Caleosin-assembled oil bodies as a potential delivery nanocarrier

Artificial oil bodies: A review on composition, properties, biotechnological applications, and improvement methods

In order to simulate the structure of natural oil body, artificial oil bodies (AOBs) are fabricated by the integration of oleosins, triacylglycerols (TAGs) and phospholipids (PLs) in vitro. Recently, AOBs have gained great research interest both in the food and biological fields due to its ability to act as a novel delivery system for bioactive compounds and as a carrier for target proteins. This review aims to summarize the composition and the preparation methods of AOBs, examine the factors influencing their stability. Moreover, this contribution focusses on exploring the application of AOBs to encapsulate functional ingredients that are prone to oxidation as well as improve efficiency involved in protein purification, renaturation and immobilization by reducing the complex steps. In addition, the improvement measures to further enhance the stability and efficacy of AOBs are also discussed. The application of AOBs is expected to be a big step towards replacing existing bioreactors and delivery systems.

Caleosin/peroxygenases: multifunctional proteins in plants

BACKGROUND

Caleosin/peroxygenases (CLO/PXGs) are a family of multifunctional proteins that are ubiquitous in land plants and are also found in some fungi and green algae. CLO/PXGs were initially described as a class of plant lipid-associated proteins with some similarities to the oleosins that stabilize lipid droplets (LDs) in storage tissues, such as seeds. However, we now know that CLO/PXGs have more complex structures, distributions and functions than oleosins. Structurally, CLO/PXGs share conserved domains that confer specific biochemical features, and they have diverse localizations and functions.

SCOPE

This review surveys the structural properties of CLO/PXGs and their biochemical roles. In addition to their highly conserved structures, CLO/PXGs have peroxygenase activities and are involved in several aspects of oxylipin metabolism in plants. The enzymatic activities and the spatiotemporal expression of CLO/PXGs are described and linked with their wider involvement in plant physiology. Plant CLO/PXGs have many roles in both biotic and abiotic stress responses in plants and in their responses to environmental toxins. Finally, some intriguing developments in the biotechnological uses of CLO/PXGs are addressed.

CONCLUSIONS

It is now two decades since CLO/PXGs were first recognized as a new class of lipid-associated proteins and only 15 years since their additional enzymatic functions as a new class of peroxygenases were discovered. There are many interesting research questions that remain to be addressed in future physiological studies of plant CLO/PXGs and in their recently discovered roles in the sequestration and, possibly, detoxification of a wide variety of lipidic xenobiotics that can challenge plant welfare.

Characterization of lipid droplets from a Taxus media cell suspension and their potential involvement in trafficking and secretion of paclitaxel

Our paper describes the potential roles of lipid droplets of Taxus media cell suspension in the biosynthesis and secretion of paclitaxel and, therefore, highlights their involvement in improving its production. Paclitaxel (PTX) is a highly potent anticancer drug that is mainly produced using Taxus sp. cell suspension cultures. The main purpose of the current study is to characterize cellular LDs from T. media cell suspension with a particular focus on the biological connection of their associated proteins, the caleosins (CLOs), with the biosynthesis and secretion of PTX. A pure LD fraction obtained from T. media cells and characterized in terms of their proteome. Interestingly, the cellular LD in T. media sequester the PTX. This was confirmed in vitro, where about 96% of PTX (C⁰_PTX,_aq [mg L^-1]) in the aqueous solution was partitioned into the isolated LDs. Furthermore, silencing of CLO-encoding genes in the T. media cells led to a net decrease in the number and size of LDs. This coincided with a significant reduction in expression levels of TXS, DBAT and DBTNBT, key genes in the PTX biosynthesis pathway. Subsequently, the biosynthesis of PTX was declined in cell culture. In contrast, treatment of cells with 13-hydroperoxide C18:3, a substrate of the peroxygenase activity, induced the expression of CLOs, and, therefore, the accumulation of cellular LDs in the T. media cells cultures, thus increasing the PTX secretion. The accumulation of stable LDs is critically important for effective secretion of PTX. This is modulated by the expression of caleosins, a class of LD-associated proteins with a dual role conferring the structural stability of LDs as well as regulating lipidic bioactive metabolites via their enzymatic activity, thus enhancing the biosynthesis of PTX.

Effects of ultrasound-assisted salt (NaCl) extraction method on the structural and functional properties of Oleosin

²We propose a new ultrasound-assisted salt (NaCl) Oleosin extraction method, where the addition of NaCl induces the dissociation of Oleosin subunits and promotes the unfolding of the protein spatial structure. The yield of Oleosin post extraction and purification and solubility of Oleosin obtained using the proposed method were higher than those of Oleosin extracted using traditional methods, by 17.6% and 122.9%, respectively; reduction in particle size (to 52 nm) was also noted. Hydrogen bond dissociation, increase in surface hydrophobicity, and disulfide bond formation occurred simultaneously. However, the overall structure of Oleosin was not negatively affected. The physical properties of Oleosin, such as water and oil absorption, emulsification, and antioxidant activity, were improved, and the rate of Oleosin digestion decreased during the in vitro simulated digestion process. The proposed method provides a theoretical basis for producing proteins. This method can be utilized for effective extraction of Oleosin to achieve sustained release of the produced proteins.

Economic purification of recombinant uricase by artificial oil bodies

Rasburicase is an expensive treatment used to control hyperuricemia caused by tumour lysis syndrome (TLS). In this study, a non-chromatographic method was designed based on nano-oil bodies for convenient and economical purification of the recombinant uricase. For this purpose, two chimaeras were synthesized with a different arrangement of the uricase, caleosin and intein fragments. After confirming the protein expression by measuring the uricase activity at 293 nm, purification was conducted through oil-body construction. The results were resolved on the 12% SDS-PAGE gel. Finally, the stability of the oil bodies was examined against different salts, surfactants, temperatures, and pH values. According to our results, the overexpression of uricase-caleosin chimaera under the T7 promoter in Escherichia coli led to the production of soluble protein, which was successfully purified by artificial oil bodies. The active uricase was subsequently released through the self-splicing of intein. Further investigations highlighted the importance of the free C-terminus of caleosin in constructing artificial oil bodies. Moreover, surfactants and low temperature, in contrast to salts, improved the stability of oil bodies. In conclusion, caleosins are an efficient purification tag reducing the cost of purification compared to conventional chromatography methods.

Effects of covalent modification with epigallocatechin-3-gallate on oleosin structure and ability to stabilize artificial oil body emulsions

The purpose of this study was to enhance the stability and functional properties of artificial oil body (AOB) emulsions. Herein, we covalently conjugated oleosin (OL) and epigallocatechin-3-gallate (EGCG) under alkaline conditions to obtain OL-EGCG conjugates. The results revealed that the structural characteristics of OL are improved by covalent binding to EGCG, with the OL-EGCG yield maximized at an EGCG concentration of 150 μM. We prepared AOB emulsions using native OL, the OL-EGCG conjugates, phosphatidylcholine (PC), and soybean oil for embedding curcumin. The results show that the protein components and phospholipids are bound in the AOB emulsion by hydrogen bonding and hydrophobic interactions. The covalent OL-EGCG/PC-stabilized emulsions exhibited more uniform droplet distributions, stronger thermal stabilities, and higher curcumin retentions than the other samples. These results indicated that the OL-EGCG/PC complexes are potential stabilizers for AOB emulsions and provided fresh insight into preparing highly stable emulsion embedding systems with good encapsulation efficiencies.

Nature-Assembled Structures for Delivery of Bioactive Compounds and Their Potential in Functional Foods

Consumers are demanding more natural, healthy, and high-quality products. The addition of health-promoting substances, such as bioactive compounds, to foods can boost their therapeutic effect. However, the incorporation of bioactive substances into food products involves several technological challenges. They may have low solubility in water or poor stability in the food environment and/or during digestion, resulting in a loss of their therapeutic properties. Over recent years, the encapsulation of bioactive compounds into laboratory-engineered colloidal structures has been successful in overcoming some of these hurdles. However, several nature-assembled colloidal structures could be employed for this purpose and may offer many advantages over laboratory-engineered colloidal structures. For example, the casein micelles and milk fat globules from milk and the oil bodies from seeds were designed by nature to deliver biological material or for storage purposes. These biological functional properties make them good candidates for the encapsulation of bioactive compounds to aid in their addition into foods. This review discusses the structure and biological function of different nature-assembled carriers, preparation/isolation methods, some of the advantages and challenges in their use as bioactive compound delivery systems, and their behavior during digestion.

Affibody molecules for molecular imaging and targeted drug delivery in the management of breast cancer

Breast cancer is one of the leading reasons for the morbidity and mortality of cancer related death globally. The modern therapies are basically the combination of the breast-preserving surgeries or ablation with or without node biopsy or destroying the carcinoma cells adjuvant with chemotherapy, radiotherapy, hormonal or biological therapies depending upon the nature of the receptor of the cancerous cells, nature of the lymph node, as well as the tendency of the recurrence. For decade's carcinoma management suffered by the limitation of imagining, targeting and penetrability problem associated with management and cure of this deadly disease leads to unwanted chemo-toxicity and side effects. Alike other antibody mimetics, affibodies are designed with the combinatorial protein engineering approaches which are small and robust protein scaffolds retaining the favorable folding and stability. Affibody is one of the significantly important tools for imaging and diagnosis of the affinity specific over expressed proteins in the breast cancer management. The review summarizes the various affibody strategies uses in the management of breast cancer.

In vivo immobilization of D-hydantoinase in Escherichia coli

D-P-Hydroxyphenylglycine (D-HPG) is a precursor required for the synthesis of semi-synthetic antibiotics. This unnatural amino acid can be produced by a transformation reaction mediated by D-hydantoinase (D-HDT) and d-amidohydrolase. In this study, a method was developed to integrate production and immobilization of recombinant D-HDT in vivo. This was approached by first fusion of the gene encoding D-HDT with phaP (encoding phasin) of Ralstonia eutropha H16. The fusion gene was then expressed in the Escherichia coli strain that carried a heterologous synthetic pathway for polyhydroxyalkanoate (PHA). As a result, d-HDT was found to associate with isolated PHA granules. Further characterization illustrated that D-HDT immobilized on PHA exhibited the maximum activity at pH 9 and 60°C and had a half-life of 95 h at 40°C. Moreover, PHA-bound d-HDT could be reused for 8 times with the conversion yield exceeding 90%. Overall, it illustrates the feasibility of this approach to facilitate in vivo immobilization of enzymes in heterologous E. coli strain, which may open a new avenue of enzyme application in industry.

A useful method integrating production and immobilization of recombinant cellulase

The development of cellulase-based bioprocess is afflicted by the processing efficiency of enzymes. To address this issue, a method based on artificial oil bodies (AOBs) was proposed to integrate production and immobilization of recombinant cellulase. First, the heterologous endoglucanase (celA), cellobiohydrolase (celK), and β-glucosidase (gls) genes were individually fused with oleosin, a structural protein of plant seed oils. After expression in Escherichia coli, each fusion protein of insolubility was mixed together with plant oils. AOBs were assembled by subjecting the mixture to sonication. Consequently, active CelA, CelK, and Gls were resumed and co-immobilized on AOBs surface. Finally, the assembly condition (including the protein ratio) and the reaction condition were further optimized by response surface methodology. The resulting AOBs-bound cellulase remained stable for 4 cycles of cellulose-hydrolyzed reactions. Overall, the result shows a promise of this proposed approach for processing recombinant cellulase, which may provide a facile method to investigate optimum combination of cellulase components towards various cellulosic materials.

Computational identification and phylogenetic analysis of the oil-body structural proteins, oleosin and caleosin, in castor bean and flax

Oil bodies (OBs) are the intracellular particles derived from oilseeds. These OBs store lipids as a carbon resource, and have been exploited for a variety of industrial applications including biofuels. Oleosin and caleosin are the common OB structural proteins which are enabling biotechnological enhancement of oil content and OB-based pharmaceutical formations via stabilizing OBs. Although the draft whole genome sequence information for Ricinus communis L. (castor bean) and Linum usitatissimum L. (flax), important oil seed plants, is available in public database, OB-structural proteins in these plants are poorly indentified. Therefore, in this study, we performed a comprehensive bioinformatic analysis including analysis of the genome sequence, conserved domains and phylogenetic relationships to identify OB structural proteins in castor bean and flax genomes. Using comprehensive analysis, we have identified 6 and 15 OB-structural proteins from castor bean and flax, respectively. A complete overview of this gene family in castor bean and flax is presented, including the gene structures, phylogeny and conserved motifs, resulting in the presence of central hydrophobic regions with proline knot motif, providing an evolutionary proof that this central hydrophobic region had evolved from duplications in the primitive eukaryotes. In addition, expression analysis of L-oleosin and caleosin genes using quantitative real-time PCR demonstrated that seed contained their maximum expression, except that RcCLO-1 expressed maximum in cotyledon. Thus, our comparative genomics analysis of oleosin and caleosin genes and their putatively encoded proteins in two non-model plant species provides insights into the prospective usage of gene resources for improving OB-stability.