Current Protein and Peptide Science - Volume 17, Issue 4, 2016

Neurotrophins constitute a family of growth factors that play a key role in the regulation of the development and function of the central and peripheral nervous systems. A common feature of all the neurotrophins is their synthesis in cells as long precursors (pre-pro-neurotrophins) that contain an N-terminal signal peptide, a following propeptide and the mature neurotrophin. Although the signal peptide functions have been well studied, the role of neurotrophin propeptides is not so clear. Here, we briefly summarize the biochemistry of neurotrophin propeptides, including their role as foldingassistants for the mature factor and their role in processing and in secretion of neurotrophins. In the main part of the review we summarize our current state of knowledge of the biological activity of neurotrophin propeptides, their possible mechanisms of action, and their potential influence on the activity of the mature neurotrophins.

RNA modification, involving in a wide variety of cellular processes, has been identified over 100 types since 1950s. N6-methyladenosine (m6A), as one of the most abundant RNA modifications, is found in several RNA species and predominantly located in the stop codons, long internal exons as well as 3’UTR. It was reported that m6A modification preferentially appears after G in the conserved motif RRm6ACH (R = A/G and H = A/C/U). There are two families of enzymes responsible for maintaining the balance of m6A modification: m6A methyltransferases and demethylases, which add and remove methyl marks for adenosine of RNA, respectively. METTL3 complex, the m6A methyltransferases, and two kinds of demethylases including Fat mass and obesity-associated protein (FTO) and alkylation protein AlkB homolog 5 (ALKBH5) are characterized thus far. Besides the “writers” and “erasers”, m6A specific recognizing proteins, such as the YTH (YT521-B homology) domain family proteins, also have attracted significant attention. Herein, we focus on the recent progress in understanding the biological/biochemical functions and structures of proteins responsible for the m6A modification and recognition. Detailed analyses of these important proteins are essential for the further study of their biological function and will also guide us in designing more potent and specific small-molecule chemical inhibitors for these targets.

The discovery of protein chain regions responsible for protein aggregation is an important result of studying of the molecular mechanisms of prion diseases and different proteinopathies associated with the formation of pathological aggregations through the prion mechanism. The ability to control aggregation of proteins could be an important tool in the arsenal of the drug development. Here we demonstrate, on an example of RNA-binding proteins of the FET family from six animal species (human, gorilla, pig, mouse, chicken, zebra fish), the possible role of repeats within the disordered regions. For these proteins, different repeats are revealed in the prion-like (N-terminal disordered) domains, and in the C-terminal disordered regions, predicted using bioinformatics methods. Moreover, we have found that in more complex organisms the number of repeats is increased. It can be hypothesized that the presence of a large number of repeats in the disordered regions in the proteins of the FET-family could both modulate and accelerate the formation of a dynamic cross-beta structure, and pathological aggregates.

Mitogen-activated protein kinase (MAPK)-activated protein kinase (MK2) is exclusively regulated by p38 MAPK in vivo. Upon activation of p38 MAPK, MK2 binds with p38 MAPK, leading to phosphorylation of TTP, Hsp27, Akt, and Cdc25 that are involved in regulation of various essential cellular functions. In this review, we discuss current knowledge about molecular mechanisms of MK2 in regulation of TNF-α production, NADPH oxidase activation, neutrophil migration, and DNA-damage-induced cell cycle arrest which are involved in the molecular pathogenesis of acute lung injury, pulmonary fibrosis, and non-small-cell lung cancer. Collectively current and emerging new information indicate that developing MK2 inhibitors and blocking MK2-mediated signal pathways are potential therapeutic strategies for treatment of inflammatory and fibrotic lung diseases and lung cancer.

Osteogenesis involves a cascade of processes wherein mesenchymal stem cells differentiate towards osteoblasts, strictly controlled by a number of regulatory factors. Runx2 protein is a key transcription factor which serves as a master regulator for osteogenesis by activating the promoters of various osteoblastic genes. Runx2 is regulated by several cofactors, including the histone deacetylase enzymes known as HDACs. HDACs are a family of proteins that regulate gene expression and/or activity through the mechanism of deacetylation and they can be divided into four classes, namely classes I, II, III and IV HDACs based on their sequence identity and nuclear or cytoplasmic localization. Knockout studies of all classes of HDACs showed their specific developmental roles. Evidence has proved Runx2 to be a repressible target of HDACs and this interplay is found to be a crucial factor controlling osteoblast differentiation. Further, another level of osteogenic regulation involves microRNAs (miRNAs), which are small, non-coding endogenous molecules capable of gene silencing by partial or complete complementary binding of their seed sequences to the 3’ untranslated region (UTR) of target mRNAs. In this study, the recent developments on identifying the function of HDACs on Runx2 expression/activity and the impact of miRNAs on HDACs in regulation of osteogenesis are reviewed.

This is a first part of the two-part article that continues a series of reviews on the abundance and roles of intrinsic disorder in milk proteins. We introduce here α-lactalbumin, a small (Mr 14 200), simple, acidic (pI 4–5), Ca2+-binding protein that might constitute up to 20% of total milk protein. Although function (it is one of the two components of lactose synthase that catalyzes the final step of the lactose biosynthesis in the lactating mammary gland), structure (protein has two domains, a large α -helical domain and a small β -sheet domain connected by a calcium binding loop), and folding mechanisms (α-lactalbumin is well-known as a classic example of the molten globule state) of this model globular protein are relatively well understood, α-lactalbumin continues to surprise researchers and clearly continues to have high discovery potential. The goal of this review is to summarize some recent advances in the field of α-lactalbumin research and to analyze the peculiarities of the “intrinsic disorder code” of this protein.

This article is a continuation of a series of reviews on the presence and the role of intrinsic disorder in milk proteins in the journal of Current Protein and Peptide Science. The focus of this article is on casein phosphopeptides, which are liberated during digestion of the milk protein casein. Structurally these phosphopeptides have multiphosphorylated regions making them highly charged. The high degree of charge coupled with relatively low instances of hydrophobic amino acids makes them intrinsically disordered. These peptides have anticariogenic, antimicrobial, immunomodulatory, and cytomodulatory properties. Recent work using in vivo and in vitro models suggests that in addition to transporting calcium, these peptides can also enhance its bioaccessibility. The mechanism of this enhancement has yet to be determined. We review the current state of their structure, function, and isolation of these peptides.

In 2004, Neuropeptide S (NPS) was identified to be the cognate ligand of the previously discovered orphan receptor GPCR 154, now termed as NPS receptor (NPSR). Since, then a wealth of data has elucidated the unique behavioral profile of this peptidergic system in numerous physiological function such as being pro-arousal and anxiolytic at the same time. Besides, its robust anxiolytic profile, this peptide system has been found to activate HPA axis and concomitant release of ACTH and corticosterone. Additionally, the involvement of NPS in reinstatement of drug seeking behavior has also been reported. In recent years, accumulating data from various labs have demonstrated an A/T single-nucleotide polymorphism (SNP) resulting in (Asn107Ile) switch in the human NPSR gene as the risk factor for various psychiatric disorders such as panic disorder, post traumatic syndrome, alcohol use disorders and enhanced anxiety sensitivity, although, this is in stark contrast to the findings made in animal models which have consistently projected the anxiolytic nature of this peptide system. Therefore, in context of robust involvement of NPS system in various psychiatric disorders this review article considers the importance of NPS from translational point of view and appraises the need of therapies to be tailored around NPSR. In this respect, pharmacology of important NPSR ligands which have been recently developed has been discussed together with their possible side effects profile. Additionally, this review article encompasses all recent developments in the field of NPS system highlighting the role of this neuropeptide in all those biological functions which are modulated by this system. The role of this peptide has been discussed in detail in the perspective of sleep regulation, anxiety, fear expression and most importantly in drug addiction. Additionally, neuroimaging and genetic linkage studies addressing the functional impact of NPSR1 variants in the aforementioned psychiatric disorders have also been discussed.