Protein-fatty acid complexes: biochemistry, biophysics and function

HAMLET in human milk is resistant to digestion and carries essential free long chain polyunsaturated fatty acids and oleic acid

The oleic acid/alpha-lactalbumin complex HAMLET (human alpha-lactalbumin made lethal to tumors) is cytotoxic to various cancerous cell lines and is assembled from alpha-lactalbumin (ALA) and free oleic acid (OA). HAMLET is also cytotoxic to normal immature intestinal cells. It remains unclear if HAMLET, experimentally assembled with OA and heat, can spontaneously assemble in frozen human milk over time. To approach this issue, we used a set of timed proteolytic experiments to evaluate the digestibility of HAMLET and native ALA. The purity of HAMLET in human milk was confirmed by ultra high performance liquid chromatography coupled to tandem mass spectrometry and western blot to resolve the ALA and OA components. Timed proteolytic experiments were used to identify HAMLET in whole milk samples. Structural characterization of HAMLET was performed by Fournier transformed infrared spectroscopy and indicated a transformation of secondary structure with increased alpha-helical character of ALA upon binding to OA.

Effect of whey protein derivatives on cell viability, cell migration and cell cycle phases in MCF-7 cells

Objective: This study aimed to obtain protein derivatives after treatment of whey proteins with hazelnut oil and olive oil and determined their effects on MCF-7 cells. Materials and Methods: Whey proteins obtained from 6% whey powder were treated with hazelnut oil (HO) and olive oil (OO) at a protein to lipid ratio of 1:10 at 60 ̊C for 120 minutes. The protein derivatives formed with whey protein and HO or OO were applied to MCF-7 cancer cells and healthy fibroblasts. The effects of protein derivatives on cell viability, apoptosis, reactive oxygen species (ROS) production, wound healing, cell cycle phase distribution and cell cycle related proteins Akt and p21(Waf1/Cip1) expressions were investigated. Results: Cell viability decreased significantly after 24 h of incubation with WP:OO. The percentage of apoptotic or necrotic cells varied between 5-10% and no statistically significant effect was observed. There was no statistically significant difference in ROS production and colony formation between controls and WP:HO or WP:OO groups. Treatment of cells with WP:OO for 24 h significantly decreased cell migration compared to the control group. G2/M phase was significantly suppressed in WP:OO group compared to the control group. WP:OO also increased the expression of p21(Waf1/Cip1) significantly when compared with the control group. Conclusion: Our results showed that whey protein derivatives applied to MCF-7 cells are cytotoxic and may be useful in breast cancer treatment.

Carboxyl Group-Modified Myoglobin Induces TNF-α-Mediated Apoptosis in Leukemia Cells

Previous studies have shown that chemical modification may increase the activity of proteins or confer novel activity to proteins. Some studies have indicated that myoglobin (Mb) is cytotoxic; however, the underlying mechanisms remain unclear. In this study, we investigated whether chemical modification of the carboxyl group by semicarbazide could promote the Mb cytotoxicity in human leukemia U937 cells and the underlying mechanism of semicarbazide-modified myoglobin (SEM-Mb)-induced U937 cell death. The semicarbazide-modified Mb (SEM-Mb) induced U937 cell apoptosis via the production of cleaved caspase-8 and t-Bid, while silencing of FADD abolished this effect. These findings suggest that SEM-Mb can induce U937 cell death by activating the death receptor-mediated pathway. The SEM-Mb inhibited miR-99a expression, leading to increased NOX4 mRNA and protein expression, which promoted SIRT3 degradation, and, in turn, induced ROS-mediated p38 MAPK phosphorylation. Activated p38 MAPK stimulated miR-29a-dependent tristetraprolin (TTP) mRNA decay. Downregulation of TTP slowed TNF-α mRNA turnover, thereby increasing TNF-α protein expression. The SEM-Mb-induced decrease in cell viability and TNF-α upregulation were alleviated by abrogating the NOX4/SIRT3/ROS/p38 MAPK axis or ectopic expression of TTP. Taken together, our results demonstrated that the NOX4/SIRT3/p38 MAPK/TTP axis induces TNF-α-mediated apoptosis in U937 cells following SEM-Mb treatment. A pathway regulating p38 MAPK-mediated TNF-α expression also explains the cytotoxicity of SEM-Mb in the human leukemia cell lines HL-60, THP-1, K562, Jurkat, and ABT-199-resistant U937. Furthermore, these findings suggest that the carboxyl group-modified Mb is a potential structural template for the generation of tumoricidal proteins.

Drug-loaded oleic-acid grafted mesoporous silica nanoparticles conjugated with α-lactalbumin resembling BAMLET-like anticancer agent with improved biocompatibility and therapeutic efficacy

Despite its prominent therapeutic efficacy, chemotherapy has raised serious concerns due to the severe adverse effects and multidrug resistance evoked, which propels the search for safe and green therapeutic agents. BAMLET (bovine α-lactalbumin made lethal against tumor cell) is a well-known protein-based anticancer agent of selective tumoricidal activity. Here, we prepared oleic acid-modified mesoporous silica nanoparticles (OA-MSNs) conjugated with bovine α-lactalbumin, a lipoprotein complex resembling BAMLET formed on the surface of MSNs (MSN-BAMLET) to load the anticancer drug of docetaxel (DTX). Compared to that of OA-MSNs/DTX, the obtained MSN-BAMLET/DTX with a sustained and pH-responsive drug release behaviors exhibited good biocompatibility and enhanced cytotoxic effect against cancer cells. Moreover, the presence of lipoprotein complex in MSN-BAMLET contributed to the improved dispersion of the composite in solution and the inhibitory effect on the migration of cancer cells. Furthermore, the adsorption profiles of protein corona on the obtained nanoparticles were analyzed. It was found that the marked low amount and abundance of plasma proteins were adsorbed on the α-lactalbumin coated siliceous composite demonstrated its long circulation property. Finally, in vivo study showed that MSN-BAMLET/DTX contributed to the effective cancer ablation and the prolonged survival. Therefore, the constructed MSN-BAMLET of the mesoregular structure and peculiar tumoricidal effect provides a manipulable nanoplatform as drug nanocarrier for therapeutic applications.

Dietary Linolenic Acid Increases Sensitizing and Eliciting Capacities of Cow's Milk Whey Proteins in BALB/c Mice

α-Lactalbumin (BLA) and β-lactoglobulin (BLG) are the major whey proteins causing allergic reactions. Polyunsaturated fatty acids (PUFAs) stand among the extrinsic factors of the food matrix that can bind BLA and BLG and change their bioactivities, but their contribution to change the allergenic properties of these proteins has not been investigated. Here, we aimed to determine how PUFAs influence BLA and BLG to sensitize and trigger allergic responses in BALB/c mice. First, tricine-SDS-PAGE and spectroscopic assays identified that α-linolenic acid (ALA, as a proof-of-concept model) can induce BLA and BLG to form cross-linked complexes and substantially modify their conformation. Then, BALB/c mice (n = 10/group) were orally sensitized and challenged with BLA and BLG or ALA-interacted BLA and BLG, respectively. Allergic reactions upon oral challenge were determined by measuring clinical allergic signs, specific antibodies, levels of type-1/2 cytokines, the status of mast cell activation, and percentage of cell populations (B and T cells) in different tissues (PP, MLN, and spleen). Overall, systemic allergic reaction was promoted in mice gavage with ALA-interacted BLA and BLG by disrupting the Th1/Th2 balance toward a Th2 immune response with the decreased number of Tregs. Enhanced induction of Th2-related cytokines, as well as serum-specific antibodies and mast cell activation, was also observed. In this study, we validated that ALA in the food matrix promoted both the sensitization and elicitation of allergic reactions in BALB/c mice.

Assessment of direct binding interaction between CD36 and its potential lipid ligands using a peptide mimic of the receptor labeled with a fluorophore

Cluster of differentiation 36 (CD36) is a cell-surface receptor that recognizes diverse substances. We have presented indirect evidence that a short segment of the receptor comprising amino acids 149-168 contains a site for binding of its lipid ligands (e.g., distinct fatty acids and aldehydes). However, experimental support for their direct interactions is yet to be achieved. For this, we devised a fluorescence intensity assay, where a synthetic peptide consisting of CD36 amino acids 149-168 labeled with fluorescein isothiocyanate (FITC-CD36_149-168) and its variant peptides were used as positive and negative probes, respectively. First, we obtained results indicating that 1-palmitoyl-2-(5-keto-6-octenedioyl)phosphatidylcholine (an established CD36 ligand) but not 1-palmitoyl-2-arachidonyl-phosphatidylcholine (a non-ligand of the receptor) bound in a saturable and specific manner to FITC-CD36_149-168. Strikingly, the assay allowed us to provide the first evidence supporting direct and specific binding between the CD36 segment and fatty aldehydes (e.g., Z-11-hexadecenal). However, this method failed to illustrate specific interactions of the segment with fatty acids, such as oleic acid. Nonetheless, our findings offer further insight into the biologically relevant ligands and the role of CD36. In addition, we suggest that this fluorescence-based technique provides a convenient means to evaluate protein (peptide)-lipid interactions.

Biodegradable Binary and Ternary Complexes from Renewable Raw Materials

The aim of this paper is to investigate the interactions between polysaccharides with different electrical charges (anionic and neutral starches) and proteins and fats in food ingredients. Another objective is to understand the mechanisms of these systems and the interdependence between their properties and intermolecular interactions. At present, there are not many studies on ternary blends composed of natural food polymers: polysaccharides of different electrical charge (anionic and neutral starches), proteins and lipids. Additionally, there are no reports concerning what type of interactions between polysaccharide, proteins and lipids exist simultaneously when the components are mixed in different orders. This paper intends to fill this gap. It also presents the application of natural biopolymers in the food and non-food industries.

Carboxyl group-modified α-lactalbumin induces TNF-α-mediated apoptosis in leukemia and breast cancer cells through the NOX4/p38 MAPK/PP2A axis

To clarify the mechanism of semicarbazide-modified α-lactalbumin (SEM-LA)-mediated cytotoxicity, we investigated its effect on human U937 leukemia cells and MCF-7 breast cancer cells in the current study. SEM-LA induced apoptosis in U937 cells, which showed increased NOX4 expression, procaspase-8 degradation, and t-Bid production. FADD depletion inhibited SEM-LA-elicited caspase-8 activation, t-Bid production, and cell death, indicating that SEM-LA activated death receptor-mediated apoptosis in U937 cells. SEM-LA stimulated Ca²⁺-mediated Akt activation, which in turn increased Sp1- and p300-mediated NOX4 transcription. The upregulation of NOX4 expression promoted ROS-mediated p38 MAPK phosphorylation, leading to protein phosphatase 2A (PP2A)-regulated tristetraprolin (TTP) degradation. Remarkably, TTP downregulation increased the stability of TNF-α mRNA, resulting in the upregulation of TNF-α protein expression. Abolishment of Ca²⁺-NOX4-ROS axis-mediated p38 MAPK activation attenuated SEM-LA-induced TNF-α upregulation and protected U937 cells from SEM-LA-mediated cytotoxicity. The restoration of TTP expression alleviated the effect of TNF-α upregulation and cell death induced by SEM-LA. Altogether, the data in this study demonstrate that SEM-LA activates TNF-α-mediated apoptosis in U937 cells through the NOX4/p38 MAPK/PP2A axis. We think that a similar pathway can also explain the death of MCF-7 human breast cancer cells after SEM-LA treatment.

Conformational changes in bovine α-lactalbumin and β-lactoglobulin evoked by interaction with C18 unsaturated fatty acids provide insights into increased allergic potential

Bovine α-lactalbumin (BLA) and β-lactoglobulin (BLG) are the most common and severe food allergens in milk and they can bind C18 unsaturated fatty acids (UFAs) and their bioactivities were changed. This study aims to determine the effects of C18 UFAs on the structures of BLA and BLG and their allergic properties, such as antigenicity and allergenicity. We reveal that C18 UFAs can efficiently promote the gradual unfolding of the structures of BLA and BLG and increase their hydrophobicity. Moreover, the IgG binding ability and the expression of IgG-dependent activation marker CD200R3 on basophils were remarkably promoted after C18 UFA treatment. Finally, we also observed that C18 UFAs can enhance the IgE binding ability and the degranulation capacity of human basophil KU812 cells (intracellular Ca2+, histamine, β-Hex, and IL-6). Collectively, these results suggested that C18 UFAs changed the structures of BLA and BLG, which contributed to their increased allergic potential.

Gastrointestinal Digestion of Food Proteins under the Effects of Released Bioactive Peptides on Digestive Health

The gastrointestinal tract represents a specialized interface between the organism and the external environment. Because of its direct contact with lumen substances, the modulation of digestive functions by dietary substances is supported by a growing body of evidence. Food-derived bioactive peptides have demonstrated a plethora of activities in the organism with increasing interest toward their impact over the digestive system and related physiological effects. This review updates the biological effects of food proteins, specifically milk and soybean proteins, associated to gastrointestinal health and highlights the study of digestion products and released peptides, the identification of the active form/s, and the evaluation of the mechanisms of action underlying their relationship with the digestive cells and receptors. The approach toward the modifications that food proteins and peptides undergo during gastrointestinal digestion and their bioavailability is a crucial step for current investigations on the field. The recent literature on the regulation of digestive functions by peptides has been mostly considered in terms of their influence on gastrointestinal motility and signaling, oxidative damage and inflammation, and malignant cellular proliferation. A final section regarding the actual challenges and future perspectives in this scientific topic is critically discussed.

α-Lactalbumin, Amazing Calcium-Binding Protein

α-Lactalbumin (α-LA) is a small (Mr 14,200), acidic (pI 4–5), Ca²⁺-binding protein. α-LA is a regulatory component of lactose synthase enzyme system functioning in the lactating mammary gland. The protein possesses a single strong Ca²⁺-binding site, which can also bind Mg²⁺, Mn²⁺, Na⁺, K⁺, and some other metal cations. It contains several distinct Zn²⁺-binding sites. Physical properties of α-LA strongly depend on the occupation of its metal binding sites by metal ions. In the absence of bound metal ions, α-LA is in the molten globule-like state. The binding of metal ions, and especially of Ca²⁺, increases stability of α-LA against the action of heat, various denaturing agents and proteases, while the binding of Zn²⁺ to the Ca²⁺-loaded protein decreases its stability and causes its aggregation. At pH 2, the protein is in the classical molten globule state. α-LA can associate with membranes at neutral or slightly acidic pH at physiological temperatures. Depending on external conditions, α-LA can form amyloid fibrils, amorphous aggregates, nanoparticles, and nanotubes. Some of these aggregated states of α-LA can be used in practical applications such as drug delivery to tissues and organs. α-LA and some of its fragments possess bactericidal and antiviral activities. Complexes of partially unfolded α-LA with oleic acid are cytotoxic to various tumor and bacterial cells. α-LA in the cytotoxic complexes plays a role of a delivery carrier of cytotoxic fatty acid molecules into tumor and bacterial cells across the cell membrane. Perhaps in the future the complexes of α-LA with oleic acid will be used for development of new anti-cancer drugs.

Bioactive Metabolites of Marine Origin Have Unusual Effects on Model Membrane Systems

Marine sponges and soft corals have yielded novel compounds with antineoplastic and antimicrobial activities. Their mechanisms of action are poorly understood, and in most cases, little relevant experimental evidence is available on this topic. In the present study, we investigated whether agelasine D (compound 1) and three agelasine analogs (compound 2–4) as well as malonganenone J (compound 5), affect the physical properties of a simple lipid model system, consisting of dioleoylphospahtidylcholine and dioleoylphosphatidylethanolamine. The data indicated that all the tested compounds increased stored curvature elastic stress, and therefore, tend to deform the bilayer which occurs without a reduction in the packing stress of the hexagonal phase. Furthermore, lower concentrations (1%) appear to have a more pronounced effect than higher ones (5–10%). For compounds 4 and 5, this effect is also reflected in phospholipid headgroup mobility assessed using ³¹P chemical shift anisotropy (CSA) values of the lamellar phases. Among the compounds tested, compound 4 stands out with respect to its effects on the membrane model systems, which matches its efficacy against a broad spectrum of pathogens. Future work that aims to increase the pharmacological usefulness of these compounds could benefit from taking into account the compound effects on the fluid lamellar phase at low concentrations.

Protein-lipid complexes: molecular structure, current scenarios and mechanisms of cytotoxicity

Some natural proteins can be complexed with oleic acid (OA) to form an active protein-lipid formulation that can induce tumor-selective apoptosis. The first explored protein was human milk α-lactalbumin (α-LA), called HAMLET when composed with OA in antitumor form. Several groups have prepared active protein-lipid complexes using a variety of approaches, all of which depend on target protein destabilization or direct OA-protein incubation to alter pH to acid or alkaline condition. In addition to performing vital roles in inflammatory processes and immune responses, fatty acids can disturb different metabolic pathways and cellular signals. Therefore, the tumoricidal action of these complexes is related to OA rather than the protein that keeps OA in solution and acts as a vehicle for transferring OA molecules to tumor cells. However, other studies have suggested that the antitumor efficacy of these complexes was exerted by both protein and OA together. The potential is not limited to the anti-tumor activity of protein-lipid complexes but extends to other functions such as bactericidal activity. The protein shell enhances the solubility and stability of the bound fatty acid. These protein-lipid complexes are promising candidates for fighting various cancer types and managing bacterial and viral infections.

Temperature, pH, and Molecular Packing Effects on the Penetration of Oleic Acid Monolayer by α-Lactalbumin

Recently, we reported on the interfacial behavior of mixed oleic acid (OA)-α-lactalbumin monolayer and its relevance in the formation of tumoricidal HAMLET (human α-lactalbumin made lethal to tumor cells)-like complex. This complex is probably formed in the gastrointestinal tract, but it has not been proved so far. The molecular base and the underlying physicochemical forces leading to such complexation remain to be known as well. There are also several other issues related with the complex stoichiometry that need to be fully explained. This study provides insight into the mechanism of temperature, pH, and physical state of monolayer-dependent binding of OA by the milk protein- apo-α-lactalbumin. Using the Langmuir and Langmuir-Blodgett approaches, we investigated the interactions between the OA monolayer and the apo-bovine α-lactalbumin (BLA III) at different pH, temperatures, and molecular packing. We found that the most favorable conditions for the formation of mixed OA-BLA III film are relevant to the gastric environment. The stabilization of OA-BLA III at the interface is associated with the conformational changes of protein in the presence of fatty acids induced by low pH and high temperature in the expanded monolayer. Our approach helps to understand the molecular mechanism of HAMLET/bovine α-lactalbumin made lethal to tumor cells formation in vivo.

Direct observation of alpha-lactalbumin, adsorption and incorporation into lipid membrane and formation of lipid/protein hybrid structures

The interaction between proteins and membranes is of great interest in biomedical and biotechnological research for its implication in many functional and dysfunctional processes. We present an experimental study on the interaction between model membranes and alpha-lactalbumin (α-La). α-La is widely studied for both its biological function and its anti-tumoral properties. We use advanced fluorescence microscopy and spectroscopy techniques to characterize α-La-membrane mechanisms of interaction and α-La-induced modifications of membranes when insertion of partially disordered regions of protein chains in the lipid bilayer is favored. Moreover, using fluorescence lifetime imaging, we are able to distinguish between protein adsorption and insertion in the membranes. Our results indicate that, upon addition of α-La to giant vesicles samples, protein is inserted into the lipid bilayer with rates that are concentration-dependent. The formation of heterogeneous hybrid protein-lipid co-aggregates, paralleled with protein conformational and structural changes, alters the membrane structure and morphology, leading to an increase in membrane fluidity.

A Protein Complex from Human Milk Enhances the Activity of Antibiotics and Drugs against Mycobacterium tuberculosis

Mycobacterium tuberculosis, the causative agent of human tuberculosis (TB), has surpassed HIV/AIDS as the leading cause of death from a single infectious agent. The increasing occurrence of drug-resistant strains has become a major challenge for health care systems and, in some cases, has rendered TB untreatable. However, the development of new TB drugs has been plagued with high failure rates and costs. Alternative strategies to increase the efficacy of current TB treatment regimens include host-directed therapies or agents that make M. tuberculosis more susceptible to existing TB drugs. In this study, we show that HAMLET, an α-lactalbumin-oleic acid complex derived from human milk, has bactericidal activity against M. tuberculosis HAMLET consists of a micellar oleic acid core surrounded by a shell of partially denatured α-lactalbumin molecules and unloads oleic acid into cells upon contact with lipid membranes. At sublethal concentrations, HAMLET potentiated a remarkably broad array of TB drugs and antibiotics against M. tuberculosis For example, the minimal inhibitory concentrations of rifampin, bedaquiline, delamanid, and clarithromycin were decreased by 8- to 16-fold. HAMLET also killed M. tuberculosis and enhanced the efficacy of TB drugs inside macrophages, a natural habitat of M. tuberculosis Previous studies showed that HAMLET is stable after oral delivery in mice and nontoxic in humans and that it is possible to package hydrophobic compounds in the oleic acid core of HAMLET to increase their solubility and metabolic stability. The potential of HAMLET and other liprotides as drug delivery and sensitization agents in TB chemotherapy is discussed here.

A biophysical study on the mechanism of interactions of DOX or PTX with α-lactalbumin as a delivery carrier

Doxorubicin and paclitaxel, two hydrophobic chemotherapeutic agents, are used in cancer therapies. Presence of hydrophobic patches and a flexible fold could probably make α-Lactalbumin a suitable carrier for hydrophobic drugs. In the present study, a variety of thermodynamic, spectroscopic, computational, and cellular techniques were applied to assess α-lactalbumin potential as a carrier for doxorubicin and paclitaxel. According to isothermal titration calorimetry data, the interaction between α-lactalbumin and doxorubicin or paclitaxel is spontaneous and the K (M^-1) value for the interaction of α-lactalbumin and paclitaxel is higher than that for doxorubicin. Differential scanning calorimetry and anisotropy results indicated formation of α-lactalbumin complexes with doxorubicin or paclitaxel. Furthermore, molecular docking and dynamic studies revealed that TRPs are not involved in α-Lac's interaction with Doxorubicin while TRP 60 interacts with paclitaxel. Based on Pace analysis to determine protein thermal stability, doxorubicin and paclitaxel induced higher and lower thermal stability in α-lactalbumin, respectively. Besides, fluorescence lifetime measurements reflected that the interaction between α-lactalbumin with doxorubicin or paclitaxel was of static nature. Therefore, the authors hypothesized that α-lactalbumin could serve as a carrier for doxorubicin and paclitaxel by reducing cytotoxicity and apoptosis which was demonstrated during our in vitro cell studies.

Divergent Anticancer Activity of Free and Formulated Camel Milk α-Lactalbumin

Alpha-lactalbumin (α-LA), a small milk calcium-binding globular protein, is known to possess noticeable anticancer activity, which is determined by the ability of this protein to form complexes with oleic acid (OA). To date, in addition to human and bovine α-LA, the ability to form such anti-tumor complexes with OA was described for goat and camel α-LA. Although the mechanisms of the anticancer activity of human and bovine α-LA are already well-studied, little is currently known about the anticancer action of this camel protein. The goal of this study was to fill this gap and to analyze the anticancer and pro-apoptotic activities of camel α-LA in its free form (α-cLA) and as an OA-containing complex (OA-α-cLA) using four human cancer cell lines, including Caco-2 colon cancer cells, PC-3 prostate cancer cells, HepG-2 hepatoma cells, and MCF-7 breast cancer cells as targets. The anti-tumor activities of OA-α-cLA and α-cLA were analyzed using MTT test, annexin/PI staining, cell cycle analysis, nuclear staining, and tyrosine kinase (TK) inhibition methods. We show here that the OA-α-cLA complex does not affect normal cells but has noticeable anti-cancer activity, especially against MCF-7 cells, thus boosting the anticancer activity of α-cLA and improving the selectivity of OA. The OA-α-cLA complex mediated cancer cell death via selective induction of apoptosis and cell-cycle arrest at lower IC₅₀ than that of free α-cLA by more than two folds. However, OA induced apoptosis at higher extent than OA-α-cLA and α-cLA. OA also caused unselective apoptosis-dependent cell death in both normal and cancer cells to a similar degree. The apoptosis and cell-cycle arresting effect of OA-α-cLA may be attributed to the TK inhibition activity of OA. Therefore, OA-α-cLA serves as efficient anticancer complex with two functional components, α-cLA and OA, possessing different activities. This study declared the effectiveness of OA-α-cLA complex as a promising entity with anticancer activity, and these formulated OA-camel protein complexes constitute an auspicious approach for cancer remedy, particularly for breast cancer.

Unsaturated Long-Chain Fatty Acids Are Preferred Ferritin Ligands That Enhance Iron Biomineralization

Ferritin is a ubiquitous nanocage protein, which can accommodate up to thousands of iron atoms inside its cavity. Aside from its iron storage function, a new role as a fatty acid binder has been proposed for this protein. The interaction of apo horse spleen ferritin (HoSF) with a variety of lipids has been here investigated through NMR spectroscopic ligand-based experiments, to provide new insights into the mechanism of ferritin-lipid interactions, and the link with iron mineralization. 1D ¹ H, diffusion (DOSY) and saturation-transfer difference (STD) NMR experiments provided evidence for a stronger interaction of ferritin with unsaturated fatty acids compared to saturated fatty acids, detergents, and bile acids. Mineralization assays showed that oleate c aused the most efficient increase in the initial rate of iron oxidation, and the highest formation of ferric species in HoSF. The comprehension of the factors inducing a faster biomineralization is an issue of the utmost importance, given the association of ferritin levels with metabolic syndromes, such as insulin resistance and diabetes, characterized by fatty acid concentration dysregulation. The human ferritin H-chain homopolymer (HuHF), featuring ferroxidase activity, was also tested for its fatty acid binding capabilities. Assays show that oleate can bind with high affinity to HuHF, without altering the reaction rates at the ferroxidase site.

Liprotides made of α-lactalbumin and cis fatty acids form core-shell and multi-layer structures with a common membrane-targeting mechanism

α-Lactalbumin (aLA) has been shown to form complexes with oleic acid (OA), which may target cancer cells. We recently showed that aLA and several other proteins all form protein-OA complexes called liprotides with a generic structure consisting of a micellar OA core surrounded by a shell of partially denatured protein. Here we report that a heat treatment and an alkaline treatment method both allow us to prepare liprotide complexes composed of aLA and a range of unsaturated fatty acids (FA), provided the FAs contain cis (but not trans) double bonds. All liprotides containing cis-FA form both small and large species, which all consist of partially denatured aLA, though the overall shape of the species differs. Small liprotides have a simple core-shell structure while the larger liprotides are multi-layered, i.e. they have an additional layer of both FA and aLA surrounding the outside of the core-shell structure. All liprotides can transfer their entire FA content to vesicles, releasing aLA as monomers and softening the lipid membrane. The more similar to OA, the more efficiently the different FAs induce hemolysis. We conclude that aLA can take up and transfer a wide variety of FA to membranes, provided they contain a cis-bond. This highlights liprotides as a general class of complexes where both protein and cis-FA component can be varied without departing from a generic (though sometimes multi-layered) core-shell structure.

Using THz Spectroscopy, Evolutionary Network Analysis Methods, and MD Simulation to Map the Evolution of Allosteric Communication Pathways in c-Type Lysozymes

It is now widely accepted that protein function is intimately tied with the navigation of energy landscapes. In this framework, a protein sequence is not described by a distinct structure but rather by an ensemble of conformations. And it is through this ensemble that evolution is able to modify a protein's function by altering its landscape. Hence, the evolution of protein functions involves selective pressures that adjust the sampling of the conformational states. In this work, we focus on elucidating the evolutionary pathway that shaped the function of individual proteins that make-up the mammalian c-type lysozyme subfamily. Using both experimental and computational methods, we map out specific intermolecular interactions that direct the sampling of conformational states and accordingly, also underlie shifts in the landscape that are directly connected with the formation of novel protein functions. By contrasting three representative proteins in the family we identify molecular mechanisms that are associated with the selectivity of enhanced antimicrobial properties and consequently, divergent protein function. Namely, we link the extent of localized fluctuations involving the loop separating helices A and B with shifts in the equilibrium of the ensemble of conformational states that mediate interdomain coupling and concurrently moderate substrate binding affinity. This work reveals unique insights into the molecular level mechanisms that promote the progression of interactions that connect the immune response to infection with the nutritional properties of lactation, while also providing a deeper understanding about how evolving energy landscapes may define present-day protein function.

Milk proteins, peptides, and oligosaccharides: effects against the 21st century disorders

Milk is the most complete food for mammals, as it supplies all the energy and nutrients needed for the proper growth and development of the neonate. Milk is a source of many bioactive components, which not only help meeting the nutritional requirements of the consumers, but also play a relevant role in preventing various disorders. Milk-derived proteins and peptides have the potential to act as coadjuvants in conventional therapies, addressing cardiovascular diseases, metabolic disorders, intestinal health, and chemopreventive properties. In addition to being a source of proteins and peptides, milk contains complex oligosaccharides that possess important functions related to the newborn's development and health. Some of the health benefits attributed to milk oligosaccharides include prebiotic probifidogenic effects, antiadherence of pathogenic bacteria, and immunomodulation. This review focuses on recent findings demonstrating the biological activities of milk peptides, proteins, and oligosaccharides towards the prevention of diseases of the 21st century. Processing challenges hindering large-scale production and commercialization of those bioactive compounds have been also addressed.

Treatment with oleic acid reduces IgE binding to peanut and cashew allergens

Oleic acid (OA) is known to bind and change the bioactivities of proteins, such as α-lactalbumin and β-lactoglobulin in vitro. The objective of this study was to determine if OA binds to allergens from a peanut extract or cashew allergen and changes their allergenic properties. Peanut extract or cashew allergen (Ana o 2) was treated with or without 5mM sodium oleate at 70°C for 60 min (T1) or under the same conditions with an additional overnight incubation at 37°C (T2). After treatment, the samples were dialyzed and analyzed by SDS-PAGE and for OA content. IgE binding was evaluated by ELISA and western blot, using a pooled serum or plasma from individuals with peanut or cashew allergies. Results showed that OA at a concentration of 5mM reduced IgE binding to the allergens. Peanut sample T2 exhibited a lower IgE binding and a higher OA content (protein-bound) than T1. Cashew allergen T2 also showed a reduction in IgE binding. We conclude that OA reduces the allergenic properties of peanut extract and cashew allergen by binding to the allergens. Our findings indicate that OA in the form of sodium oleate may be potentially useful as a coating to reduce the allergenic properties of peanut and cashew allergens.

Generic structures of cytotoxic liprotides: nano-sized complexes with oleic acid cores and shells of disordered proteins

The cytotoxic complex formed between α-lactalbumin and oleic acid (OA) has inspired many studies on protein-fatty acid complexes, but structural insight remains sparse. After having used small-angle X-ray scattering (SAXS) to obtain structural information, we present a new, generic structural model of cytotoxic protein-oleic acid complexes, which we have termed liprotides (lipids and partially denatured proteins). Twelve liprotides formed from seven structurally unrelated proteins and prepared by different procedures all displayed core-shell structures, each with a micellar OA core and a shell consisting of flexible, partially unfolded protein, which stabilizes the OA micelle. The common structure explains similar effects exerted on cells by different liprotides and is consistent with a cargo off-loading of the OA into cell membranes.

Polyamidoamine dendrimer and oleic acid-functionalized graphene as biocompatible and efficient gene delivery vectors

Functionalized graphene has good potential in biomedical applications. To address a better and multiplex design of graphene-based gene vectors, the graphene-oleate-polyamidoamine (PAMAM) dendrimer hybrids were synthesized by the oleic acid adsorption and covalent linkage of PAMAM dendrimers. The micromorphology, electrical charge property, and amount of free amine groups of the graphene-oleate-PAMAM hybrids were characterized, and the peripheral functional groups were identified. The PAMAM dendrimers could be tethered onto graphene surface in high density. The graphene-oleate-PAMAM hybrids exhibit relatively good dispersity and stability in aqueous solutions. To evaluate the potential application of the hybrids in gene delivery vectors, cytotoxicity to HeLa and MG-63 cells and gene (plasmid DNA of enhanced green fluorescent protein) transfection capacity of the hybrids were investigated in detail. The graphene-oleate-PAMAM hybrids show mammalian cell type- and dose-dependent in vitro cytotoxicity. Under the optimal condition, the hybrids possess good biocompatibility and gene transfection capacity. The surface modification of graphene with oleic acid and PAMAM improves the gene transfection efficiency 13 times in contrast to the ultrasonicated graphene. Moreover, the hybrids show better transfection efficiency than the graphene oxide-PAMAM without the oleic acid modification.

A complex of equine lysozyme and oleic acid with bactericidal activity against Streptococcus pneumoniae

HAMLET and ELOA are complexes consisting of oleic acid and two homologous, yet functionally different, proteins with cytotoxic activities against mammalian cells, with HAMLET showing higher tumor cells specificity, possibly due to the difference in propensity for oleic acid binding, as HAMLET binds 5-8 oleic acid molecules per protein molecule and ELOA binds 11-48 oleic acids. HAMLET has been shown to possess bactericidal activity against a number of bacterial species, particularly those with a respiratory tropism, with Streptococcus pneumoniae displaying the greatest degree of sensitivity. We show here that ELOA also displays bactericidal activity against pneumococci, which at lower concentrations shows mechanistic similarities to HAMLET’s bactericidal activity. ELOA binds to S. pneumoniae and causes perturbations of the plasma membrane, including depolarization and subsequent rupture, and activates an influx of calcium into the cells. Selective inhibition of calcium channels and sodium/calcium exchange activity significantly diminished ELOA’s bactericidal activity, similar to what we have observed with HAMLET. Finally, ELOA-induced death was also accompanied by DNA fragmentation into high molecular weight fragments – an apoptosis-like morphological phenotype that is seen during HAMLET-induced death. Thus, in contrast to different mechanisms of eukaryote cell death induced by ELOA and HAMLET, these complexes are characterized by rather similar activities towards bacteria. Although the majority of these events could be mimicked using oleic acid alone, the concentrations of oleic acid required were significantly higher than those present in the ELOA complex, and for some assays, the results were not identical between oleic acid alone and the ELOA complex. This indicates that the lipid, as a common denominator in both complexes, is an important component for the complexes’ bactericidal activities, while the proteins are required both to solubilize and/or present the lipid at the bacterial membrane and likely to confer other and separate functions during the bacterial death.

Structural characterization of more potent alternatives to HAMLET, a tumoricidal complex of α-lactalbumin and oleic acid

HAMLET is a complex of human α-lactalbumin (hLA) with oleic acid (OA) that kills various tumor cells and strains of Streptococcus pneumoniae. More potent protein-OA complexes were previously reported for bovine α-lactalbumin (bLA) and β-lactoglobulin (bLG), and pike parvalbumin (pPA), and here we explore their structural features. The concentration dependencies of the tryptophan fluorescence of hLA, bLA, and bLG complexes with OA reveal their disintegration at protein concentrations below the micromolar level. Chemical cross-linking experiments provide evidence that association with OA shifts the distribution of oligomeric forms of hLA, bLA, bLG, and pPA toward higher-order oligomers. This effect is confirmed for bLA and bLG using the dynamic light scattering method, while pPA is shown to associate with OA vesicles. Like hLA binding, OA binding increases the affinity of bLG for small unilamellar dipalmitoylphosphatidylcholine vesicles, while pPA efficiently binds to the vesicles irrespective of OA binding. The association of OA with bLG and pPA increases their α-helix and cross-β-sheet content and resistance to enzymatic proteolysis, which is indicative of OA-induced protein structuring. The lack of excess heat sorption during melting of bLG and pPA in complex with OA and the presence of a cooperative thermal transition at the level of their secondary structure suggest that the OA-bound forms of bLG and pPA lack a fixed tertiary structure but exhibit a continuous thermal transition. Overall, despite marked differences, the HAMLET-like complexes that were studied exhibit a common feature: a tendency toward protein oligomerization. Because OA-induced oligomerization has been reported for other proteins, this phenomenon is inherent to many proteins.

Taurine supplementation of plant derived protein and n-3 fatty acids are critical for optimal growth and development of cobia, Rachycentron canadum

We examined growth performance and the lipid content in juvenile cobia, Rachycentron canadum, fed a taurine supplemented (1.5 %), plant protein based diet with two fish oil replacements. The first fish oil replacement was a thraustochytrid meal (TM + SOY) plus soybean oil (~9 % CL) and the second was a canola oil supplemented with the essential fatty acids (EFA) docosahexaenoic acid (DHA) and arachidonic acid (ARA) (~8 % CL). The diet using the thraustochytrid meal plus soybean oil performed equivalently to the fish oil diet; both resulting in significantly higher growth rates, lower feed conversion ratios, and higher survival than the supplemented canola oil diet, even though all three diets were similar in overall energy and met known protein and lipid requirements for cobia. The poor performance of the canola oil diet was attributed to insufficient addition of EFA in the supplemented canola oil source. Increasing levels of EFA in the supplemented canola oil above 0.5 g EFA kg(-1) would likely improve results with cobia. When fish fed either of the fish oil replacement diets were switched to the fish oil control diet, fatty acid profiles of the fillets were observed to transition toward that of the fish oil diet and could be predicted based on a standard dilution model. Based on these findings, a formulated diet for cobia can be produced without fish products providing 100 % survivorship, specific growth rates greater than 2.45 and feed conversion ratios less than 1.5, as long as taurine is added and EFA levels are above 0.5 g EFA kg(-1).