The effect of the single substitution of arginine within the RGD tripeptide motif of a modified neurotoxin dendroaspin on its activity of platelet aggregation and cell adhesion

The Cell Adhesion Activity of the Joining Peptide of Proopiomelanocortin

Proopiomelanocortin (POMC) is a precursor protein of several peptide hormones, such as ACTH and β-endorphin. Almost all of the peptide hormones in POMC have been drastically investigated in terms of their biological activities. However, the biological activity of the joining peptide region (JP) in POMC is unknown. Therefore, to explore the biological activity of JP, sequence analyses of mammalian POMC were performed. We found an -Arg-Gly-Asp- (RGD) motif in several mammalian species, such as porcine, suggesting that JP has cell adhesion activity. To validate this hypothesis, the cell adhesion activities of the synthetic porcine JP peptides were examined using 293T cells. Cell adhesions were observed in a concentration-dependent manner of the JP peptides. In addition, the JP peptide competitively inhibited cell adhesion to the POMC-coated plates. Moreover, the cell adhesion activity of the joining peptide was inhibited by the addition of EDTA, indicating that the JP peptide mediates the cell adhesion activity via a receptor protein, integrin. Interestingly, a human JP peptide, which possesses an -Arg-Ser-Asp- (RSD) sequence in place of the RGD sequence, exhibited a higher ability in the cell adhesion activity than that of the porcine JP peptide, suggesting that the cell adhesion activity of the joining peptide is developed during the molecular evolution of POMC. In conclusion, our results reveal that the joining peptide in POMC plays an important role during cell adhesion and provide useful information related to signal transduction of nerve peptide hormones derived from POMC.

Molecular mimicry of host short linear motif-mediated interactions utilised by viruses for entry

Viruses are obligate intracellular parasites that depend on host cellular machinery for performing even basic biological functions. One of the many ways they achieve this is through molecular mimicry, wherein the virus mimics a host sequence or structure, thereby being able to hijack the host's physiological interactions for its pathogenesis. Such adaptations are specific recognitions that often confer tissue and species-specific tropisms to the virus, and enable the virus to utilise previously existing host signalling networks, which ultimately aid in further steps of viral infection, such as entry, immune evasion and spread. A common form of sequence mimicry utilises short linear motifs (SLiMs). SLiMs are short-peptide sequences that mediate transient interactions and are major elements in host protein interaction networks. This work is aimed at providing a comprehensive review of current literature of some well-characterised SLiMs that play a role in the attachment and entry of viruses into host cells, which mimic physiological receptor-ligand interactions already present in the host. Considering recent trends in emerging diseases, further research on such motifs involved in viral entry can help in the discovery of previously unknown cellular receptors utilised by viruses, as well as help in the designing of targeted therapeutics such as vaccines or inhibitors directed towards these interactions.

Isthmin-A Multifaceted Protein Family

Isthmin (ISM) is a secreted protein family with two members, namely ISM1 and ISM2, both containing a TSR1 domain followed by an AMOP domain. Its broad expression pattern suggests diverse functions in developmental and physiological processes. Over the past few years, multiple studies have focused on the functional analysis of the ISM protein family in several events, including angiogenesis, metabolism, organ homeostasis, immunity, craniofacial development, and cancer. Even though ISM was identified two decades ago, we are still short of understanding the roles of the ISM protein family in embryonic development and other pathological processes. To address the role of ISM, functional studies have begun but unresolved issues remain. To elucidate the regulatory mechanism of ISM, it is crucial to determine its interactions with other ligands and receptors that lead to the activation of downstream signalling pathways. This review provides a perspective on the gene organization and evolution of the ISM family, their links with developmental and physiological functions, and key questions for the future.

Novel disintegrin-like peptides derived from an amphibian skin cDNA sequence of Hypsiboas punctatus

Disintegrins comprise a family of small proteins that bind to and alter the physiological function of integrins, especially integrins that mediate platelet aggregation in blood. Here, we report a lysine-glycine-aspartic acid (KGD) disintegrin-like motif present in a 15-amino acid residue peptide identified in a cDNA library of the amphibian Hypsiboas punctatus skin. The original peptide sequence was used as a template from which five new analogs were designed, chemically synthesized by solid phase, and tested for disintegrin activity and tridimensional structural studies using NMR spectroscopy. The original amphibian peptide had no effect on integrin-mediated responses. Nevertheless, derived peptide analogs inhibited integrin-mediated platelet function, including platelet spreading on fibrinogen.

Snake venom three-finger toxins and their potential in drug development targeting cardiovascular diseases

Cardiovascular diseases such as coronary and peripheral artery diseases, venous thrombosis, stroke, hypertension, and heart failure are enormous burden to health and economy globally. Snake venoms have been the sources of discovery of successful therapeutics targeting cardiovascular diseases. For example, the first-in-class angiotensin-converting enzyme inhibitor captopril was designed largely based on bradykinin-potentiating peptides from Bothrops jararaca venom. In the recent years, sensitive and high throughput approaches drive discovery and cataloging of new snake venom toxins. As one of the largest class of snake venom toxin, there are now>700 sequences of three-finger toxins (3FTxs) available, many of which are yet to be studied. While the function of 3FTxs are normally associated with neurotoxicity, increasingly more 3FTxs have been characterized to have pharmacological effects on cardiovascular systems. Here we focus on this family of snake venom toxins and their potential in developing therapeutics against cardiovascular diseases.

Snake Venom Peptides: Tools of Biodiscovery

Nature endowed snakes with a lethal secretion known as venom, which has been fine-tuned over millions of years of evolution. Snakes utilize venom to subdue their prey and to survive in their natural habitat. Venom is known to be a very poisonous mixture, consisting of a variety of molecules, such as carbohydrates, nucleosides, amino acids, lipids, proteins and peptides. Proteins and peptides are the major constituents of the dry weight of snake venoms and are of main interest for scientific investigations as well as for various pharmacological applications. Snake venoms contain enzymatic and non-enzymatic proteins and peptides, which are grouped into different families based on their structure and function. Members of a single family display significant similarities in their primary, secondary and tertiary structures, but in many cases have distinct pharmacological functions and different bioactivities. The functional specificity of peptides belonging to the same family can be attributed to subtle variations in their amino acid sequences. Currently, complementary tools and techniques are utilized to isolate and characterize the peptides, and study their potential applications as molecular probes, and possible templates for drug discovery and design investigations.

Fibrinogen Motif Discriminates Platelet and Cell Capture in Peptide-Modified Gold Micropore Arrays

Human blood platelets and SK-N-AS neuroblastoma cancer-cell capture at spontaneously adsorbed monolayers of fibrinogen-binding motifs, GRGDS (generic integrin adhesion), HHLGGAKQAGDV (exclusive to platelet integrin α_IIbβ₃), or octanethiol (adhesion inhibitor) at planar gold and ordered 1.6 μm diameter spherical cap gold cavity arrays were compared. In all cases, arginine/glycine/aspartic acid (RGD) promoted capture, whereas alkanethiol monolayers inhibited adhesion. Conversely only platelets adhered to alanine/glycine/aspartic acid (AGD)-modified surfaces, indicating that the AGD motif is recognized preferentially by the platelet-specific integrin, α_IIbβ₃. Microstructuring of the surface effectively eliminated nonspecific platelet/cell adsorption and dramatically enhanced capture compared to RGD/AGD-modified planar surfaces. In all cases, adhesion was reversible. Platelets and cells underwent morphological change on capture, the extent of which depended on the topography of the underlying substrate. This work demonstrates that both the nature of the modified interface and its underlying topography influence the capture of cancer cells and platelets. These insights may be useful in developing cell-based cancer diagnostics as well as in identifying strategies for the disruption of platelet cloaks around circulating tumor cells.

Isthmin is a novel secreted angiogenesis inhibitor that inhibits tumour growth in mice

Anti-angiogenesis represents a promising therapeutic strategy for the treatment of various malignancies. Isthmin (ISM) is a gene highly expressed in the isthmus of the midbrain–hindbrain organizer in Xenopus with no known functions. It encodes a secreted 60 kD protein containing a thrombospondin type 1 repeat domain in the central region and an adhesion-associated domain in MUC4 and other proteins (AMOP) domain at the C-terminal. In this work, we demonstrate that ISM is a novel angiogenesis inhibitor. Recombinant mouse ISM inhibited endothelial cell (EC) capillary network formation on Matrigel through its C-terminal AMOP domain. It also suppressed vascular endothelial growth factor (VEGF)-basic fibroblast growth factor (bFGF) induced in vivo angiogenesis in mouse. It mitigated VEGF-stimulated EC proliferation without affecting EC migration. Furthermore, ISM induced EC apoptosis in the presence of VEGF through a caspase-dependent pathway. ISM binds to αvβ5 integrin on EC surface and supports EC adhesion. Overexpression of ISM significantly suppressed mouse B16 melanoma tumour growth through inhibition of tumour angiogenesis without affecting tumour cell proliferation. Knockdown of isthmin in zebrafish embryos using morpholino antisense oligonucleotides led to disorganized intersegmen-tal vessels in the trunk. Our results demonstrate that ISM is a novel endogenous angiogenesis inhibitor with functions likely in physiological as well as pathological angiogenesis.

Structure, function and evolution of three-finger toxins: mini proteins with multiple targets

Snake venoms are complex mixtures of pharmacologically active peptides and proteins. These protein toxins belong to a small number of superfamilies of proteins. Three-finger toxins belong to a superfamily of non-enzymatic proteins found in all families of snakes. They have a common structure of three beta-stranded loops extending from a central core containing all four conserved disulphide bonds. Despite the common scaffold, they bind to different receptors/acceptors and exhibit a wide variety of biological effects. Thus, the structure-function relationships of this group of toxins are complicated and challenging. Studies have shown that the functional sites in these 'sibling' toxins are located on various segments of the molecular surface. Targeting to a wide variety of receptors and ion channels and hence distinct functions in this group of mini proteins is achieved through a combination of accelerated rate of exchange of segments as well as point mutations in exons. In this review, we describe the structural and functional diversity, structure-function relationships and evolution of this group of snake venom toxins.

Cartilage oligomeric matrix protein promotes cell attachment via two independent mechanisms involving CD47 and alphaVbeta3 integrin

Cartilage oligomeric matrix protein (COMP) is a pentameric approximately 524 kDa multidomain extracellular matrix protein and is the fifth member of the thrombospondin family. COMP is abundantly expressed in proliferating and hypertrophic chondrocytes of the growth plate, articular cartilage, synovium, tendon, and ligament. The spatial localization of COMP highlights its importance in the phenotypes of pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED), COMP disorders that are characterized by disproportionate short stature, brachydactyly, scoliosis, early-onset osteoarthritis, and joint hypermobility. In this study, the role of COMP in ligament was investigated with a series of cell attachment assays using ligament cells binding to COMP. A dose-dependent cell attachment activity was found, which was inhibited by a peptide containing the SFYVVMWK amino acid sequence derived from the globular C-terminal domain of COMP. This activity was independent of the recently described RGD-dependent attachment activity. Function-blocking antibodies to CD47 and alphaVbeta3 integrin reduced cell attachment to COMP, implicating the participation of these cell surface molecules in COMP cell binding. Immunofluorescence studies showed that cell attachment to COMP induced the formation of lamellae containing F-actin microspikes associated with fascin. We propose that COMP promotes cell attachment via two independent mechanisms involving cell surface CD47 and alphaVbeta3 integrin and that a consequence of cell attachment to COMP is the specific induction of fascin-stabilized actin microspikes.

Protein complexes in snake venom

Snake venom contains mixture of bioactive proteins and polypeptides. Most of these proteins and polypeptides exist as monomers, but some of them form complexes in the venom. These complexes exhibit much higher levels of pharmacological activity compared to individual components and play an important role in pathophysiological effects during envenomation. They are formed through covalent and/or non-covalent interactions. The subunits of the complexes are either identical (homodimers) or dissimilar (heterodimers; in some cases subunits belong to different families of proteins). The formation of complexes, at times, eliminates the non-specific binding and enhances the binding to the target molecule. On several occasions, it also leads to recognition of new targets as protein-protein interaction in complexes exposes the critical amino acid residues buried in the monomers. Here, we describe the structure and function of various protein complexes of snake venoms and their role in snake venom toxicity.

Structure of Seneca Valley Virus-001: an oncolytic picornavirus representing a new genus

The crystal structure of Seneca Valley Virus-001 (SVV-001), the representative member of a new genus, Senecavirus, is reported at 2.3A resolution. SVV-001 is the first naturally occurring nonpathogenic picornavirus shown to mediate selective cytotoxicity towards tumor cells with neuroendocrine cancer features. The nonsegmented (+) ssRNA genome of SVV-001 shares closest sequence similarity with the genomes of the members of Cardiovirus. The overall tertiary structure of VP1-VP4 subunits is conserved with the exception of loops, especially those of VP1 that show large deviations relative to the members of the cardioviruses. The surface loops of VP1 and VP2 are predicted to mediate cell tropism of SVV-001. In addition, the organization of the packaged nucleic acid density indicates that certain regions of VP2 and VP4 interact closely with the packaged nucleic acid.