Can misfolded proteins be beneficial? The HAMLET case

Inhibitory Effects of Six Types of Tea on Aging and High-Fat Diet-Related Amyloid Formation Activities

Aging and lipid metabolism disorders promote the formation and accumulation of amyloid with β-sheet structure, closely related to cardiovascular disease, senile dementia, type 2 diabetes, and other senile degenerative diseases. In this study, five representative teas were selected from each of the six types of tea, and a total of 30 teas were selected to evaluate the inhibitory activities on the formation of aging-related amyloid in vitro. The results showed that the 30 teas had a significant inhibitory effect on the formation activity on aging-related amyloid at the protein level in vitro. Although the content of catechins is relatively low, black tea and dark tea still have significant antioxidant activity and inhibit the formation of amyloid. A high-fat diet established the model of lipid metabolism disorder in premature aging SAMP8 mice, and these mice were gavaged different tea water extracts. The results showed that different tea types have a significant inhibitory effect on the formation of β-amyloid and Aβ42 mediated by age-related lipid metabolism disorders, and the in vivo activity of fully fermented teas was better than that of green tea. The action mechanism was related to antioxidation, anti-inflammatory, and improving lipid metabolism.

Fish lysozyme gene family evolution and divergent function in early development

Lysozymes are an ancient group of antimicrobial enzymes of the innate immune system. Here we provide a comparative analysis of the evolution and function of lysozymes during early development in fish, the most speciose vertebrate group. In fishes, lineage and species-specific evolution of both C-type (chicken or conventional) and G-type (goose type) genes occurred. Phylogenetic analysis revealed that the teleost lysozyme G-type members group with the tetrapod homologues but the teleost C-type form three different clusters with the tetrapods. Most of the teleost C-type cluster with tetrapod Lyz but there are some that group with the mammalian Lyzl1/2 and LALBA. This suggests that early in gnathostome evolution these genes already existed and that lyzl1/2 and lalba genes are present in fish and tetrapods. Gene synteny analysis to confirm sequence orthologies failed to identify conserved genome regions between teleosts and other vertebrates lysozyme gene regions suggesting that in the ancestral bony fish genome lyz, lyzl1/2, lalba and lyg precursor genes were transposed to different chromosome regions. The homologue of the mammalian lactalbumin (LALBA) gene was identified for the first time in teleosts and was expressed in skin and during egg and larval development. Lysozyme activity was detected in teleost eggs and varied between species and in the gilthead sea bream lyg and lalba transcript abundance differed in eggs and larvae from different brood stock suggesting differences exist in maternal innate immune protection.

Concentration dependent effect of ethylene glycol on the structure and stability of holo α-lactalbumin: Characterization of intermediate state amidst soft interactions

The interior of the cell is crowded with different kinds of biological molecules with varying sizes, shapes and compositions which may affect physiological processes especially protein folding, protein conformation and protein stability. To understand the consequences of such a crowded environment, pH-induced unfolding of holo alpha-lactalbumin (holo α-LA) was studied in the presence of ethylene glycol (EG). The effect of EG on the folding and stability of holo α-LA in aqueous solution was investigated using several spectroscopic techniques. The results indicate that stabilization/destabilization of holo α-LA by EG is concentration- and pH-dependent. Low concentration of EG stabilizes the protein at pH near its pI. From the results of far-UV CD, UV-visible and ANS fluorescence, intermediate state (MG state) was characterized in the presence of high concentration of ethylene glycol. The results invoke a new mechanism for the formation of MG state identical to active component of BAMLET. MG state of holo α-LA has a direct implication to cancer therapy. MG state of α-LA in complex with specific type of lipid is a novel class of protein-based anti-cancer complexes that incorporate oleic acid and deliver it to the cancer cells.

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.

The Use of Human, Bovine, and Camel Milk Albumins in Anticancer Complexes with Oleic Acid

Oleic acid (OA) is a monounsaturated fatty acid that upon binding to milk proteins, such as α-lactalbumin and lactoferrin, forms potent complexes, which exert selective anti-tumor activity against malignant cells but are nontoxic for healthy normal cells. We showed that the interaction of OA with albumins isolated from human, bovine, and camel milk results in the formation of complexes with high antitumor activity against Caco-2, HepG-2, PC-3, and MCF-7 tumor cells. The antitumor effect of the complexes is mostly due to the action of oleic acid, similar to the case of OA complexes with other proteins. Viability of tumor cells is inhibited by the albumin-OA complexes in a dose dependent manner, as evaluated by the MTT assay. Strong induction of apoptosis in tumor cells after their treatment with the complexes was monitored by flow cytometry, cell cycle analysis, nuclear staining, and DNA fragmentation methods. The complex of camel albumin with OA displayed the most pronounced anti-tumor effects in comparison with the complexes of OA with human and bovine albumins. Therefore, these results suggest that albumins have the potential to be used as efficient and low cost means of tumor treatment.

Growth-incompetent monomers of human calcitonin lead to a noncanonical direct relationship between peptide concentration and aggregation lag time

The role of the peptide hormone calcitonin in skeletal protection has led to its use as a therapeutic for osteoporosis. However, calcitonin aggregation into amyloid fibrils limits its therapeutic efficacy, necessitating a modification of calcitonin's aggregation kinetics. Here, we report a direct relationship between human calcitonin (hCT) concentration and aggregation lag time. This kinetic trend was contrary to the conventional understanding of amyloid aggregation and persisted over a range of aggregation conditions, as confirmed by thioflavin-T kinetics assays, CD spectroscopy, and transmission EM. Dynamic light scattering, 1H NMR experiments, and seeded thioflavin-T assay results indicated that differences in initial peptide species contribute to this trend more than variations in the primary nucleus formation rate. On the basis of kinetics modeling results, we propose a mechanism whereby a structural conversion of hCT monomers is needed before incorporation into the fibril. Our kinetic mechanism recapitulates the experimentally observed relationship between peptide concentration and lag time and represents a novel mechanism in amyloid aggregation. Interestingly, hCT at low pH and salmon calcitonin (sCT) exhibited the canonical inverse relationship between concentration and lag time. Comparative studies of hCT and sCT with molecular dynamics simulations and CD indicated an increased α-helical structure in sCT and low-pH hCT monomers compared with neutral-pH hCT, suggesting that α-helical monomers represent a growth-competent species, whereas unstructured random coil monomers represent a growth-incompetent species. Our finding that initial monomer concentration is positively correlated with lag time in hCT aggregation could help inform future efforts for improving therapeutic applications of CT.

Antivirals against animal viruses

Antivirals are compounds used since the 1960s that can interfere with viral development. Some of these antivirals can be isolated from a variety of sources, such as animals, plants, bacteria or fungi, while others must be obtained by chemical synthesis, either designed or random. Antivirals display a variety of mechanisms of action, and while some of them enhance the animal immune system, others block a specific enzyme or a particular step in the viral replication cycle. As viruses are mandatory intracellular parasites that use the host's cellular machinery to survive and multiply, it is essential that antivirals do not harm the host. In addition, viruses are continually developing new antiviral resistant strains, due to their high mutation rate, which makes it mandatory to continually search for, or develop, new antiviral compounds. This review describes natural and synthetic antivirals in chronological order, with an emphasis on natural compounds, even when their mechanisms of action are not completely understood, that could serve as the basis for future development of novel and/or complementary antiviral treatments.

Protein-dependent Membrane Interaction of A Partially Disordered Protein Complex with Oleic Acid: Implications for Cancer Lipidomics

Bovine α-lactalbumin (BLA) forms cytotoxic complexes with oleic acid (OA) that perturbs tumor cell membranes, but molecular determinants of these membrane-interactions remain poorly understood. Here, we aim to obtain molecular insights into the interaction of BLA/BLA-OA complex with model membranes. We characterized the folding state of BLA-OA complex using tryptophan fluorescence and resolved residue-specific interactions of BLA with OA using molecular dynamics simulation. We integrated membrane-binding data using a voltage-sensitive probe and molecular dynamics (MD) to demonstrate the preferential interaction of the BLA-OA complex with negatively charged membranes. We identified amino acid residues of BLA and BLA-OA complex as determinants of these membrane interactions using MD, functionally corroborated by uptake of the corresponding α-LA peptides across tumor cell membranes. The results suggest that the α-LA component of these cytotoxic complexes confers specificity for tumor cell membranes through protein interactions that are maintained even in the lipid complex, in the presence of OA.

Prevention and treatment of colon cancer by peroral administration of HAMLET (human α-lactalbumin made lethal to tumour cells)

BACKGROUND

Most colon cancers start with dysregulated Wnt/β-catenin signalling and remain a major therapeutic challenge. Examining whether HAMLET (human α-lactalbumin made lethal to tumour cells) may be used for colon cancer treatment is logical, based on the properties of the complex and its biological context.

OBJECTIVE

To investigate if HAMLET can be used for colon cancer treatment and prevention. Apc(Min)(/+) mice, which carry mutations relevant to hereditary and sporadic human colorectal tumours, were used as a model for human disease.

METHOD

HAMLET was given perorally in therapeutic and prophylactic regimens. Tumour burden and animal survival of HAMLET-treated and sham-fed mice were compared. Tissue analysis focused on Wnt/β-catenin signalling, proliferation markers and gene expression, using microarrays, immunoblotting, immunohistochemistry and ELISA. Confocal microscopy, reporter assay, immunoprecipitation, immunoblotting, ion flux assays and holographic imaging were used to determine effects on colon cancer cells.

RESULTS

Peroral HAMLET administration reduced tumour progression and mortality in Apc(Min)(/+) mice. HAMLET accumulated specifically in tumour tissue, reduced β-catenin and related tumour markers. Gene expression analysis detected inhibition of Wnt signalling and a shift to a more differentiated phenotype. In colon cancer cells with APC mutations, HAMLET altered β-catenin integrity and localisation through an ion channel-dependent pathway, defining a new mechanism for controlling β-catenin signalling. Remarkably, supplying HAMLET to the drinking water from the time of weaning also significantly prevented tumour development.

CONCLUSIONS

These data identify HAMLET as a new, peroral agent for colon cancer prevention and treatment, especially needed in people carrying APC mutations, where colon cancer remains a leading cause of death.

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.

Lipids as tumoricidal components of human α-lactalbumin made lethal to tumor cells (HAMLET): unique and shared effects on signaling and death

Long-chain fatty acids are internalized by receptor-mediated mechanisms or receptor-independent diffusion across cytoplasmic membranes and are utilized as nutrients, building blocks, and signaling intermediates. Here we describe how the association of long-chain fatty acids to a partially unfolded, extracellular protein can alter the presentation to target cells and cellular effects. HAMLET (human α-lactalbumin made lethal to tumor cells) is a tumoricidal complex of partially unfolded α-lactalbumin and oleic acid (OA). As OA lacks independent tumoricidal activity at concentrations equimolar to HAMLET, the contribution of the lipid has been debated. We show by natural abundance (13)C NMR that the lipid in HAMLET is deprotonated and by chromatography that oleate rather than oleic acid is the relevant HAMLET constituent. Compared with HAMLET, oleate (175 μm) showed weak effects on ion fluxes and gene expression. Unlike HAMLET, which causes metabolic paralysis, fatty acid metabolites were less strongly altered. The functional overlap increased with higher oleate concentrations (500 μm). Cellular responses to OA were weak or absent, suggesting that deprotonation favors cellular interactions of fatty acids. Fatty acids may thus exert some of their essential effects on host cells when in the deprotonated state and when presented in the context of a partially unfolded protein.

Alternatively folded proteins with unexpected beneficial functions

HAMLET (human α-lactalbumin made lethal to tumour cells) and its related partially unfolded protein-fatty acid complexes are novel biomolecular nanoparticles that possess relatively selective cytotoxic activities towards tumour cells. One of the key characteristics is the requirement for the protein to be partially unfolded, hence endowing native proteins with additional functions in the alternatively folded states. Beginning with the history of its discovery and development, the cellular targets that appear to be strongly correlated with tumour cell death are introduced in the present article.

HAMLET: functional properties and therapeutic potential

Human α-lactalbumin made lethal to tumor cells (HAMLET) is the first member in a new family of protein–lipid complexes that kills tumor cells with high selectivity. The protein component of HAMLET is α-lactalbumin, which in its native state acts as a substrate specifier in the lactose synthase complex, thereby defining a function essential for the survival of lactating mammals. In addition, α-lactalbumin acquires tumoricidal activity after partial unfolding and binding to oleic acid. The lipid cofactor serves the dual role as a stabilizer of the altered fold of the protein and a coactivator of specific steps in tumor cell death. HAMLET is broadly tumoricidal, suggesting that the complex identifies conserved death pathways suitable for targeting by novel therapies. Sensitivity to HAMLET is defined by oncogene expression including Ras and c-Myc and by glycolytic enzymes. Cellular targets are located in the cytoplasmic membrane, cytoskeleton, mitochondria, proteasomes, lysosomes and nuclei, and specific signaling pathways are rapidly activated, first by interactions of HAMLET with the cell membrane and subsequently after HAMLET internalization. Therapeutic effects of HAMLET have been demonstrated in human skin papillomas and bladder cancers, and HAMLET limits the progression of human glioblastomas, with no evidence of toxicity for normal brain or bladder tissue. These findings open up new avenues for cancer therapy and the understanding of conserved death responses in tumor cells.

Electrostatic interactions play an essential role in the binding of oleic acid with α-lactalbumin in the HAMLET-like complex: a study using charge-specific chemical modifications

Human α-lactalbumin made lethal to tumor cells (HAMLET) and its analogs are partially unfolded protein-oleic acid (OA) complexes that exhibit selective tumoricidal activity normally absent in the native protein itself. To understand the nature of the interaction between protein and OA moieties, charge-specific chemical modifications of lysine side chains involving citraconylation, acetylation, and guanidination were employed and the biophysical and biological properties were probed. Upon converting the original positively-charged lysine residues to negatively-charged citraconyl or neutral acetyl groups, the binding of OA to protein was eliminated, as were any cytotoxic activities towards osteosarcoma cells. Retention of the positive charges by converting lysine residues to homoarginine groups (guanidination); however, yielded unchanged binding of OA to protein and identical tumoricidal activity to that displayed by the wild-type α-lactalbumin-oleic acid complex. With the addition of OA, the wild-type and guanidinated α-lactalbumin proteins underwent substantial conformational changes, such as partial unfolding, loss of tertiary structure, but retention of secondary structure. In contrast, no significant conformational changes were observed in the citraconylated and acetylated α-lactalbumins, most likely because of the absence of OA binding. These results suggest that electrostatic interactions between the positively-charged basic groups on α-lactalbumin and the negatively-charged carboxylate groups on OA molecules play an essential role in the binding of OA to α-lactalbumin and that these interactions appear to be as important as hydrophobic interactions.

Evolution of the mammalian lysozyme gene family

BACKGROUND

Lysozyme c (chicken-type lysozyme) has an important role in host defense, and has been extensively studied as a model in molecular biology, enzymology, protein chemistry, and crystallography. Traditionally, lysozyme c has been considered to be part of a small family that includes genes for two other proteins, lactalbumin, which is found only in mammals, and calcium-binding lysozyme, which is found in only a few species of birds and mammals. More recently, additional testes-expressed members of this family have been identified in human and mouse, suggesting that the mammalian lysozyme gene family is larger than previously known.

RESULTS

Here we characterize the extent and diversity of the lysozyme gene family in the genomes of phylogenetically diverse mammals, and show that this family contains at least eight different genes that likely duplicated prior to the diversification of extant mammals. These duplicated genes have largely been maintained, both in intron-exon structure and in genomic context, throughout mammalian evolution.

CONCLUSIONS

The mammalian lysozyme gene family is much larger than previously appreciated and consists of at least eight distinct genes scattered around the genome. Since the lysozyme c and lactalbumin proteins have acquired very different functions during evolution, it is likely that many of the other members of the lysozyme-like family will also have diverse and unexpected biological properties.

Structure and function of human α-lactalbumin made lethal to tumor cells (HAMLET)-type complexes

Human α-lactalbumin made lethal to tumor cells (HAMLET) and equine lysozyme with oleic acid (ELOA) are complexes consisting of protein and fatty acid that exhibit cytotoxic activities, drastically differing from the activity of their respective proteinaceous compounds. Since the discovery of HAMLET in the 1990s, a wealth of information has been accumulated, illuminating the structural, functional and therapeutic properties of protein complexes with oleic acid, which is summarized in this review. In vitro, both HAMLET and ELOA are produced by using ion-exchange columns preconditioned with oleic acid. However, the complex of human α-lactalbumin with oleic acid with the antitumor activity of HAMLET was found to be naturally present in the acidic fraction of human milk, where it was discovered by serendipity. Structural studies have shown that α-lactalbumin in HAMLET and lysozyme in ELOA are partially unfolded, 'molten-globule'-like, thereby rendering the complexes dynamic and in conformational exchange. HAMLET exists in the monomeric form, whereas ELOA mostly exists as oligomers and the fatty acid stoichiometry varies, with HAMLET holding an average of approximately five oleic acid molecules, whereas ELOA contains a considerably larger number (11- 48). Potent tumoricidal activity is found in both HAMLET and ELOA, and HAMLET has also shown strong potential as an antitumor drug in different in vivo animal models and clinical studies. The gain of new, beneficial function upon partial protein unfolding and fatty acid binding is a remarkable phenomenon, and may reflect a significant generic route of functional diversification of proteins via varying their conformational states and associated ligands.

The structural intolerance of the PrP alpha-fold for polar substitution of the helix-3 methionines

The conversion of the cellular prion protein (PrP(C)) into its disease-associated form (PrP(Sc)) involves a major conformational change and the accumulation of sulfoxidized methionines. Computational and synthetic approaches have shown that this change in the polarity of M206 and M213 impacts the C-terminal domain native alpha-fold allowing the flexibility required for the structural conversion. To test the effect in the full-length molecule with site-specificity, we have generated M-to-S mutations. Molecular dynamics simulations show that the replacement indeed perturbs the native state. When this mutation is placed at the conserved methionines of HaPrP(23-231), only substitutions at the Helix-3 impair the alpha-fold, stabilizing a non-native state with perturbed secondary structure, loss of native tertiary contacts, increased surface hydrophobicity, reduced thermal stability and an enhanced tendency to aggregate into protofibrillar polymers. Our work supports that M206 and M213 function as alpha-fold gatekeepers and suggests that their redox state regulate misfolding routes.

[Host defense peptides and peptidomimetics as new weapons for cancer treatment]

Host defence peptides (HDP) produced by almost all species of living organisms and widely recognized as antimicrobial antibiotics have also proved to be capable of killing a wide variety of cancer cells. In this respect they have many advantages over conventional cytotoxic chemotherapeutic agents. They seem to kill cancer cells by effects on plasma membranes and/or the membranes of mitochondria. They are often effective against multidrug-resistant cells. They have a broad spectrum of activity in that their killing effects are not restricted to particular kinds of cancer. Above all they commonly have few side effects in that they do not have the same detrimental effects on normal cells as they do on cancer cells. It has been demonstrated that HDP can be used as effective adjuvants to conventional chemotherapeutic agents. In addition they have effects on neo-angiogenesis which is important in relation to tumour growth. HDP have been shown to be powerful immunomodulators in a number of circumstances and in this respect they are believed to be instrumental in strengthening immunological host defence against cancer cells. Importantly it has also been shown that certain HDP have the capability to alter the capacity of cells to import Ca ions by affecting the location and thus function of calreticulin. Such changes it has been argued are significant in facilitating the killing of tumour cells by immunogical means. HDP constitute a novel class of anticancer agents for which, as we develop better knowledge of their pharmacokinetic profiles and learn better how to tailor their administration, hold high promise to augment or even replace the currently available cytotoxic anticancer chemotherapeutic agents most of which owe their efficacy to their capacity to bind to and damage target cell DNA.