Bioactivity of α-Lactalbumin Related to its Interaction with Fatty Acids: A Review

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.

Using the Relationship between Concentrations of Selected Whey Proteins and BHBA to Characterize the Metabolism of Dairy Cows in Early Lactation

Simple Summary

A negative energy balance alters the concentration of various fractions of cows’ milk. Moreover, key changes are observed in the fat and protein content. Therefore, by analyzing the concentration of individual proteins in milk, it is possible to indirectly monitor the health of the animal. Subclinical ruminal acidosis and ketosis are the primary economic issues in dairy farming due to non-specific symptoms, difficulty in obtaining a diagnosis and reduced milk production. The aim of the present study was to identify the relationship between the concentrations of blood β-hydroxybutyric (BHBA) and whey proteins in milk as a marker for the diagnosis of metabolic diseases. Whey proteins were significantly influenced by both the lactation phase and BHBA. Therefore, it can be concluded that whey proteins can be used as non-invasive markers for diagnosing metabolic diseases. A high concentration of β-lactoglobulin can be a marker for diagnosing ketosis. Conversely, elevated levels of α-lactalbumin may indicate the occurrence of a metabolic disorder, such as acidosis.

Abstract

A negative energy balance alters the concentration of various fractions of cows’ milk. Therefore, by analyzing the concentration of individual proteins in milk, it is possible to indirectly monitor the health of the animal. The aim of the present study was to identify the relationship between the concentrations of blood β-hydroxybutyric acid (BHBA) and whey proteins in milk as a marker for the diagnosis of metabolic diseases. The analysis included milk and blood samples from 95 Holstein-Friesian cows, which were divided into three groups that were differentiated in terms of serum BHBA levels 5–7 days post-calving: LBHBA, low level of BHBA: 0.200–0.500 mmol/L; NBHBA, optimal level of BHBA- control group: 0.500–1.200 mmol/L; HBHBA, high level of BHBA: >1.200 mmol/L. Concentrations of α-lactoalbumin in the milk after 7 days of lactation proceeded in accordance with the concentration of β-hydroxybutyric acid, as follows: LBHBA > NBHBA > HBHBA. Concentrations of β-lactoglobulin in milk after 14 days of lactation proceeded in accordance with the concentration of β-hydroxybutyric acid, as follows: LBHBA < NBHBA < HBHBA. Therefore, it can be concluded that whey proteins can be used as non-invasive markers for diagnosing metabolic diseases. A high concentration of β-lactoglobulin can be a marker for diagnosing ketosis. Conversely, elevated levels of α-lactalbumin may indicate the occurrence of a metabolic disorder, such as acidosis.

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.

DIA proteomics reveals hypotensive and immune-enhancing constituents in buffalo whey from different altitudes

The selection of raw milk with high levels of functional components that have health-promoting activities is very important for the exploitation and production of functional milk, but the differences in the functional components of whey from buffalo raised at different altitudes have not been thoroughly investigated. Here, we detected the effects of altitudes on the functional components in whey from dairy buffalo farms situated at low altitude (LA), medium altitude (MA), and high altitude (HA) sites with data-independent acquisition proteomic approaches. In 33 samples, 9331 peptides corresponding to 1008 high-confidence proteins were detected. HA-whey had a lower level of angiotensinogen than that of the LA- and MA-whey, and conversely contained higher levels of immune-enhancing components than for the latter two groups. Differential proteins were involved in vascular smooth muscle contraction, complement and coagulation cascades, and the secretion, production and regulation pathways in immune components. LA-whey showed higher levels of lymphocyte antigen and selenoprotein F than that of the HA-whey. Owing to the biological functions of their most abundant components, HA- and LA-whey are suitable for the processing of functional milk for lowering blood pressure, and the production of immune milk, respectively.

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.

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.

Bayesian Network Inference Enables Unbiased Phenotypic Anchoring of Transcriptomic Responses to Cigarette Smoke in Humans

Microarray-based transcriptomic analysis has been demonstrated to hold the opportunity to study the effects of human exposure to, e.g., chemical carcinogens at the whole genome level, thus yielding broad-ranging molecular information on possible carcinogenic effects. Since genes do not operate individually but rather through concerted interactions, analyzing and visualizing networks of genes should provide important mechanistic information, especially upon connecting them to functional parameters, such as those derived from measurements of biomarkers for exposure and carcinogenic risk. Conventional methods such as hierarchical clustering and correlation analyses are frequently used to address these complex interactions but are limited as they do not provide directional causal dependence relationships. Therefore, our aim was to apply Bayesian network inference with the purpose of phenotypic anchoring of modified gene expressions. We investigated a use case on transcriptomic responses to cigarette smoking in humans, in association with plasma cotinine levels as biomarkers of exposure and aromatic DNA-adducts in blood cells as biomarkers of carcinogenic risk. Many of the genes that appear in the Bayesian networks surrounding plasma cotinine, and to a lesser extent around aromatic DNA-adducts, hold biologically relevant functions in inducing severe adverse effects of smoking. In conclusion, this study shows that Bayesian network inference enables unbiased phenotypic anchoring of transcriptomics responses. Furthermore, in all inferred Bayesian networks several dependencies are found which point to known but also to new relationships between the expression of specific genes, cigarette smoke exposure, DNA damaging-effects, and smoking-related diseases, in particular associated with apoptosis, DNA repair, and tumor suppression, as well as with autoimmunity.

Bovine β-lactoglobulin/fatty acid complexes: binding, structural, and biological properties

Ligand-binding properties of β-lactoglobulin (β-lg) are well documented, but the subsequent biological functions are still unclear. Focusing on fatty acids/β-lg complexes, the structure-function relationships are reviewed in the light of the structural state of the protein (native versus non-native aggregated proteins). After a brief description of β-lg native structure, the review takes an interest in the binding properties of native β-lg (localization of binding sites, stoichiometry, and affinity) and the way the interaction affects the biological properties of the protein and the ligand. The binding properties of non-native aggregated forms of β-lg that are classically generated during industrial processing are also related. Structural changes modify the stoichiometry and the affinity of β-lg for fatty acids and consequently the biological functions of the complex. Finally, the fatty acid-binding properties of other whey proteins (α-lactalbumin, bovine serum albumin) and some biological properties of the complexes are also addressed. These proteins affect β-lg/fatty acids complex in whey given their competition with β-lg for fatty acids.

The transition from the native to the acid-state characterized by multi-spectroscopy approach: study for the holo-form of bovine α-lactalbumin

The transition of the holo-form of bovine α-lactalbumin from the native (N) to the pH-generated acidic-state (A-state) was analyzed by probing its tertiary and secondary structure using a concerted spectroscopic approach combining near- and far-UV circular dichroism (CD), electrospray ionization ion mobility mass spectrometry (ESI-IM-MS), vibrational circular dichroism (VCD), and Fourier transform infrared spectroscopy (FTIR) in the attenuated total reflection (ATR) and transmission (TR) modes. The spectroscopic results, which relied on the interaction of an electromagnetic field with different molecular targets, confirmed the decay of extensive rigid side-chain packing interactions during the pH-induced N→A-state transition and revealed the targets' dependence on secondary structural changes. Independent analyses of the spectral changes using two methods of multivariate analysis, such as principal component analysis and two-dimensional correlation spectroscopy, revealed small but significant differences in the secondary structure as a result of the all-or-none transition. The cooperativity of the transition was quantitatively described using values corresponding to the mid-point (tm) and width of the transition (Δtm). The averages of the two parameters, calculated using the data collected by the different probes, were equal to 3.5±0.2 and 0.6±0.1(SE), respectively. The variable two-state nature of the cooperative N→A-state transition confirmed that the protonation of the side chain carboxyl groups on the Asp and Glu residues and that the release of a Ca(2+) ion induced structural changes on both the secondary and tertiary levels. The changes have been confirmed by results obtained from the concerted spectroscopic approach.

An alternative method for cDNA cloning from surrogate eukaryotic cells transfected with the corresponding genomic DNA

cDNA is widely used in gene function elucidation and/or transgenics research but often suitable tissues or cells from which to isolate mRNA for reverse transcription are unavailable. Here, an alternative method for cDNA cloning is described and tested by cloning the cDNA of human LALBA (human alpha-lactalbumin) from genomic DNA. First, genomic DNA containing all of the coding exons was cloned from human peripheral blood and inserted into a eukaryotic expression vector. Next, by delivering the plasmids into either 293T or fibroblast cells, surrogate cells were constructed. Finally, the total RNA was extracted from the surrogate cells and cDNA was obtained by RT-PCR. The human LALBA cDNA that was obtained was compared with the corresponding mRNA published in GenBank. The comparison showed that the two sequences were identical. The novel method for cDNA cloning from surrogate eukaryotic cells described here uses well-established techniques that are feasible and simple to use. We anticipate that this alternative method will have widespread applications.