concern worldwide. Mitigation of these deficiencies involves micronutrient fortification of staple foods, a strategy that can alter the physical and sensory properties of foods. Peptide-mineral complexes have been identified as promising alternatives for mineral-fortified functional foods or mineral supplements. This review outlines some of the methods used in the determination of the mineral chelating activities of food protein-derived peptides and the approaches for the preparation, purification and identification of mineral-binding peptides. The structure-activity relationship of mineral-binding peptides and the potential use of peptide-mineral complexes as functional food ingredients to mitigate micronutrient deficiency are discussed in relation to their chemical interactions, solubility, gastrointestinal digestion, absorption, and bioavailability. Finally, insights on the current challenges and future research directions in this area are provided.

Effect of Peptides from Alaska Pollock on Intestinal Mucosal Immunity Function and Purification of Active Fragments

The intestinal mucosal barrier plays an important role in systemic immune functions. This study aimed to find the mechanism of peptide from Alaska Pollock (APP) on intestinal mucosal immunity in mice induced by cyclophosphamide (Cy). Cy-induced decreases of body weight and index of immune organ were significantly improved by APP as compared with Cy group (p < 0.05). APP could promote the secretion of SIgA and IgA on intestinal mucosa (p < 0.05) and mainly had an impact on the final differentiation of IgA⁺ B cell, thereby promoting the secretion of plasma cells, which can be corroborated by the increases of IL-6 and IL-10 (p < 0.05). APP with high immune activity was separated and two peptides were purified and identified as Gly–Val–Ile–Lys and Ala–Cys–Asn–Gly–Arg. Therefore, APP can be considered as beneficial ingredients to protect the intestinal barrier disruption induced by Cy.

Remediation and Mechanisms of Cadmium Biosorption by a Cadmium-Binding Protein from Lentinula edodes

Cadmium bioremediation with metal-binding proteins is primarily conducted using metallothioneins (MTs). However, in the present study, we investigated a non-MT cadmium-binding protein from Lentinula edodes (LECBP) as a remediation tool for cadmium biosorption in Escherichia coli. The results indicated that the expression of LECBP significantly enhanced the cadmium biosorption capacity of transgenic E. coli. The secondary structure and conformation of LECBP were changed after binding with cadmium as evidenced by circular dichroism and fluorescence spectroscopy. The results of Fourier transform infrared spectroscopy indicated that carboxyl oxygen and amino nitrogen atoms were involved in the interaction between LECBP and cadmium. The results further demonstrated that glutamic acid and histidine residues are the potential binding sites. Our results have thus provided new insights into cadmium bioremediation in an aquatic environment.