Current Chemical Biology - Volume 4, Issue 2, 2010

Understanding the mechanisms by which amyloid fibrils are formed, both in vivo and in vitro, is vital for developing methods to treat and prevent debilitating deposition diseases such as Alzheimer's disease, Parkinsona's disease, type II diabetes and systemic amyloidoses. In recent years, computer modelling and biophysical studies have broadened our understanding of the biochemical mechanisms underpinning protein aggregation. As a result, it is now believed that the ability to form fibrils is an intrinsic property of polypeptide chains and not isolated to disease-related proteins or peptides. Molecular chaperones are a diverse group of functionally related proteins well known for their ability to suppress amyloid formation, and are likely to be important determinants in deciding the fate of protein aggregation prone proteins in vivo. Evidence is presented that suggests that there is striking commonality in the anti-amyloidogenic activity of molecular chaperones regardless of their structural and spatial differences. In this review, we focus on what in vitro biophysical studies tell us about amyloid formation and molecular chaperones, and how investigating the role of chaperones in fibril formation can enhance our understanding of protein misfolding diseases.

Many plants produce enzymes with N-glycosidase activity, also known as Ribosome Inactivating Proteins. These proteins remove a specific adenine residue from the ribosomal RNA (28S in eukaryotes) inducing the block of protein synthesis by inhibiting the binding of the Elongation Factor 2. Both eukaryotic and prokaryotic ribosomes (with different sensitivity) can irreversibly be damaged by the action of these enzymes, suggesting their use as cytotoxic drugs. In fact several applications of targeted N-glycosidases have been developed (i.e. immunotoxins) for the treatment of human diseases such as leukaemia, but biotechnological development has furthermore suggested new applications of targeted N-glycosidases (i.e. Ig192-saporin) that are now used as powerful tools for cell biology research. The high number of enzymes available and the possibility to express these proteins as recombinant products, allow to predict new formulations and applications discussed in this paper starting from the example of the model toxins ricin and saporin.

Carnitine homeostasis has a pivotal role in the life of mammals. It is realized by the carnitine system, which consists of networks of enzymes and membrane transporters and plays an essential role in functions such as the regulation of the CoA/acyl-CoA ratio, the supply of substrates for the β-oxidation to mitochondria and peroxisomes and of acyl units for VLDL assembly to the ER, the efflux of acetyl groups from mitochondria during glucose metabolism and the detoxification of the organism. The network of the transporters plays a crucial role in maintaining homeostasis since it allows the absorption, excretion and re-absorption of carnitine and carnitine derivatives as well as the flux of these metabolites through different tissues and within sub-cellular compartments. Several transport systems which were thought to be involved in the network have been identified and characterized to a certain extent. These are the plasma membrane transporters OCTN1, 2 and 3, the mitochondrial CACT and the carnitine transport system of endoplasmic reticulum (ERCT). These transporters have been functionally characterized by studies in eukaryotic cell systems and/or in reconstituted liposomes. Interestingly, it was found that some commonly used drugs interact with different carnitine transporters, causing alterations of the transport function by displacing the substrate from the binding site or by irreversibly inactivating the transporters. These interactions will cause derangements of the carnitine homeostasis. The current knowledge of the characterization of the carnitine transporter network and the interaction with drugs are reviewed with emphasis to the most recent data obtained using the proteoliposome reconstituted systems.

Anisomycin is a bacterial antibiotic isolated from Streptomyces griseolus. Anisomycin is mainly known as a potent and reversible inhibitor of protein synthesis in eukaryotic organisms that acts by binding and inhibiting peptidyl transferase activity of 60S ribosomal subunit. Interestingly, anisomycin has been widely used as an extremely potent activator of mitogen-activated protein kinase (MAPK) cascades in mammalian cells, especially of JNK, p38, and ERK1/2, and it can also modulate other signal transduction pathways. Regulation of gene expression is another intriguing effect of anisomycin given that it is able to superinduce the expression of certain genes, or cause degradation of some proteins. Furthermore, it also affects both pro- and anti-apoptotic mechanisms. Recently, a potential therapeutic use for anisomycin has been proposed as it can sensitize malignant cells to death, either alone or in combination with certain drugs; anisomycin may also function as an immunosuppressant by inhibiting T cells and transplant rejection in mice. Anisomycin has been applied in the study of memory in animals, and it has been shown that it inhibits the consolidation of new memories and cause amnesia; however, it is necessary to carry out more studies in order for anisomycin to be considered as a potential psychiatric drug in humans. Notably, the multifunctional feature of anisomycin has yielded great benefits for biochemical research even though some of its mechanisms of action remain unknown.

Vessel calcification involves an active cellular process. However, the events by which calcification occurs in vascular endothelial cells have not been sufficiently studied. We performed experiments that evaluated the effect of osteogenic medium (OM) on alkaline phosphatase activity, signaling pathways and cell death in human umbilical vein endothelial cells (HUVEC). We found that OM emits a survival signal at the beginning of cell culture and then causes massive cell death. The formation of intracellular calcium accumulation led to complete calcification spread by alkaline phosphatase produced in stimulated cells. To better understand the signaling networks involved, we analyzed the HUVEC- and HUVEC-treated cell lysates using the Kinexus™ KPSS 1.3 phospho-site pathway screen. Our studies revealed that STAT3 Serine 727 phosphorylation is enhanced in HUVEC. Treatment with 5-aza-2'-deoxycytidine led up to inhibition of calcium accumulation induced by OM. These data suggest that under calcifying conditions, STAT3 is a potential important mediator of calcium uptake in endothelial cells. Continuing research is revealing the similarities, differences and deficiencies of STAT3 activities in diverse processes including the calcification of vessels.

An efficient route for the synthesis of 6-(1-benzofuran-2-yl)-2-phenyl imidazo[2,1-b] [1,3,4] thiadiazole(4a-e), was achieved by the reaction of 1-(1-benzofuran-2-yl)-2-bromoethanone (2) with 5-aryl-1,3,4-thiadiazol-2-amine(3-ae). The reaction mixture containing compound 4d with secondary amines and formaldehyde with catalytic amount of acetic acid, furnished corresponding Mannich bases (5-7). All newly synthesized compounds were screened for analgesic and antimicrobial activity. Among all the compounds tested for antibacterial activity, compound 7 showed significant activity against S. aureus when compared to other compounds, compound 4a, 4d and 5 exhibited highest activity against B. subtilis, compound 4b, 4d and 7 exhibited equipotent activity against K. pneumoniae and compound 6 exhibited promising activity against E. coli comparable with the standard drug Tetracycline. Among all the compounds tested for antifungal activity, the compound 4b and 4c exhibited significant activity against A. niger, compound 4c and 4e showed highest activity against C. albicans, compound 7 exhibited promising activity against P. chrysozenous and compound 4a and 4b exhibited highest activity against T. vridar as compared with standard drug Flucanozole. Compound 4b and 4d proved to be potent analgesic agents, as they exhibited significant analgesic activity comparable to standard drug and the remaining compounds showed moderate activity as compared to standard drug.

Nanomaterials have one dimension < 100nm and possess chemical properties dictated by chemical composition, their unusually small size and very large proportional surface area. Even chemically inert materials can have significant chemical activity on the nanoscale (e.g. surface catalysis). Some nanomaterials are toxic in biological scenarios but remarkably little is known about this, especially in terms of key attributes underlying toxicity. Recent research suggests that nanomaterials can cross important biobarriers (e.g. blood-brain), enter cells and trigger oxidative stress by production of reactive oxygen species. Key factors in nanomaterial toxicity seem to be size, structure, chemical composition and a “corona” of proteins coating the particle which may confer biological functionality. Nanomaterials have extensive applications in low-volume, high-value scenarios such as biomedical devices but it is projected that they will increasingly feature in high-volume, low value applications (e.g. food packagings). Thus, nanomaterials may present an emerging longterm environmental threat. This review summarizes some of the key recent studies on nanomaterial toxicity in a variety of biological systems; the biological consequences of this toxicity and attributes of nanoparticles implicated in toxicity. The wider environmental implication of large-scale nanomaterial use is also discussed and perspectives for future research explored.

The heavy metal cadmium (Cd) is an environmental toxin that causes specific problems in liver, kidney, bone and reproductive tissue. It is thought to act as both carcinogen and co-carcinogen, and it causes developmental anomalies in a number of animal species. Numerous mechanisms are thought to underlie these toxic and teratogenic effects, including genotoxicity, oxidative stress and caspase activation. One of the most remarkable observed histological effects of Cd, however, is breakdown of intercellular junctions, with consequent alteration of cell morphology and apoptosis. Therefore, in this review, the effects of Cd on cellular adhesion are examined, and possible effects on embryological development and clinical disease are discussed.

Improper allocation of the incorrect metal ion to a metalloprotein can have resounding and often detrimental effects on different aspects of cellular physiology. Enzymes that employ transition metals as co-factors are housed in a wide variety of intracellular locations or are exported to the extracellular milieu. Metallochaperones (much smaller than the cell) are essential for the proper functioning of cells and are a distinct class of proteins which accounts for the incorporation of metal ion cofactors into metalloenzymes / metalloproteins. Metals in the cells are distributed by metallochaperones (intracellular metal ion carriers) and these intracellular metal ion carriers ensure that the correct metal is acquired by a specific metalloenzyme. Metallochaperones act in the intracellular trafficking of metal ions to protect the cell and are a family of soluble metal receptor proteins that bind and protect metal ions/cofactors. The target sites for metal/cofactor delivery include a number of metalloenzymes, or proteins that bind metal ions and use these ions as cofactors to perform essential biochemical reactions such as cellular respiration, DNA synthesis and antioxidant defense. In this review, metallochaperones for various metals such as copper, nickel, zinc, iron, arsenic, manganese, cobalt, molybdenum and vanadium are discussed. In the cell, the specific metal ion is often selected by specific protein-protein interactions between the apoprotein and a metallochaperone and ligand-exchange reactions have been involved in the metal transfer from metallochaperones to cognate apoproteins. The development of chaperone-based medications from medicinal plants has been reported.