Current Protein and Peptide Science - Volume 17, Issue 8, 2016

As a family of chromatin remodeling proteins, metastasis-associated proteins (MTAs) have shown to be the master regulators in both physiological and pathological contexts. Although MTA3 is the latest being identified in MTA family, it has started to draw as much attention as the other family members. MTA3 is expressed in various tissues and is associated with different physiological functions. In cancerous context, both MTA1 and MTA2 are generally considered as oncogenes because they are capable of enhancing metastasis. However, MTA3 appears to play more complicated roles in cancers depending on the contexts. As a tumor suppressor, MTA3 usually down-regulates Snail, the master regulator of epithelium-mesenchymal transition, and subsequently represses cancer cell invasion and migration. Additionally, MTA3 may function by enhancing cancer cell differentiation without affecting proliferation in certain cancers. On the other hand, MTA3 might function in oncogene - related properties similarly as MTA1 and MTA2. In this review, we summarize our current understanding about MTA3 in normal development, cancers as well as other human diseases by comparing the similarities and differences between MTA3 and the other members of the MTA family.

This is a concluding part of the three-part article from a series of reviews on the abundance and roles of intrinsic disorder in milk proteins. In this paper, we describe the peculiarities of metal binding to a multifunctional milk protein, α-lactalbumin, which has two domains, a large α-helical domain and a small β-sheet domain connected by a calcium binding loop. It is known that in addition to four disulfide bonds, the native fold of this protein is stabilized by binding of a calcium ion. In fact, although in various mammals, α-lactalbumins are rather poorly conserved possessing the overall sequence identity of ~16%, the positions of all eight cysteines and a calcium binding site (residues DKFLDDDITDDI in human protein) are strongly conserved. Curiously, this conserved calcium binding loop is located within a region with increased structural flexibility. Besides canonical calcium binding, α-lactalbumin is known to interact with other metals, such as zinc (for which it has a specific binding site), and, in its apo-form, it can bind other divalent and monovalent cations. The binding of Mg2+, Na+, and K+ to the Ca2+ site increases α-lactalbumin stability against action of heat and various denaturing agents, with the higher stabilization effects being imposed by the stronger bound metal ions.

Among three major replicative DNA polymerases of the B-family, Pol α, Pol δ and Pol , Pol δ plays an essential role in chromosomal DNA replication and is also involved in various DNA repair processes in eukaryotes. Human Pol δ is commonly viewed as a heterotetrameric complex, consisting of the catalytic subunit p125 and second subunit p50, together with two additional accessory subunits, p68 and p12. A growing body of research has shown that the latter subunits play a critical role in the regulation of Pol δ functions. The formation of a new form of Pol δ, heterotrimer Pol δ3, is found by virtue of the depletion of p12 through the ubiquitin–proteasome pathway in response to DNA damages that are trigged by UV irradiation, alkylating agents, oxidative and replication stresses. Pol δ3 exhibits significant differences in properties to its progenitor with a major impact on cellular processes in genomic surveillance, DNA replication and DNA repair. Our recent studies indicate that there exists an alternative pathway for Pol δ3 formation by calpain-mediated proteolysis of p12 in a calcium-triggered apoptosis in living cells. In this article, we review and discuss the recent advances from our group and others in the studies of human Pol δ with an emphasis on the generation of its multiple forms by reconstitution and subsequent alternations in enzymatic properties, the multiple pathways of the Pol δ3 formation in living cells, and the phylogenetic analysis of the evolutionary history on POLD4 gene that is for the p12 subunit.

Biosimilars are biotechnologically manufactured products that enter the market as and when the original biopharmaceutical goes off patent. As the name suggests, they are only “similar” and not exact versions of the originator product. The manufacturing process of biosimilars is complex, the product prone to variation, and regulatory approval rules are more extensive and elaborative than required for generic versions of chemically synthesized drugs. This makes the field of biosimilars interesting and inquisitive for research. As biosimilars are essentially protein drugs manufactured in living cells, immunogenicity becomes a major issue in almost all biopharmaceuticals. This increases the importance of Risk Management Plan (RMP) and pharmacovigilance. Since biosimilars are not identical copies of innovator products, the regulatory facets of indication extrapolation, automatic substitution, and interchangeability are more stringent than those available for small molecule generic drugs. This article discusses all these sectors significant to the world of biosimilars. Prospectively, biosimilars have the potential to deliver effective cost savings for healthcare users and thus they are a critical part of the biopharmaceutical industry.

The High mobility group box 1 (HMGB1) protein is an extremely versatile, highly conserved nuclear protein, with its unique intracellular and extracellular functions mediated by its relatively simple domain structure. Within the nucleus, HMGB1 binds to DNA minor groove in a nonspecific manner and causes bends in the double helix thus helps in recruiting a number of DNA binding protein and transcription factors, to facilitate transcription of various genes. HMGB1 also helps in DNA repair, chromatin remodeling, V (D) J recombination, and assembly of nucleosome on the chromatin. On contrary, under pathological conditions HMGB1 displays inflammatory response by interaction with specific cell surface receptors like RAGE, TLR-4, TLR9, and TLR2 and activates NF-kB downstream signaling pathways. The upregulation of HMGB1 is directly associated with the pathogenesis of cancer, sepsis, ischemia, hemorrhagic shock, anorexia, rheumatic disease, periodontal disease etc. Therefore, HMGB1 has been considered as a promising target in the treatment of various human diseases. The interest in HMGB1 is evident and reflected in the exponential increase in the recent publications, and therefore there is a need for an update on the understanding of the role of HMGB1 in pathogenesis and its potential application of HMGB1 as a therapeutic target in a number of human diseases.

Antibody-mediated rejection (AMR) is relatively uncommon in AB0-compatible liver grafts; however, recent data suggest that antibody-mediated mechanisms may play a role in the differential pathogenesis of liver graft rejection. In this sense, it has been shown that staining for diffuse C4d deposition (in endothelium or stroma of portal tracts or sinusoids) could be used as a tissue biomarker of humoral allograft rejection and fibrosis in biopsies obtained in post-transplantation period, in addition to the determination of donor specific antibodies (DSA). Therefore, more stringer criteria have to be established in order to define real antibody-mediated injury (acute rejection, chronic rejection or fibrosis development) in liver graft transplant. These criteria should intend to correlate allograft dysfunction associated with compatible histological findings, presence of DSAs and C4d positivity and should be clarified with respect to rejection injury frequency, its severity and its response to antibody-depleting immunosuppression in the future. This could improve our progressive understanding of the clinical-pathological characteristic and diagnostic approaches of AMR and fibrosis.

Antibiotics are one of the most important discoveries in the 20th century and have been widely used for treating animal diseases in the 21st century. However, antibiotic resistance among bacterial pathogens and widespread concerns regarding their use in animals has received great attention all over the world. Great attention has focused on scientific breakthroughs of the alternatives to antibiotics. Various materials such as enzymes, prebiotics, probiotics, minerals, antimicrobial peptides, acidifiers, plants and plant extracts have been tested as possible antibiotics alternatives. Owing to their effects on intestinal microbiota and immune function, research efforts have been conducted on the application of these feed supplements. This review highlights promising research results about the alternatives to antibiotics in animal husbandry that are expected to beneficially limit the adverse effects of antibiotics and ensure the safety of animal-derived foods and the environment.

Lectins are proteins/glycoproteins of non-immune origin, which are widely distributed in nature. They have at least one non-catalytic domain, which binds reversibly to specific monosaccharides or oligosaccharides. Lectins recognizing sugar moieties in cell walls or cell membranes alter the membrane physiology and trigger biochemical changes in the cell. Thus, various applications of lectins have been described, for example as tools to identify aberrant glycans expressed by neoplastic cells and as antitumor agents by inducing apoptosis by various mechanisms. In order to widen applications of anti-tumor lectins, a detailed investigation of their action mechanism is required. Mushrooms are a valuable source of novel lectins with unique specificities and potentials for biotechnological and biomedical applications. This article reviews information on anti-proliferative activity of mushroom lectins obtained in-vitro and in-vivo. The possible role of lectins as cancer therapeutics is discussed together with the mechanisms underlying the anti-proliferative activity, which may help to exploit these biomolecules as potential novel antitumor drugs in near future.

Exosomes are small vesicles that are released from a variety of cells and are involved in cell-to-cell communication. In humans, exosomes are detected in the plasma, urine, saliva, and cerebrospinal fluid. These vesicles carry multiple cargo proteins, as well as microRNA that affect the transcription of target genes. During cancer progression, secretion of exosomes increases. As such, proteins and microRNAs released from exosomes in cancer patients can be used as biomarkers for cancer diagnosis and progression. Yeast is an excellent model system to study trafficking of small vesicles in and out of the cells. When yeast cells are grown in low glucose, small vesicles transport gluconeogenic enzymes to different locations. In the cytoplasm, they exist as free vesicles and aggregated clusters. They are also secreted and account for more than 90% of total organelles in the extracellular fraction. When glucose is added to prolongedstarved cells, extracellular vesicles are endocytosed resulting in a dramatic decrease in vesicles in the extracellular fraction and the appearance of vesicle clusters in the cytoplasm. Internalization also leads to a rapid decline in protein levels for vesicle-associated proteins in the extracellular fraction. Using large-scale proteomics/secretomics, more than 300 proteins that were secreted into the extracellular fraction/periplasm were identified. They showed distribution patterns similar to gluconeogenic enzymes. They were secreted during glucose starvation and their levels in the extracellular fraction decreased following glucose re-feeding. Multiple techniques have been used to study the biogenesis, clustering, secretion, and internalization of vesicles in yeast.

The identification of Klotho gene was a major discovery as the gene encodes a protein regulating multiple functions. A defect in Klotho gene expression in mice results in a phenotype of premature aging including shortened life span, growth retardation, hypogonadism, skin and muscle atrophies, vascular calcification, cognition impairment, motor neuron degeneration and others. This phenotype is associated with phosphate balance disorders and underlines the major function of Klotho in mineral metabolism. As another 2 related paralogs were discovered (beta-Klotho, which is involved in bile acid and energy metabolism, and gamma-Klotho, with a yet to be defined function), this led to the revised naming of Klotho as alpha-Klotho. Two forms of alpha-Klotho protein have been reported: a membrane-bound and a soluble one. Membrane Klotho forms a complex with fibroblast growth factor (FGF) receptors and functions as an obligate co-receptor for the FGF-23 phosphatonin in distal tubules. The soluble form of Klotho seems to function as a humoral factor and regulates glycoproteins on the cell surface including ion channels and growth factors. There is data suggesting that soluble Klotho exerts phosphaturic effects independently of FGF-23. Circulating soluble Klotho is produced either by proteolytic cleavage of the extracellular domain of the transmembrane form by two membrane-anchored proteases (ADAM10 and ADAM17) or by alternative mRNA splicing. In animal models Klotho has been shown to exert pleiotropic actions, including cytoprotection, anti-oxidation, anti-apoptosis, protection of vasculature, promotion of angiogenesis and vascularization, inhibition of fibrogenesis and preservation of stem cells. The exact diagnostic and therapeutic role of Klotho in humans is not fully known yet. The article presents the role of Klotho in physiology and different stages of chronic kidney disease (CKD).

Membrane interacting peptides of natural or synthetic origins serve a variety of biological purposes. They have been extensively studied for their involvement in immunity, diseases, and for their potential as medical therapeutics and research tools. In this review membrane interacting peptides are categorized into four groups according to their function: antimicrobial peptides, cell-penetrating peptides, channel forming peptides and amyloid peptides. A historical overview of the development, their functional mechanisms, and recent advances are presented for each of the groups. Considerable research is still devoted to this field of study and in this report a representative sample of the latest studies is presented. A set of common features among peptide groups emerges as the understanding of their action mechanisms increase. The possibility of a membrane centric general model for peptide-membrane interaction is also discussed. This review seeks to provide a unifying view of the field and promote the interaction between research groups working on peptides that have so far been studied as belonging to completely different fields.